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POJSon.Net Serialize result of yield return
 

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    <p>I am trying to return some data to a webservice using json and the JSon.Net library. One of my functions is an iterator method that lists data using yield return. When I try to serialize this return value, I am getting an invalid operation exception </p> <p>I am using <code>string jsonEncoded = JsonConvert.SerializeObject(ret, Formatting.Indented);</code> to serialize the return value. </p> <p>The full stack trace of the exception is:</p> <pre><code>System.InvalidOperationException: This operation is only valid on generic types. at System.RuntimeType.GetGenericTypeDefinition() at Newtonsoft.Json.Serialization.JsonArrayContract..ctor(Type underlyingType) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\JsonArrayContract.cs:line 148 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateArrayContract(Type objectType) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\DefaultContractResolver.cs:line 686 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateContract(Type objectType) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\DefaultContractResolver.cs:line 800 at Newtonsoft.Json.Serialization.DefaultContractResolver.ResolveContract(Type type) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\DefaultContractResolver.cs:line 232 at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.GetContractSafe(Object value) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\JsonSerializerInternalWriter.cs:line 83 at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\JsonSerializerInternalWriter.cs:line 67 at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\JsonSerializer.cs:line 753 at Newtonsoft.Json.JsonSerializer.Serialize(JsonWriter jsonWriter, Object value, Type objectType) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\JsonSerializer.cs:line 668 at Newtonsoft.Json.JsonConvert.SerializeObject(Object value, Type type, Formatting formatting, JsonSerializerSettings settings) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\JsonConvert.cs:line 921 at Newtonsoft.Json.JsonConvert.SerializeObject(Object value, Formatting formatting, JsonSerializerSettings settings) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\JsonConvert.cs:line 893 at Newtonsoft.Json.JsonConvert.SerializeObject(Object value, Formatting formatting) in c:\Temp\Json\Working\Newtonsoft.Json\Src\Newtonsoft.Json\JsonConvert.cs:line 837 at AladdinWeb.Handlers.AladdinHandler.ProcessRequest(HttpContext context) in C:\Users\mehrlich\Projects\AladdinWeb\AladdinWeb\Server\Handlers\AladdinHandler.cs:line 85 [ 15/04/2013 11:24:24.68135 ] </code></pre> <p>The signature of the iterator method is: </p> <pre><code>public IEnumerable&lt;dynamic&gt; FunctionName() { ... } </code></pre> <p>As of now, I have a temporary solution in place by checking for calls to this function and calling <code>ToList</code> on the return value. This serializes just fine, but it is kind of an ugly solution since I need to have a special case for it (and any other iterator methods I might add). My guess is that this has to do with the IEnumerable not being enumerated.</p> <p>Can I get Json.Net to serialize the result of my iterator functions or will I always need a special case like this? Let me know if any more information or source code is needed and I will post it.</p> <p>More Info: I am using the .Net framework version 4.0 and I am using Json.Net version 5.0r2</p> <h2>Abridged Source Code of the Iterator Method</h2> <pre><code>public IEnumerable&lt;dynamic&gt; FunctionName() { var methodList = typeof(Targets).GetMethods(); foreach (var m in methodList) { dynamic info = new ExpandoObject(); info.Name = m.Name; info.Parameters = from param in m.GetParameters() select param.Name; yield return info; } } </code></pre> <h2>Source Code of Method Call</h2> <pre><code>... object ret = null; if (q == "FunctionName") { ret = FunctionName(); // This causes an exception to be thrown later // ret = FunctionName().ToList(); // This does NOT throw an exception later } else { ret = DoOtherStuff(q, request); } // Serialize the result to JSON // This line throws the exception string jsonEncoded = JsonConvert.SerializeObject(ret, Formatting.Indented); ... </code></pre>
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    1. COI'm not sure you can call serialise on that type of iterator method. Do you not know the type that FunctionName returns at compile time? Also calling ToList() I assume you then cast to a specific type at that point?
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    2. COhttp://stackoverflow.com/questions/5156664/how-to-flatten-an-expandoobject-returned-via-jsonresult-in-asp-net-mvc - it may just be a problem that JSON.Net has dealing with dynamic objects; they can be flattened to dictionaries, at which point your problem may go away.
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    3. CO@TheKingDave Do you mean that I cannot serialize `IEnumerable<dynamic>`? I have tried changing the function to `IEnumerable<ExpandoObject>` as well and it didn't change anything. As for the second part, no I am not casting, I simply call `object ret = FunctionName().ToList()`
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