Related
I have an issue with handling JSON data from an api that I use in my application. The problem is that the JSON contains some properties that are an object when there is an item, and become an array when there are more items. So that's a structure like this:
[
{
"MyObj": {
"Foo": "Bar"
}
},
{
"MyObj": [
{
"Foo": "Bar1"
},
{
"Foo": "Bar2"
}
]
}
]
I've tried several JSON to C# converters, some of them generate a property of type object, the quicktype.io converter generates this:
public class Example
{
[JsonProperty("MyObj")]
public MyObjUnion MyObj { get; set; }
}
public partial class MyObjElement
{
[JsonProperty("Foo")]
public string Foo { get; set; }
}
public struct MyObjUnion
{
public MyObjElement MyObjElement;
public MyObjElement[] MyObjElementArray;
public static implicit operator MyObjUnion(MyObjElement MyObjElement) => new MyObjUnion { MyObjElement = MyObjElement };
public static implicit operator MyObjUnion(MyObjElement[] MyObjElementArray) => new MyObjUnion { MyObjElementArray = MyObjElementArray };
}
internal class MyObjUnionConverter : JsonConverter
{
public override bool CanConvert(Type t) => t == typeof(MyObjUnion) || t == typeof(MyObjUnion?);
public override object ReadJson(JsonReader reader, Type t, object existingValue, JsonSerializer serializer)
{
switch (reader.TokenType)
{
case JsonToken.StartObject:
var objectValue = serializer.Deserialize<MyObjElement>(reader);
return new MyObjUnion { MyObjElement = objectValue };
case JsonToken.StartArray:
var arrayValue = serializer.Deserialize<MyObjElement[]>(reader);
return new MyObjUnion { MyObjElementArray = arrayValue };
}
throw new Exception("Cannot unmarshal type MyObjUnion");
}
public override void WriteJson(JsonWriter writer, object untypedValue, JsonSerializer serializer)
{
var value = (MyObjUnion)untypedValue;
if (value.MyObjElementArray != null)
{
serializer.Serialize(writer, value.MyObjElementArray);
return;
}
if (value.MyObjElement != null)
{
serializer.Serialize(writer, value.MyObjElement);
return;
}
throw new Exception("Cannot marshal type MyObjUnion");
}
public static readonly MyObjUnionConverter Singleton = new MyObjUnionConverter();
}
Although this does work correctly, it's still a bit cumbersome because to get the data you always need to check if it's in the MyObjElement or MyObjElementArray class.
So the question is if there are other, more elegant ways to solve this issue. (Other than changing the API output, which is not mine)
If you know the data structure before hand, I would create a custom data model for the Json file and then deserialise it like so:
CurrencyExchangeRates deserialisedData = JsonConvert.DeserializeObject<CurrencyExchangeRates>(savedData);
foreach (CurrentRate value in deserialisedData.ExchangeRates)
{
rate.ExchangeRates.Add(new CurrentRate { Rate = value.Rate, Timestamp = value.Timestamp });
}
This is how I did that in an application. Hope this helps a little.
You can check and cast each object in your JSON depending the type of object.
For example consider using Newtonsoft.Json library for JSON parsing, you can do the following:
// considering your JSON string
string jsonString = "[{'MyObj':{'Foo':'Bar'}},{'MyObj':[{'Foo':'Bar1'},{'Foo':'Bar2'}]}]";
// parse your JSON into JTokens
var tokens = JToken.Parse(jsonString);
// iterate through all the tokens
foreach (var token in tokens)
{
// your token is a grand child
JToken myObj = token.First.First;
// check if the grand child is array
if (myObj is JArray)
{
// cast the grand child token into MyObj list or array object
IEnumerable<MyObj> objList = myObj.ToObject<List<MyObj>>();
Console.WriteLine("converted to MyObj Array");
}
else if (myObj is JObject) // else if its a non array item
{
// cast the grand child token into MyObj object
MyObj obj = myObj.ToObject<MyObj>();
Console.WriteLine("converted to MyObj");
}
}
// your MyObj Type will look like this:
public class MyObj
{
public string Foo { get; set; }
}
I'm trying to fix my SendGridPlus library to deal with SendGrid events, but I'm having some trouble with the inconsistent treatment of categories in the API.
In the following example payload taken from the SendGrid API reference, you'll notice that the category property for each item can either be a single string or an array of strings.
[
{
"email": "john.doe#sendgrid.com",
"timestamp": 1337966815,
"category": [
"newuser",
"transactional"
],
"event": "open"
},
{
"email": "jane.doe#sendgrid.com",
"timestamp": 1337966815,
"category": "olduser",
"event": "open"
}
]
It seems my options to make JSON.NET like this are fixing the string before it comes in, or configuring JSON.NET to accept the incorrect data. I'd rather not do any string parsing if I can get away with it.
Is there any other way I can handle this using Json.Net?
The best way to handle this situation is to use a custom JsonConverter.
Before we get to the converter, we'll need to define a class to deserialize the data into. For the Categories property that can vary between a single item and an array, define it as a List<string> and mark it with a [JsonConverter] attribute so that JSON.Net will know to use the custom converter for that property. I would also recommend using [JsonProperty] attributes so that the member properties can be given meaningful names independent of what is defined in the JSON.
class Item
{
[JsonProperty("email")]
public string Email { get; set; }
[JsonProperty("timestamp")]
public int Timestamp { get; set; }
[JsonProperty("event")]
public string Event { get; set; }
[JsonProperty("category")]
[JsonConverter(typeof(SingleOrArrayConverter<string>))]
public List<string> Categories { get; set; }
}
Here is how I would implement the converter. Notice I've made the converter generic so that it can be used with strings or other types of objects as needed.
class SingleOrArrayConverter<T> : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(List<T>));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JToken token = JToken.Load(reader);
if (token.Type == JTokenType.Array)
{
return token.ToObject<List<T>>();
}
return new List<T> { token.ToObject<T>() };
}
public override bool CanWrite
{
get { return false; }
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
Here is an short program demonstrating the converter in action with your sample data:
class Program
{
static void Main(string[] args)
{
string json = #"
[
{
""email"": ""john.doe#sendgrid.com"",
""timestamp"": 1337966815,
""category"": [
""newuser"",
""transactional""
],
""event"": ""open""
},
{
""email"": ""jane.doe#sendgrid.com"",
""timestamp"": 1337966815,
""category"": ""olduser"",
""event"": ""open""
}
]";
List<Item> list = JsonConvert.DeserializeObject<List<Item>>(json);
foreach (Item obj in list)
{
Console.WriteLine("email: " + obj.Email);
Console.WriteLine("timestamp: " + obj.Timestamp);
Console.WriteLine("event: " + obj.Event);
Console.WriteLine("categories: " + string.Join(", ", obj.Categories));
Console.WriteLine();
}
}
}
And finally, here is the output of the above:
email: john.doe#sendgrid.com
timestamp: 1337966815
event: open
categories: newuser, transactional
email: jane.doe#sendgrid.com
timestamp: 1337966815
event: open
categories: olduser
Fiddle: https://dotnetfiddle.net/lERrmu
EDIT
If you need to go the other way, i.e. serialize, while keeping the same format, you can implement the WriteJson() method of the converter as shown below. (Be sure to remove the CanWrite override or change it to return true, or else WriteJson() will never be called.)
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
List<T> list = (List<T>)value;
if (list.Count == 1)
{
value = list[0];
}
serializer.Serialize(writer, value);
}
Fiddle: https://dotnetfiddle.net/XG3eRy
I was working on this for ages, and thanks to Brian for his answer.
All I am adding is the vb.net answer!:
Public Class SingleValueArrayConverter(Of T)
sometimes-array-and-sometimes-object
Inherits JsonConverter
Public Overrides Sub WriteJson(writer As JsonWriter, value As Object, serializer As JsonSerializer)
Throw New NotImplementedException()
End Sub
Public Overrides Function ReadJson(reader As JsonReader, objectType As Type, existingValue As Object, serializer As JsonSerializer) As Object
Dim retVal As Object = New [Object]()
If reader.TokenType = JsonToken.StartObject Then
Dim instance As T = DirectCast(serializer.Deserialize(reader, GetType(T)), T)
retVal = New List(Of T)() From { _
instance _
}
ElseIf reader.TokenType = JsonToken.StartArray Then
retVal = serializer.Deserialize(reader, objectType)
End If
Return retVal
End Function
Public Overrides Function CanConvert(objectType As Type) As Boolean
Return False
End Function
End Class
then in your class:
<JsonProperty(PropertyName:="JsonName)> _
<JsonConverter(GetType(SingleValueArrayConverter(Of YourObject)))> _
Public Property YourLocalName As List(Of YourObject)
Hope this saves you some time
As a minor variation to the great answer by Brian Rogers, here are two tweaked versions of SingleOrArrayConverter<T>.
Firstly, here is a version that works for all List<T> for every type T that is not itself a collection:
public class SingleOrArrayListConverter : JsonConverter
{
// Adapted from this answer https://stackoverflow.com/a/18997172
// to https://stackoverflow.com/questions/18994685/how-to-handle-both-a-single-item-and-an-array-for-the-same-property-using-json-n
// by Brian Rogers https://stackoverflow.com/users/10263/brian-rogers
readonly bool canWrite;
readonly IContractResolver resolver;
public SingleOrArrayListConverter() : this(false) { }
public SingleOrArrayListConverter(bool canWrite) : this(canWrite, null) { }
public SingleOrArrayListConverter(bool canWrite, IContractResolver resolver)
{
this.canWrite = canWrite;
// Use the global default resolver if none is passed in.
this.resolver = resolver ?? new JsonSerializer().ContractResolver;
}
static bool CanConvert(Type objectType, IContractResolver resolver)
{
Type itemType;
JsonArrayContract contract;
return CanConvert(objectType, resolver, out itemType, out contract);
}
static bool CanConvert(Type objectType, IContractResolver resolver, out Type itemType, out JsonArrayContract contract)
{
if ((itemType = objectType.GetListItemType()) == null)
{
itemType = null;
contract = null;
return false;
}
// Ensure that [JsonObject] is not applied to the type.
if ((contract = resolver.ResolveContract(objectType) as JsonArrayContract) == null)
return false;
var itemContract = resolver.ResolveContract(itemType);
// Not implemented for jagged arrays.
if (itemContract is JsonArrayContract)
return false;
return true;
}
public override bool CanConvert(Type objectType) { return CanConvert(objectType, resolver); }
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
Type itemType;
JsonArrayContract contract;
if (!CanConvert(objectType, serializer.ContractResolver, out itemType, out contract))
throw new JsonSerializationException(string.Format("Invalid type for {0}: {1}", GetType(), objectType));
if (reader.MoveToContent().TokenType == JsonToken.Null)
return null;
var list = (IList)(existingValue ?? contract.DefaultCreator());
if (reader.TokenType == JsonToken.StartArray)
serializer.Populate(reader, list);
else
// Here we take advantage of the fact that List<T> implements IList to avoid having to use reflection to call the generic Add<T> method.
list.Add(serializer.Deserialize(reader, itemType));
return list;
}
public override bool CanWrite { get { return canWrite; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var list = value as ICollection;
if (list == null)
throw new JsonSerializationException(string.Format("Invalid type for {0}: {1}", GetType(), value.GetType()));
// Here we take advantage of the fact that List<T> implements IList to avoid having to use reflection to call the generic Count method.
if (list.Count == 1)
{
foreach (var item in list)
{
serializer.Serialize(writer, item);
break;
}
}
else
{
writer.WriteStartArray();
foreach (var item in list)
serializer.Serialize(writer, item);
writer.WriteEndArray();
}
}
}
public static partial class JsonExtensions
{
public static JsonReader MoveToContent(this JsonReader reader)
{
while ((reader.TokenType == JsonToken.Comment || reader.TokenType == JsonToken.None) && reader.Read())
;
return reader;
}
internal static Type GetListItemType(this Type type)
{
// Quick reject for performance
if (type.IsPrimitive || type.IsArray || type == typeof(string))
return null;
while (type != null)
{
if (type.IsGenericType)
{
var genType = type.GetGenericTypeDefinition();
if (genType == typeof(List<>))
return type.GetGenericArguments()[0];
}
type = type.BaseType;
}
return null;
}
}
It can be used as follows:
var settings = new JsonSerializerSettings
{
// Pass true if you want single-item lists to be reserialized as single items
Converters = { new SingleOrArrayListConverter(true) },
};
var list = JsonConvert.DeserializeObject<List<Item>>(json, settings);
Notes:
The converter avoids the need to pre-load the entire JSON value into memory as a JToken hierarchy.
The converter does not apply to lists whose items are also serialized as collections, e.g. List<string []>
The Boolean canWrite argument passed to the constructor controls whether to re-serialize single-element lists as JSON values or as JSON arrays.
The converter's ReadJson() uses the existingValue if pre-allocated so as to support populating of get-only list members.
Secondly, here is a version that works with other generic collections such as ObservableCollection<T>:
public class SingleOrArrayCollectionConverter<TCollection, TItem> : JsonConverter
where TCollection : ICollection<TItem>
{
// Adapted from this answer https://stackoverflow.com/a/18997172
// to https://stackoverflow.com/questions/18994685/how-to-handle-both-a-single-item-and-an-array-for-the-same-property-using-json-n
// by Brian Rogers https://stackoverflow.com/users/10263/brian-rogers
readonly bool canWrite;
public SingleOrArrayCollectionConverter() : this(false) { }
public SingleOrArrayCollectionConverter(bool canWrite) { this.canWrite = canWrite; }
public override bool CanConvert(Type objectType)
{
return typeof(TCollection).IsAssignableFrom(objectType);
}
static void ValidateItemContract(IContractResolver resolver)
{
var itemContract = resolver.ResolveContract(typeof(TItem));
if (itemContract is JsonArrayContract)
throw new JsonSerializationException(string.Format("Item contract type {0} not supported.", itemContract));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
ValidateItemContract(serializer.ContractResolver);
if (reader.MoveToContent().TokenType == JsonToken.Null)
return null;
var list = (ICollection<TItem>)(existingValue ?? serializer.ContractResolver.ResolveContract(objectType).DefaultCreator());
if (reader.TokenType == JsonToken.StartArray)
serializer.Populate(reader, list);
else
list.Add(serializer.Deserialize<TItem>(reader));
return list;
}
public override bool CanWrite { get { return canWrite; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
ValidateItemContract(serializer.ContractResolver);
var list = value as ICollection<TItem>;
if (list == null)
throw new JsonSerializationException(string.Format("Invalid type for {0}: {1}", GetType(), value.GetType()));
if (list.Count == 1)
{
foreach (var item in list)
{
serializer.Serialize(writer, item);
break;
}
}
else
{
writer.WriteStartArray();
foreach (var item in list)
serializer.Serialize(writer, item);
writer.WriteEndArray();
}
}
}
Then, if your model is using, say, an ObservableCollection<T> for some T, you could apply it as follows:
class Item
{
public string Email { get; set; }
public int Timestamp { get; set; }
public string Event { get; set; }
[JsonConverter(typeof(SingleOrArrayCollectionConverter<ObservableCollection<string>, string>))]
public ObservableCollection<string> Category { get; set; }
}
Notes:
In addition to the notes and restrictions for SingleOrArrayListConverter, the TCollection type must be read/write and have a parameterless constructor.
Demo fiddle with basic unit tests here.
To handle this you have to use a custom JsonConverter. But you probably already had that in mind.
You are just looking for a converter that you can use immediately. And this offers more than just a solution for the situation described.
I give an example with the question asked.
How to use my converter:
Place a JsonConverter Attribute above the property. JsonConverter(typeof(SafeCollectionConverter))
public class SendGridEvent
{
[JsonProperty("email")]
public string Email { get; set; }
[JsonProperty("timestamp")]
public long Timestamp { get; set; }
[JsonProperty("category"), JsonConverter(typeof(SafeCollectionConverter))]
public string[] Category { get; set; }
[JsonProperty("event")]
public string Event { get; set; }
}
And this is my converter:
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System;
namespace stackoverflow.question18994685
{
public class SafeCollectionConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return true;
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
//This not works for Populate (on existingValue)
return serializer.Deserialize<JToken>(reader).ToObjectCollectionSafe(objectType, serializer);
}
public override bool CanWrite => false;
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
}
And this converter uses the following class:
using System;
namespace Newtonsoft.Json.Linq
{
public static class SafeJsonConvertExtensions
{
public static object ToObjectCollectionSafe(this JToken jToken, Type objectType)
{
return ToObjectCollectionSafe(jToken, objectType, JsonSerializer.CreateDefault());
}
public static object ToObjectCollectionSafe(this JToken jToken, Type objectType, JsonSerializer jsonSerializer)
{
var expectArray = typeof(System.Collections.IEnumerable).IsAssignableFrom(objectType);
if (jToken is JArray jArray)
{
if (!expectArray)
{
//to object via singel
if (jArray.Count == 0)
return JValue.CreateNull().ToObject(objectType, jsonSerializer);
if (jArray.Count == 1)
return jArray.First.ToObject(objectType, jsonSerializer);
}
}
else if (expectArray)
{
//to object via JArray
return new JArray(jToken).ToObject(objectType, jsonSerializer);
}
return jToken.ToObject(objectType, jsonSerializer);
}
public static T ToObjectCollectionSafe<T>(this JToken jToken)
{
return (T)ToObjectCollectionSafe(jToken, typeof(T));
}
public static T ToObjectCollectionSafe<T>(this JToken jToken, JsonSerializer jsonSerializer)
{
return (T)ToObjectCollectionSafe(jToken, typeof(T), jsonSerializer);
}
}
}
What does it do exactly?
If you place the converter attribute the converter will be used for this property. You can use it on a normal object if you expect a json array with 1 or no result. Or you use it on an IEnumerable where you expect a json object or json array. (Know that an array -object[]- is an IEnumerable)
A disadvantage is that this converter can only be placed above a property because he thinks he can convert everything. And be warned. A string is also an IEnumerable.
And it offers more than an answer to the question:
If you search for something by id you know that you will get an array back with one or no result.
The ToObjectCollectionSafe<TResult>() method can handle that for you.
This is usable for Single Result vs Array using JSON.net
and handle both a single item and an array for the same property
and can convert an array to a single object.
I made this for REST requests on a server with a filter that returned one result in an array but wanted to get the result back as a single object in my code. And also for a OData result response with expanded result with one item in an array.
Have fun with it.
Just wanted to add to #dbc excellent response above on the SingleOrArrayCollectionConverter. I was able to modify it to use with a stream from an HTTP client. Here is a snippet (you will have to set up the requestUrl (string) and the httpClient (using System.Net.Http;).
public async Task<IList<T>> HttpRequest<T>(HttpClient httpClient, string requestedUrl, CancellationToken cancellationToken)
{
using (var request = new HttpRequestMessage(HttpMethod.Get, requestedUrl))
using (var httpResponseMessage = await httpClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, cancellationToken))
{
if (httpResponseMessage.IsSuccessStatusCode)
{
using var stream = await httpResponseMessage.Content.ReadAsStreamAsync();
using var streamReader = new StreamReader(stream);
using var jsonTextReader = new JsonTextReader(streamReader );
var settings = new JsonSerializerSettings
{
// Pass true if you want single-item lists to be reserialized as single items
Converters = { new SingleOrArrayCollectionConverter(true) },
};
var jsonSerializer = JsonSerializer.Create(settings);
return jsonSerializer.Deserialize<List<T>>(jsonTextReader);
}
I apologize if there are missing brackets or misspellings, it was not easy to paste code in here.
I had a very similar Problem.
My Json Request was completly unknown for me.
I only knew.
There will be an objectId in it and some anonym key value pairs AND arrays.
I used it for an EAV Model i did:
My JSON Request:
{objectId": 2,
"firstName": "Hans",
"email" :[ "a#b.de","a#c.de"],
"name": "Andre",
"something" :["232","123"]
}
My Class i defined:
[JsonConverter(typeof(AnonyObjectConverter))]
public class AnonymObject
{
public AnonymObject()
{
fields = new Dictionary<string, string>();
list = new List<string>();
}
public string objectid { get; set; }
public Dictionary<string, string> fields { get; set; }
public List<string> list { get; set; }
}
and now that i want to deserialize unknown attributes with its value and arrays in it my Converter looks like that:
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
AnonymObject anonym = existingValue as AnonymObject ?? new AnonymObject();
bool isList = false;
StringBuilder listValues = new StringBuilder();
while (reader.Read())
{
if (reader.TokenType == JsonToken.EndObject) continue;
if (isList)
{
while (reader.TokenType != JsonToken.EndArray)
{
listValues.Append(reader.Value.ToString() + ", ");
reader.Read();
}
anonym.list.Add(listValues.ToString());
isList = false;
continue;
}
var value = reader.Value.ToString();
switch (value.ToLower())
{
case "objectid":
anonym.objectid = reader.ReadAsString();
break;
default:
string val;
reader.Read();
if(reader.TokenType == JsonToken.StartArray)
{
isList = true;
val = "ValueDummyForEAV";
}
else
{
val = reader.Value.ToString();
}
try
{
anonym.fields.Add(value, val);
}
catch(ArgumentException e)
{
throw new ArgumentException("Multiple Attribute found");
}
break;
}
}
return anonym;
}
So now everytime i get an AnonymObject i can iterate through the Dictionary and everytime there is my Flag "ValueDummyForEAV" i switch to the list, read the first line and split the values. After that i delete the first entry from the list and go on with iteration from the Dictionary.
Maybe someone has the same problem and can use this :)
Regards
Andre
You can use a JSONConverterAttribute as found here: http://james.newtonking.com/projects/json/help/
Presuming you have a class that looks like
public class RootObject
{
public string email { get; set; }
public int timestamp { get; set; }
public string smtpid { get; set; }
public string #event { get; set; }
public string category[] { get; set; }
}
You'd decorate the category property as seen here:
[JsonConverter(typeof(SendGridCategoryConverter))]
public string category { get; set; }
public class SendGridCategoryConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return true; // add your own logic
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
// do work here to handle returning the array regardless of the number of objects in
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
// Left as an exercise to the reader :)
throw new NotImplementedException();
}
}
You don't need any custom converters, in this case I am usually creating a very simple JsonConstructor
public partial class Item
{
// ... all class properties
[JsonConstructor]
public Item(JToken category)
{
if (category.GetType().Name == "JArray")
Category = category.ToObject<List<string>>();
else
Category = new List<string> { category.ToString() };
}
public Item() { }
}
after this you can deserialize your json using common code
List<Item> items = JsonConvert.DeserializeObject<List<Item>>(json);
I found another solution that can handle the category as string or array by using object. This way I don´t need to mess up with the json serializer.
Please give it a look if you have the time and tell me what you think. https://github.com/MarcelloCarreira/sendgrid-csharp-eventwebhook
It´s based on the solution at https://sendgrid.com/blog/tracking-email-using-azure-sendgrid-event-webhook-part-1/ but I also added date conversion from timestamp, upgraded the variables to reflect current SendGrid model (and made categories work).
I also created a handler with basic auth as option. See the ashx files and the examples.
Thank you!
I always had the impression that the JSON serializer actually traverses your entire object's tree, and executes the custom JsonConverter's WriteJson function on each interface-typed object that it comes across - not so.
I have the following classes and interfaces:
public interface IAnimal
{
string Name { get; set; }
string Speak();
List<IAnimal> Children { get; set; }
}
public class Cat : IAnimal
{
public string Name { get; set; }
public List<IAnimal> Children { get; set; }
public Cat()
{
Children = new List<IAnimal>();
}
public Cat(string name="") : this()
{
Name = name;
}
public string Speak()
{
return "Meow";
}
}
public class Dog : IAnimal
{
public string Name { get; set; }
public List<IAnimal> Children { get; set; }
public Dog()
{
Children = new List<IAnimal>();
}
public Dog(string name="") : this()
{
Name = name;
}
public string Speak()
{
return "Arf";
}
}
To avoid the $type property in the JSON, I've written a custom JsonConverter class, whose WriteJson is
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
JToken t = JToken.FromObject(value);
if (t.Type != JTokenType.Object)
{
t.WriteTo(writer);
}
else
{
IAnimal animal = value as IAnimal;
JObject o = (JObject)t;
if (animal != null)
{
if (animal is Dog)
{
o.AddFirst(new JProperty("type", "Dog"));
//o.Find
}
else if (animal is Cat)
{
o.AddFirst(new JProperty("type", "Cat"));
}
foreach(IAnimal childAnimal in animal.Children)
{
// ???
}
o.WriteTo(writer);
}
}
}
In this example, yes, a dog can have cats for children and vice-versa. In the converter, I want to insert the "type" property so that it saves that to the serialization. I have the following setup. (Zoo has only a name and a list of IAnimals. I didn't include it here for brevity and laziness ;))
Zoo hardcodedZoo = new Zoo()
{ Name = "My Zoo",
Animals = new List<IAnimal> { new Dog("Ruff"), new Cat("Cleo"),
new Dog("Rover"){
Children = new List<IAnimal>{ new Dog("Fido"), new Dog("Fluffy")}
} }
};
JsonSerializerSettings settings = new JsonSerializerSettings(){
ContractResolver = new CamelCasePropertyNamesContractResolver() ,
Formatting = Formatting.Indented
};
settings.Converters.Add(new AnimalsConverter());
string serializedHardCodedZoo = JsonConvert.SerializeObject(hardcodedZoo, settings);
serializedHardCodedZoo has the following output after serialization:
{
"name": "My Zoo",
"animals": [
{
"type": "Dog",
"Name": "Ruff",
"Children": []
},
{
"type": "Cat",
"Name": "Cleo",
"Children": []
},
{
"type": "Dog",
"Name": "Rover",
"Children": [
{
"Name": "Fido",
"Children": []
},
{
"Name": "Fluffy",
"Children": []
}
]
}
]
}
The type property shows up on Ruff, Cleo, and Rover, but not for Fido and Fluffy. I guess the WriteJson isn't called recursively. How do I get that type property there?
As an aside, why does it not camel-case IAnimals like I expect it to?
The reason that your converter is not getting applied to your child objects is because JToken.FromObject() uses a new instance of the serializer internally, which does not know about your converter. There is an overload that allows you to pass in the serializer, but if you do so here you will have another problem: since you are inside a converter and you are using JToken.FromObject() to try to serialize the parent object, you will get into an infinite recursive loop. (JToken.FromObject() calls the serializer, which calls your converter, which calls JToken.FromObject(), etc.)
To get around this problem, you must handle the parent object manually. You can do this without much trouble using a bit of reflection to enumerate the parent properties:
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
JObject jo = new JObject();
Type type = value.GetType();
jo.Add("type", type.Name);
foreach (PropertyInfo prop in type.GetProperties())
{
if (prop.CanRead)
{
object propVal = prop.GetValue(value, null);
if (propVal != null)
{
jo.Add(prop.Name, JToken.FromObject(propVal, serializer));
}
}
}
jo.WriteTo(writer);
}
Fiddle: https://dotnetfiddle.net/sVWsE4
Here's an idea, instead of doing the reflection on every property, iterate through the normally serialized JObject and then changed the token of properties you're interested in.
That way you can still leverage all the ''JsonIgnore'' attributes and other attractive features built-in.
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
JToken jToken = JToken.FromObject(value);
if (jToken.Type == JTokenType.Object)
{
JObject jObject = (JObject)jToken;
...
AddRemoveSerializedProperties(jObject, val);
...
}
...
}
And then
private void AddRemoveSerializedProperties(JObject jObject, MahMan baseContract)
{
jObject.AddFirst(....);
foreach (KeyValuePair<string, JToken> propertyJToken in jObject)
{
if (propertyJToken.Value.Type != JTokenType.Object)
continue;
JToken nestedJObject = propertyJToken.Value;
PropertyInfo clrProperty = baseContract.GetType().GetProperty(propertyJToken.Key);
MahMan nestedObjectValue = clrProperty.GetValue(baseContract) as MahMan;
if(nestedObj != null)
AddRemoveSerializedProperties((JObject)nestedJObject, nestedObjectValue);
}
}
I had this issue using two custom converters for a parent and child type. A simpler method I found is that since an overload of JToken.FromObject() takes a serializer as a parameter, you can pass along the serializer you were given in WriteJson(). However you need to remove your converter from the serializer to avoid a recursive call to it (but add it back in after):
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
serializer.Converters.Remove(this);
JToken jToken = JToken.FromObject(value, serializer);
serializer.Converters.Add(this);
// Perform any necessary conversions on the object returned
}
Here is a hacky solution to your problem that gets the work done and looks tidy.
public class MyJsonConverter : JsonConverter
{
public const string TypePropertyName = "type";
private bool _dormant = false;
/// <summary>
/// A hack is involved:
/// " JToken.FromObject(value, serializer); " creates amn infinite loop in normal circumstances
/// for that reason before calling it "_dormant = true;" is called.
/// the result is that this JsonConverter will reply false to exactly one "CanConvert()" call.
/// this gap will allow to generate a a basic version without any extra properties, and then add them on the call with " JToken.FromObject(value, serializer); ".
/// </summary>
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
_dormant = true;
JToken t = JToken.FromObject(value, serializer);
if (t.Type == JTokenType.Object && value is IContent)
{
JObject o = (JObject)t;
o.AddFirst(new JProperty(TypePropertyName, value.GetType().Name));
o.WriteTo(writer);
}
else
{
t.WriteTo(writer);
}
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
throw new NotImplementedException();
}
public override bool CanRead => false;
public override bool CanConvert(Type objectType)
{
if (_dormant)
{
_dormant = false;
return false;
}
return true;
}
}
So I am needing to serialize a composite to JSON (with JSON.NET) and was hoping that coming here with this problem would be a quick win.
I have a very basic composite implementation that I am just trying to use to scaffold my services and the data structure but the JSONSerializer is only serializing the root node.
Code:
namespace Data
{
public abstract class Element
{
protected string _name;
public Element(string name)
{
_name = name;
}
public abstract void Add(Element element);
public string Name { get { return _name; } }
}
public class ConcreteElement : Element
{
public ConcreteElement(string name) : base(name) { }
public override void Add(Element element)
{
throw new InvalidOperationException("ConcreteElements may not contain Child nodes. Perhaps you intended to add this to a Composite");
}
}
public class Composite: Element
{
public Composite(string name) : base(name) { Elements = new List<Element>(); }
private List<Element> Elements { get; set; }
public override void Add(Element element)
{
Elements.Add(element);
}
}
}
In my Controller's HttpGet method,
Composite root = new Composite("Root");
Composite branch = new Composite("Branch");
branch.Add(new ConcreteElement("Leaf1"));
branch.Add(new ConcreteElement("Leaf2"));
root.Add(branch);
return JsonConvert.SerializeObject(root);
And the only thing that is being serialized is
{"Name\":\"Root\"}"
Can anyone see a reason that this is not serializing child elements?
I'm hoping it's something stupid.
Edit1
I've never tried to Serialize a graph to JSON with WebAPI before. Do I need to write a custom MediaTypeFormatter for serializing this?
Edit2 (to add desired output)
Leaf1 and Leaf2 are just markers at the moment. They will themselves be complex objects once I can get this to serialize.
So, at the moment...
{
"Name" : "Root"
,"Branch":
[
{"Name":"Leaf1"}
,{"Name":"Leaf2"}
]
]
}
and eventually
{
"Name" : "Root"
,"Branch1":
[
{"Name":"Leaf1", "Foo":"Bar"}
{"Name":"Leaf2", "Foo":"Baz"}
]
,"Branch2":
[
"Branch3":[
{"Name":"Leaf3", "Foo":"Quux"}
]
]
}
The children are not being serialized because the list of Elements in your Composite is private. Json.Net will not serialize private members by default. If you mark the list with [JsonProperty("Elements")] then the children will be serialized.
public class Composite: Element
{
...
[JsonProperty("Elements")]
private List<Element> Elements { get; set; }
...
}
If you run your example code with this change, you should get the following JSON:
{
"Elements": [
{
"Elements": [
{
"Name": "Leaf1"
},
{
"Name": "Leaf2"
}
],
"Name": "Branch"
}
],
"Name": "Root"
}
EDIT
OK, here is an example converter for your composite:
class CompositeConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(Composite));
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
Composite composite = (Composite)value;
// Need to use reflection here because Elements is private
PropertyInfo prop = typeof(Composite).GetProperty("Elements", BindingFlags.NonPublic | BindingFlags.Instance);
List<Element> children = (List<Element>)prop.GetValue(composite);
JArray array = new JArray();
foreach (Element e in children)
{
array.Add(JToken.FromObject(e, serializer));
}
JObject obj = new JObject();
obj.Add(composite.Name, array);
obj.WriteTo(writer);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
Here is a demo:
class Program
{
static void Main(string[] args)
{
Composite root = new Composite("Root");
Composite branch1 = new Composite("Branch1");
branch1.Add(new ConcreteElement("Leaf1", "Bar"));
branch1.Add(new ConcreteElement("Leaf2", "Baz"));
root.Add(branch1);
Composite branch2 = new Composite("Branch2");
branch2.Add(new ConcreteElement("Leaf3", "Quux"));
Composite branch3 = new Composite("Branch3");
branch3.Add(new ConcreteElement("Leaf4", "Fizz"));
branch2.Add(branch3);
root.Add(branch2);
string json = JsonConvert.SerializeObject(root, Formatting.Indented, new CompositeConverter());
Console.WriteLine(json);
}
}
public abstract class Element
{
protected string _name;
public Element(string name)
{
_name = name;
}
public abstract void Add(Element element);
public string Name { get { return _name; } }
}
public class ConcreteElement : Element
{
public ConcreteElement(string name, string foo) : base(name)
{
Foo = foo;
}
public string Foo { get; set; }
public override void Add(Element element)
{
throw new InvalidOperationException("ConcreteElements may not contain Child nodes. Perhaps you intended to add this to a Composite");
}
}
public class Composite : Element
{
public Composite(string name) : base(name) { Elements = new List<Element>(); }
private List<Element> Elements { get; set; }
public override void Add(Element element)
{
Elements.Add(element);
}
}
Here is the resulting JSON output:
{
"Root": [
{
"Branch1": [
{
"Foo": "Bar",
"Name": "Leaf1"
},
{
"Foo": "Baz",
"Name": "Leaf2"
}
]
},
{
"Branch2": [
{
"Foo": "Quux",
"Name": "Leaf3"
},
{
"Branch3": [
{
"Foo": "Fizz",
"Name": "Leaf4"
}
]
}
]
}
]
}
I realize that this is not exactly the same JSON that you asked for, but it should get you going in the right direction. One problem with the "desired" JSON you specified in your question is that it is not entirely valid. Named properties can only be inside an object, not directly inside an array. In your second example, you have a named "Branch3" property directly inside the array for "Branch2". This won't work. So, you would need to make Branch2 an object instead. But if you do this, then you have an inconsistent representation for your composite: if it contains only leaves, then it is an array, otherwise it is an object. It is possible to make a converter to change the representation of the composite based on the contents (in fact I managed to create such a beast), but that makes the JSON more difficult to consume, and in the end I don't think you'll want to use it. In case you're curious, I've included this alternate converter below, along with its output.
class CompositeConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(Composite));
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
Composite composite = (Composite)value;
// Need to use reflection here because Elements is private
PropertyInfo prop = typeof(Composite).GetProperty("Elements", BindingFlags.NonPublic | BindingFlags.Instance);
List<Element> children = (List<Element>)prop.GetValue(composite);
// if all children are leaves, output as an array
if (children.All(el => el.GetType() != typeof(Composite)))
{
JArray array = new JArray();
foreach (Element e in children)
{
array.Add(JToken.FromObject(e, serializer));
}
array.WriteTo(writer);
}
else
{
// otherwise use an object
JObject obj = new JObject();
if (composite.Name == "Root")
{
obj.Add("Name", composite.Name);
}
foreach (Element e in children)
{
obj.Add(e.Name, JToken.FromObject(e, serializer));
}
obj.WriteTo(writer);
}
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
Output using the same data:
{
"Name": "Root",
"Branch1": [
{
"Foo": "Bar",
"Name": "Leaf1"
},
{
"Foo": "Baz",
"Name": "Leaf2"
}
],
"Branch2": {
"Leaf3": {
"Foo": "Quux",
"Name": "Leaf3"
},
"Branch3": [
{
"Foo": "Fizz",
"Name": "Leaf4"
}
]
}
}
If you don't want to use Datacontract , i think you have to implement JsonConverter with some the methodes that you need.
namespace JsonOutil
{
public class TestConverter<T> : JsonConverter
{
public override bool CanConvert(System.Type objectType)
{
return objectType == typeof(yourClasse);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
object retVal = new Object();
if (reader.TokenType == JsonToken.StartObject)
{
T instance = (T)serializer.Deserialize(reader, typeof(T));
retVal = new List<T>() { instance };
}
else if (reader.TokenType == JsonToken.StartArray)
{
retVal = serializer.Deserialize(reader, objectType);
}
return retVal;
}
public override object ReadJson(JsonReader reader, System.Type objectType, object existingValue, JsonSerializer serializer)
{
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new System.NotImplementedException();
}
public string GetValueWhenReading(Dictionary<string, object> values, string key)
{
return !values.ContainsKey(key) || values[key] == null
? null
: values[key].ToString();
}
}
}
In the following scenario, how do I get CrazyItemConverter to carry on as usual when it encounters a JSON property that exists in the type I'm deserializing to?
I have some JSON that looks like this:
{
"Item":{
"Name":"Apple",
"Id":null,
"Size":5,
"Quality":2
}
}
The JSON gets deserialized into a class that looks a whole lot like this:
[JsonConverter(typeof(CrazyItemConverter))]
public class Item
{
[JsonConverter(typeof(CrazyStringConverter))]
public string Name { get; set; }
public Guid? Id { get; set; }
[JsonIgnore]
public Dictionary<string, object> CustomFields
{
get
{
if (_customFields == null)
_customFields = new Dictionary<string, object>();
return _customFields;
}
}
...
}
CrazyItemConverter populates the values of the known properties and puts the unknown properties in CustomFields. The ReadJson in it looks like this:
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
var outputObject = Create(objectType);
var objProps = objectType.GetProperties().Select(p => p.Name).ToArray();
while (reader.Read())
{
if (reader.TokenType == JsonToken.PropertyName)
{
string propertyName = reader.Value.ToString();
if (reader.Read())
{
if (objProps.Contains(propertyName))
{
// No idea :(
// serializer.Populate(reader, outputObject);
}
else
{
outputObject.AddProperty(propertyName, reader.Value);
}
}
}
}
return outputObject;
}
During deserialization, when CrazyItemConverter encounters a known property, I want it to act as it normally would. Meaning, respecting the [JsonConverter(typeof(CrazyStringConverter))] for Name.
I was using the code below to set the known properties but, it throws exceptions on nullables and doesn't respect my other JsonConverters.
PropertyInfo pi = outputObject.GetType().GetProperty(readerValue, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);
var convertedValue = Convert.ChangeType(reader.Value, pi.PropertyType);
pi.SetValue(outputObject, convertedValue, null);
Any ideas?
UPDATE: I've learned that serializer.Populate(reader, outputObject); is how to deserialize the whole thing but it doesn't seem to work if you want default functionality on a property-by-property basis.
If I'm understanding correctly, your CrazyItemConverter exists so that you can deserialize known properties in the JSON to strongly-typed properties, while still preserving "extra" fields that may be in the JSON into dictionary.
It turns out that Json.Net already has this feature built in (since 5.0 release 5), so you don't need a crazy converter. Instead, you just need to mark your dictionary with the [JsonExtensionData] attribute. (See the author's blog for more information.)
So your Item class would look like this:
public class Item
{
[JsonConverter(typeof(CrazyStringConverter))]
public string Name { get; set; }
public Guid? Id { get; set; }
[JsonExtensionData]
public Dictionary<string, object> CustomFields
{
get
{
if (_customFields == null)
_customFields = new Dictionary<string, object>();
return _customFields;
}
private set
{
_customFields = value;
}
}
private Dictionary<string, object> _customFields;
}
Then you can just deserialize it as normal. Demo:
class Program
{
static void Main(string[] args)
{
string json = #"
{
""Item"":
{
""Name"":""Apple"",
""Id"":""4b7e9f9f-7a30-4f79-8e47-8b50ea26ddac"",
""Size"":5,
""Quality"":2
}
}";
Item item = JsonConvert.DeserializeObject<Wrapper>(json).Item;
Console.WriteLine("Name: " + item.Name);
Console.WriteLine("Id: " + item.Id);
foreach (KeyValuePair<string, object> kvp in item.CustomFields)
{
Console.WriteLine(kvp.Key + ": " + kvp.Value);
}
}
}
public class Wrapper
{
public Item Item { get; set; }
}
class CrazyStringConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(string);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JToken token = JToken.Load(reader);
// Reverse the string just for fun
return new string(token.ToString().Reverse().ToArray());
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
Output:
Name: elppA
Id: 4b7e9f9f-7a30-4f79-8e47-8b50ea26ddac
Size: 5
Quality: 2