Develop Reference

Overriding a base virtual property with a derived type is null when passing to JsonResult

I have 2 base classes which 1 for search criteria and other 1 for search results.
I also have 2 derived classes for User object versions of both of those.
When I put a breakpoint in the controller action I can see all properties are populated as I've hardcoded.
When I call this action directly in the browser, each of my derived object properties is null.
I'm guessing the JSON serialization is not able to tell the difference from the base class to the derived one.
Is there a way to solve this?
public class BaseSearchCriteria
{
public int Page { get; set; }
public int RecordsPerPage { get; set; }
}
public class BaseSearchResults
{
public int TotalResults { get; set; }
public virtual BaseSearchCriteria SearchCriteria { get; set; }
}
public class UserSearchCriteria : BaseSearchCriteria
{
public string Username { get; set; }
}
public class UserSearchResults : BaseSearchResults
{
public new UserSearchCriteria SearchCriteria { get; set; }
}
public JsonResult Search(UserSearchCriteria model)
{
var viewModel = new UserSearchResults
{
SearchCriteria = new UserSearchCriteria
{
Page = 1,
RecordsPerPage = 15
}
};
viewModel.TotalResults = 100;
return Json(viewModel, JsonRequestBehavior.AllowGet);
}

Maybe good way to deal with it is to use generics as Daniel A. White propose.
Sample gist here.

Need solution regarding generic c# method

I am trying to make my method generic and I am stuck at a point and need your assistance. The code scenario is I have an abstract class say MyBaseAbs which contains common properties:
public abstract class MyBaseAbs
{
public string CommonProp1 { get; set; }
public string CommonProp2 { get; set; }
public string CommonProp3 { get; set; }
}
Now I have child classes:
public class Mychild1: MyBaseAbs
{
public string Mychild1Prop1 { get; set; }
public string Mychild1Prop2 { get; set; }
public string Mychild1Prop3 { get; set; }
}
and another child class:
public class Mychild2: MyBaseAbs
{
public string Mychild1Prop1 { get; set; }
public string Mychild2Prop2 { get; set; }
}
Now I have to create a common method which needs to perform some operations on the basis of Mychild1 and Mychild2, so what I did is:
public MyCustomClass SaveOperation<T>(T myObj)
where T : MyBaseAbs
{
SaveObject obj = new SaveObject();
}
so inside this method I need to write common code which does the mapping for SaveObject object according to the child object passed. How can I determine which object is passed and use properties accordingly.

One option would be to create a base Save function in your base class and make it virtual.
Then override the method in your child classes. This way when you call the Save method in your SaveOperation it should call the appropriate method from the correct child class.
public abstract class MyBaseAbs
{
public string CommonProp1 { get; set; }
public string CommonProp2 { get; set; }
public string CommonProp3 { get; set; }
public virtual void Save() { }
}
public class Mychild1: MyBaseAbs
{
public string Mychild1Prop1 { get; set; }
public string Mychild1Prop2 { get; set; }
public string Mychild1Prop3 { get; set; }
public override void Save() {
//Implementation for Mychild1
}
}
public class Mychild2: MyBaseAbs
{
public string Mychild1Prop1 { get; set; }
public string Mychild2Prop2 { get; set; }
public override void Save() {
//Implementation for Mychild2
}
}

If you can't modify your business objects, you can check the type of the concrete class in the SaveOperation method:
public MyCustomClass SaveOperation<T>(T myObj)
where T : MyBaseAbs
{
SaveObject obj = new SaveObject();
if (myObj is Mychild1) {
Mychild1 mychild1 = (Mychild1) myObj;
// Business logic for object of type Mychild1
} else if (myObje is Mychild2) {
Mychild2 mychild2 = (Mychild2) myObj;
// Business logic for object of type Mychild2
}
}
Notice that this is not a very solid solution as, if you are creating new objects that implement your abstract class, you will have to remeber to add another branch in the if statement.

As #BojanB mentioned, the obvious solution would be to create a virtual method in your base class and override it in the derived, but if you cannot modify the code there then you can create a method for each derived class and create a dictionary that maps each type to its method:
private Dictionary<Type, Action<MyBaseAbs, MyCustomClass>> _saveOperations =
new Dictionary<Type, Action<MyBaseAbs, MyCustomClass>>();
//You can then set an entry for each of your derived classes
_saveOperations[typeof(Mychild1)] = (myObj, myCustomObj) =>
{
//Mychild1-specific logic
};
public MyCustomClass SaveOperation(MyBaseAbs obj)
{
//do the common saving operations here
var result = new MyCustomClass();
//....
var actualType = obj.GetType();
if(_saveOperations.ContainsKey(actualType))
{
_saveOperations[actualType](obj, result);
}
return result;
}
You can then add an item to the dictionary for each derived class. It is the same concept as using the is operator but allows you to add methods for more derived types without modifying the original SaveOperation method

You can use C#'s As-Operator as follows:
Mychild1 child1 = myObj as Mychild1;
if(child1 != null) {
//Here you can use child1.Mychild1Prop1 forexample
}
Link to msdn: https://msdn.microsoft.com/en-us/library/cscsdfbt.aspx

Returning an object derived from an interface with generic list

My application reads in JSON from disk and deserialising using JSON.net; which is working fine.
My JSON is laid out like this:
{
"driver": {
"driverTag": "blah_blah",
"driverName": "Blah Blah",
"driverTransport": "serial-device"
},
"devices": [
{
"deviceName": "Dev1",
"deviceTag": "DEV1",
"deviceStartMode": "Auto"
},
{
"deviceName": "Dev2",
"deviceTag": "DEV2",
"deviceStartMode": "Auto"
}
]
}
Based on the "driverTransport" value, I deserialise to either a SerialDriverConfig, TelnetDriverConfig, SNMPDriverConfig... etc class.
As the "driver" properties will be the same for every driver, no matter the transport type, I have a "DriverConfigTemplate" class. The "devices" will differ from JSON file to JSON file and have specific properties for that transport type (i.e. a serial device will have properties like "serialPortName", "serialBaudRate" etc.)
I have a "DriverConfig" interface, where T is "DeviceConfig".
public interface DriverConfig<T> where T : DeviceConfig
{
DriverConfigTemplate driver { get; set; }
List<T> devices { get; set; }
}
My device config is as follows:
public class DeviceConfig : IDeviceConfig
{
public string deviceTag { get; set; }
public string deviceName { get; set; }
public string deviceStartMode { get; set; }
}
Now; the problem part. When I am deserialising, I check the transport type before hand and determine the class to use; i.e for a serial driver I will use the "SerialDriverConfig" class and deserialise using the "SerialDeviceConfig":
public class SerialDeviceConfig : DeviceConfig
{
public int serialComPort { get; set; }
public int serialBaudRate { get; set; }
public int serialDataBits { get; set; }
public string serialParity { get; set; }
public string serialStopBits { get; set; }
public string serialHandshake { get; set; }
public int serialReadTimeout { get; set; }
public int serialWriteTimeout { get; set; }
public bool serialRtsEnable { get; set; }
public bool serialDtrEnable { get; set; }
}
My "SerialDriverConfig" class looks like this:
public class SerialDriverConfig : DriverConfig<SerialDeviceConfig>
{
public DriverConfigTemplate driver { get; set; }
public List<SerialDeviceConfig> devices { get; set; }
}
Again, this is fine and the JSON.net deserialiser does its job perfectly.
I have a function that gets called when the JSON config file has been loaded and validated against its respective schema, then passed on to a "DeserialiseDriverConfig" function where I am trying to return the derived driver object; which is where I am stuck :(
private DriverConfig<DeviceConfig> DeserialiseDriverConfig(string _json, string _driverTransport)
{
switch (_driverTransport)
{
case "serial-device":
try
{
SerialDriverConfig _serialDriverConfig = JsonConvert.DeserializeObject<SerialDriverConfig>(_json);
if (_serialDriverConfig != null)
{
return _serialDriverConfig;
}
}
catch (Exception e)
{
//Blah blah blah
}
break;
}
return null;
}
I have been stuck on this one for a few days, have tried many things and this is where I have ended up. I am getting "Cannot implicitly convert type "SerialDriverConfig" to "DriverConfig". An explicit conversion exists (are you missing a cast?)" So I understand why this error is occurring, but cannot get around it.
Hope my code makes sense and someone can help me out here?

You can change your DriverConfig class to be non-generic
public interface DriverConfig
{
DriverConfigTemplate driver { get; set; }
List<DeviceConfig> devices { get; set; }
}
and instead of using derived classes (SerialDriverConfig etc.) you can set Json.net to deserialize to the correct DeviceConfig type based on either having a $type attribute in your JSON like this or using a custom JsonConverter similar to this

I'm not sure if this solution fits your need but if you create your method and SerialDriverConfig with using generic type T you can use your interface as a returning type. Can you try the code below;
Your Method:
private static DriverConfig<T> DeserialiseDriverConfig<T>(string _json, string _driverTransport)
{
switch (_driverTransport)
{
case "serial-device":
try
{
SerialDriverConfig<T> _serialDriverConfig = JsonConvert.DeserializeObject<SerialDriverConfig<T>>(_json);
if (_serialDriverConfig != null)
{
return _serialDriverConfig;
}
}
catch (Exception e)
{
//Blah blah blah
}
break;
}
return null;
}
SerialDriverConfig Class:
public class SerialDriverConfig<T> : DriverConfig<T>
{
public DriverConfigTemplate driver { get; set; }
public List<T> devices { get; set; }
}
Also you should consider changing DriverConfig<T> interface approach because if you leave it as-is you will have boxing issue. If you do not need you may remove where T : DeviceConfig from your interface or modify it according to your current circumstances.
Hope this helps, please let me know if this works for you

Get a variable from a class that inherits another

I have an arbitrary amount of classes, classThatInherits, anotherClassThatInherits, etc. that inherit classToBeInherited.
I then have a method, b, that needs to be able to access myValue from the classes that inherit classToBeInherited. How can I achieve this, without casting?
//This class will be inherited by other classes
public class classToBeInherited {
public bool isSomething { get; set; }
}
//This class with inherit 'classToBeInherited'
public class classThatInherits : classToBeInherited {
public int myValue { get; set; } //this needs to be accessable...
}
//...And so will this class
public class anotherClassThatInherits : classToBeInherited {
public int myValue { get; set; }
}
private class normalClass {
private void a() {
classThatInherits cti = new classThatInherits();
b(cti);
anotherClassThatInherits acti = new anotherClassThatInherits();
b(acti);
}
private void b(classToBeInherited c) {
//***
//get myValue from the classes that inherit classToBeInherited
//***
}
}

Move myValue to classToBeInherited:
public class classToBeInherited {
public bool isSomething { get; set; }
public abstract int myValue { get; set; }
}
Then in classThatInherits and anotherClassThatInherits use public override int myValue { get; set; } to implement that property.
Ofcorse, if myValue is needed in only some of the classes, then you can have virtual and not abstract property.

var a = c as anotherClassThatInherits;
if (a != null)
{
var myValue = a.myValue;
}
I don't know why you don't want to do casting, but it's very common to have code like above.
UPDATED
If you really don't want casting, you can use reflection (but you still need to know the type of anotherClassThatInherits)
var getter = typeof(anotherClassThatInherits).GetProperty("myValue").GetGetMethod();
var myValue = getter.Invoke(c, null);

How use the same method for different classes as parameter

I've got a function with List<> set as the parameter, which looks something like this:
private Double CalculateConsumption(List<GasConsumRecord> gasRecord)
{
...
foreach (var record in gasRecords){
var x = record.Counter;
var y = record.Pressure;
...
}
...
}
GasConsumRecord class has more properties but in this function I use only 2.
And I've got another class - AirConsumRecord which has the same 2 properties but other properties are different. Both classes have only properties, but no methods.
My question is: How can I use the same method for two different class List<> as parameter?
Thanks in advance.

You'll need your classes to implement the same interface, or derive from the same base class, which contains these two properties, then use a generic method with a type constraint:
If you use interfaces:
public interface IRecord {
int Counter { get; set; }
int Pressure { get; set; }
}
public class GasConsumRecord : IRecord {
public int Counter { get; set; }
public int Pressure { get; set; }
}
public class AirConsumRecord : IRecord {
public int Counter { get; set; }
public int Pressure { get; set; }
}
private Double CalculateConsumption<T>(List<T> records)
where T : IRecord
{
foreach (IRecord record in records){
var x = record.Counter;
var y = record.Pressure;
}
}