Question

I’m looking to take an in-memory object (or JSON serialization of an object) and emit C# code to produce an equivalent object.

This would be useful for pulling known-good examples from a repository to use as starting points in unit tests. We have considered deserializing JSON, but C# code would have an edge when it comes to refactoring.

Answer 1

If your model is simple, you could use reflection and a string builder to output C# directly. I’ve done this to populate unit test data exactly as you discussed.

The code sample below was written in a few minutes and generated an object initializer that needed some hand tweaking. A more robust / less buggy function could be written if you plan on doing this a lot.

The second function is recursive, iterating over any Lists within the object, and generating code for those as well.

Disclaimer: This worked for my simple model with basic data types. It generated code that needed cleanup but allowed me to move on quickly. It is only here to serve as an example of how this could be done. Hopefully, it inspires someone to write their own.

In my case, I had an instance of this large dataset (results) that was loaded from the database. In order to remove the database dependency from my unit test, I handed the object to this function which spits out the code that allowed me to mock the object in my test class.

    private void WriteInstanciationCodeFromObject(IList results)
    {

        //declare the object that will eventually house C# initialization code for this class
        var testMockObject = new System.Text.StringBuilder();

        //start building code for this object
        ConstructAndFillProperties(testMockObject, results);

        var codeOutput = testMockObject.ToString();
    }


    private void ConstructAndFillProperties(StringBuilder testMockObject, IList results)
    {

        testMockObject.AppendLine("var testMock = new " + results.GetType().ToString() + "();");

        foreach (object obj in results)
        {

            //if this object is a list, write code for its contents

            if (obj.GetType().GetInterfaces().Contains(typeof(IList)))
            {
                ConstructAndFillProperties(testMockObject, (IList)obj);
            }

            testMockObject.AppendLine("testMock.Add(new " + obj.GetType().Name + "() {");

            foreach (var property in obj.GetType().GetProperties())
            {

               //if this property is a list, write code for its contents
                if (property.PropertyType.GetInterfaces().Contains(typeof(IList)))
                {
                    ConstructAndFillProperties(testMockObject, (IList)property.GetValue(obj, null));
                }

                testMockObject.AppendLine(property.Name + " = (" + property.PropertyType + ")\"" + property.GetValue(obj, null) + "\",");
            }

            testMockObject.AppendLine("});");
        }
    }