Serialzation Exception when passing parameter from MVC Controller Action

Im getting an exception on expressionSerializer.SerializeText() when trying to serialize an Expression, seemingly when it contains a reference from an MVC action controller. When assign a new local variable in its place with the same value, the serialization succeeds.

Exception Detail Error converting type: Type 'WhiteBox.WebApp.Helpers.ConnectorInstanceHelper+<>c__DisplayClass4_0' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. Alternatively, you can ensure that the type is public and has a parameterless constructor - all public members of the type will then be serialized, and no attributes will be required.

If I inspect the Expression while debugging, i can see the following difference between the local variable

.Constant<Whitebox.WebApp.Helpers.ConnectorInstanceHelper+<>c__DisplayClass4_0>(Whitebox.WebApp.Helpers.ConnectorInstanceHelper+<>c__DisplayClass4_0).productId

and the one being passed from the controller action. The difference being the CS$<>8__locals1 suffix.

.Constant<Whitebox.WebApp.Helpers.ConnectorInstanceHelper+<>c__DisplayClass4_1>(Whitebox.WebApp.Helpers.ConnectorInstanceHelper+<>c__DisplayClass4_1).CS$<>8__locals1).productId

-Visual Studio 2017 -Net CORE 2.2 -Microsoft.AspNetCore.MVC 2.2.0

[gorillapower]

Hi Sascha,

For me the exception is caught and writes “Exception Thrown”. Does the code not enter the Catch()?

On Thu, 25 Apr 2019 at 14:30, Sascha Kiefer [e-mail] wrote:

Is there something else, because if i run this in a console app, it runs without problems

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[gorillapower]

Hi @esskar, sorry for delayed response. I tried to create a test case where i can consistently reproduce the issue. It still seems to be related to the naming I see in the debug view of the expression, but ive narrowed it down it bit further.

If you initiate the code with await new TestClass().TestMethod("1231231"); the code within try-catch will throw an exception. The code after that executes without exception. If you move the `var userId = “12313”;’ outside the try-catch and similarily, if you remove the try-catch altogether (demonstrated by the subsequent code) the code executes fine. Its cases when the CS$<>8__locals1 is present in the expression that the serialization seems to fail.

I also noted that removing the the productId parameter from TestMethod results in no errors.

public class TestClass
    {
        public TestClass() { }

        public async Task TestMethod(string productId)
        {
            try
            {
                var userId = "12313";
                DoSerialization<ProductTest>(x => x.UserId == userId && x.ProductId == productId);
            }
            catch (Exception)
            {
                Trace.WriteLine("Exception thrown");
            }

            var userId2 = "12313";
            DoSerialization<ProductTest>(x => x.UserId == userId2 && x.ProductId == productId);
        }

        public static void DoSerialization<T>(Expression<Func<T, bool>> predicate)
        {
            var expressionSerializer = new ExpressionSerializer(new Serialize.Linq.Serializers.JsonSerializer());
            var queryJson = expressionSerializer.SerializeText(predicate);
        }
    }
    public class ProductTest
    {
        public string ProductId { get; set; }

        public string UserId { get; set; }
    }

    public class UserTest
    {
        public string Email { get; set; }
        public string UserId { get; set; }
    }