Recently, I have been working on a custom LINQ provider in C#.  In a later post (when I have more time to write) I will go in depth into what I am worked on and what have I learned about writing a LINQ provider.  But for now I will present a simple function that simplified part of my work.  It is called GetMemberTypeChain (not as bad as it sounds).  Given a member access expression it will return the types of all parts of the member access chain.  What this means is that given some expression like “myObject.FieldA.FiledB” it will return a list containing the type of each field/property.

In addition to this the method also allows you to filter out compiler created types.  When you have a member access which is using a parameter from a FROM clause in a LINQ query the compiler will often createone or more anonymous type.  Then unknowlingly the object you are trying to access now has a few anonymous field accesses in front of it.  For my purposes I wanted to be able to easily just analyze the types of the relevant parts of the expression.

So without further adieu … GetMemberTypeChain:

private List<Type> GetMemberTypeChain(Expression expression, bool ignoreCompilerGeneratedTypes)
{
    if (expression == null) return null;
    if (expression.NodeType == ExpressionType.MemberAccess)
    {
        MemberExpression memberExpression = (MemberExpression)expression;
        var result = GetMemberTypeChain(memberExpression.Expression, ignoreCompilerGeneratedTypes);
        Type type = memberExpression.Type;
        if (!(ignoreCompilerGeneratedTypes && IsCompilerGeneratedType(type)))
            result.Add(type);
        return result;
    }
    else if (expression.NodeType == ExpressionType.Constant || expression.NodeType == ExpressionType.Parameter)
    {
        var typeList = new List<CustomTypeInfo>();
        Type type = expression.Type;
        if (!(ignoreCompilerGeneratedTypes && IsCompilerGeneratedType(type)))
            typeList.Add(type);
        return typeList;
    }
    else
    {
        throw new NotSupportedException("Expression type not supported: " + expression.GetType().FullName);
    }
}

private bool IsCompilerGeneratedType(Type type)
{
    var compilerGenerateds = type.GetCustomAttributes(typeof(CompilerGeneratedAttribute), true);
    return (compilerGenerateds != null && compilerGenerateds.Length > 0);
}