Develop Reference

MongoDb - cursor option is required after upgrade of mongodb

Since we were forced to upgrade our mongo installation, we're receiving an error during some aggregation function calls:
MongoDB.Driver.MongoCommandException: "Command 'aggregate' failed: The
'cursor' option is required, except for aggregate with the explain
argument (response: { "ok" : 0.0, "errmsg" : "The 'cursor' option is
required, except for aggregate with the explain argument", "code" : 9,
"codeName" : "FailedToParse" })"
BsonArray arr = BsonSerializer.Deserialize<BsonArray>("[{ \"$match\" : { \"Param1\" : \"VAL\" } }, { \"$unwind\" : \"$Entries\" }, { \"$match\" : { \"PARAM\" : \"VALUE\" } }]");
var pipeline = arr.Select(x => x.AsBsonDocument).ToList();
// AggregateArgs aArgs = new AggregateArgs { Pipeline = bsonList };
var cursor = collection.Aggregate(pipeline).ResultDocuments;
I already figured out, that we have to manually add cursor configuration to the BsonDocument - but we weren't able to figure out, how the query should be configured.
Is there any work around for this exception (without changing drivers)?

give this a shot:
var cursor = collection.Aggregate<BsonDocument>(pipeline);
var results = cursor.ToList(); //just get a list of documents and be done with it
while (cursor.MoveNext()) // or iterate over cursor
{
foreach (var doc in cursor.Current.ToArray())
{
//access your documents here
}
}

You have extra brace in the end of query string

was finally able to fix it, by building the command by myself:
var cmd = new CommandDocument()
{
{"aggregate", "collection_name" },
{"pipeline", arr},
{"cursor", BsonDocument.Parse("{}") }
};
var res = db.RunCommand(cmd);

This is what worked in my situation (mongocshardriver v1.9.0-rc0, mongodb server 4.4.0); OutputMode = AggregateOutputMode.Cursor in the AggregateArgs.
public IEnumerable<BsonDocument> Run(MongoCollection<Item> items)
{
var priceRange = new BsonDocument(
"$subtract",
new BsonArray
{
"$Price",
new BsonDocument(
"$mod",
new BsonArray{"$Price", 100})
});
var grouping = new BsonDocument(
"$group",
new BsonDocument
{
{"_id", priceRange},
{"count", new BsonDocument("$sum", 1)}
});
var sort = new BsonDocument(
"$sort",
new BsonDocument("_id", 1)
);
var args = new AggregateArgs
{
Pipeline = new[] { grouping, sort },
OutputMode = AggregateOutputMode.Cursor,
};
return items.Aggregate(args);
}

How do I represent an "empty object" for MongoDB .NET Driver?

I am trying to retrieve index statistics using the MongoDB .NET Driver.
I have tried the following variations of my pipeline
var statsPipeline = new[] { new BsonDocument(new BsonElement("$indexStats", BsonNull.Value)) };
var statsPipeline = new[] { new BsonDocument { {"$indexStats", "" } } };
var statsPipeline = new[] { new BsonDocument { {"$indexStats", null } } };
var statsPipeline = new[] { new BsonDocument { {"$indexStats", BsonNull.Value } } };
var statsPipeline = new[] { new BsonDocument { {"$indexStats", "{ }"} } };
which is passed to the query
var stats = await db
.GetCollection<BsonDocument>("CollectionName")
.AggregateAsync<BsonDocument>(statsPipeline);
With the exception of the one containing null, which resulted in an ArgumentNullException, I have received the exception
MongoDB.Driver.MongoCommandException: Command aggregate failed: The $indexStats stage specification must be an empty object.
How do I change my query such that the $indexStats stage specification is indeed an empty object?

Ok, this one worked:
var statsPipeline = new[] { new BsonDocument(new BsonElement("$indexStats", new BsonDocument())) };

c# Json Deserialization expression

maybe someone know the solution. I can't deserialize expression.
Client side:
var expresion= (Expression<Func<Company, bool>>)(model => model.Id ==id);
var respond = new JObject();
respond .Add("Expression", JToken.FromObject(expresion));
Server side:
JsonSerializer serializer = new JsonSerializer();
serializer.ConstructorHandling = ConstructorHandling.AllowNonPublicDefaultConstructor;
T p = (T)serializer.Deserialize(new JTokenReader(jObject), typeof(T));
Exception:
{"Unable to find a constructor to use for type System.Linq.Expressions.Expression`1[System.Func`2[HostStorageModels.Company,System.Boolean]]. A class should either have a default constructor, one constructor with arguments or a constructor marked with the JsonConstructor attribute. Path 'Expression.Type'."}

I think that it is explicitly telling you that there is no constructor to build the Expression. If you check Expression Constructor () in the MSDN documentation, you will see that it is protected. You could try to send the expression in other serializable format and re build it when you receive it at the other side.

https://github.com/6bee/Remote.Linq
var query = (Expression<Func<Person, bool>>)(model => model.FirstName == "test2");
var remoteExpression = query.ToRemoteLinqExpression();
var request = new Request<Person>
{
Items = new List<Person>()
{
new Person() { FirstName = "test", Id = 1 },
new Person() { FirstName = "test2", Id = 2 }
},
Expression = remoteExpression
};
var serializerSettings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.Auto };
string jsonString = JsonConvert.SerializeObject(request, serializerSettings);
var result = JsonConvert.DeserializeObject<Request<Person>>(jsonString, serializerSettings);
var expresion = result.Expression.ToLinqExpression<Person, bool>();
var filtered = request.Items.Where(expresion.Compile()).ToList();

Creating C# Objects Dynamically

Currently having an issue creating a reusable object that I will need to use in a JSON construct string function.
Currently I have the following to create the bulk of the JSON string:
var data = new
{
record = new
{
value1 = Row.value1,
value2 = Row.value2,
form_values = new Dictionary<string, string>()
}
};
data.record.form_values["833b"] = Row.value3.ToString();
data.record.form_values["98wq"] = BuildMultiSelectList(Row.value3.ToString());
public object BuildMultiSelectList(string datavalue)
{
var choicelist = new {
choice_values: [datavalue],
other_values: [],
};
return choicelist;
}
The top half all works fine, though the function BuildMultiSelectList is giving errors such as "choice_values" does not exist in the current context and datavalue does not exist in the current context.
Any insight on why this has gone a bit rouge will be appreciated.

May be you are just mixing colon : with =?
var choicelist = new {
choice_values = new string[] {datavalue},
other_values = new[] {},
};

C# dynamic ExpandoObject Array

please tell me, how do I get the json like this:
dynamic packet = new ExpandoObject();
packet.type = "somethink";
packet.user = 12345;
packet.nets[0].amout = 123;
packet.nets[0].lower = 0;
packet.nets[1].amout = 345;
packet.nets[1].lower = 1;
string input = Newtonsoft.Json.JsonConvert.SerializeObject(packet);
Its not workig, error:
An unhandled exception of type "Microsoft.CSharp.RuntimeBinder.RuntimeBinderException" in System.Core.dll
For more information: "System.Dynamic.ExpandoObject" does not contain definitions of "nets"
Thanks.

It's the ExpandoObject who's a dynamic object. The rest of properties should be other ExpandoObject instances or regular objects, arrays, collections...
For example:
packet.nets = new[]
{
new { amount = 123, lower = 0 },
new { amount = 345, lower = 1 }
}
Or:
packet.nets = new[]
{
new Dictionary<string, int> { { "amount", 345 }, { "lower", 0 } },
new Dictionary<string, int> { { "amount", 123 }, { "lower", 1 } }
}
There're many other approaches, including the use of instances of concrete classes.

Firstly, you need create nets in packet object, like this:
packet.nets = new dynamic[2];
And initialize the objects in nets, if you want with `ExpandoObject too:
packet.nets[0] = new ExpandoObject();
packet.nets[1] = new ExpandoObject();
Then is done, complete code:
dynamic packet = new ExpandoObject();
packet.type = "somethink";
packet.user = 12345;
packet.nets = new dynamic[2];
packet.nets[0] = new ExpandoObject();
packet.nets[0].amout = 123;
packet.nets[0].lower = 0;
packet.nets[1] = new ExpandoObject();
packet.nets[1].amout = 345;
packet.nets[1].lower = 1;
string input = Newtonsoft.Json.JsonConvert.SerializeObject(packet);

You first need to declare nets. For example
packet.nets = new Dictionary<int, dynamic>();
Then you'll need to instantiate the instances of nets
packet.nets[0] = new {amount = 123, lower = 0};
The result being
dynamic packet = new ExpandoObject();
packet.type = "somethink";
packet.user = 12345;
packet.nets = new Dictionary<int, dynamic>();
packet.nets[0] = new { amount = 123, lower = 0 };
packet.nets[1] = new { amount = 345, lower = 1 };