Useful LINQ Method- GetMemberTypeChain

Published 06 March 08 11:18 PM | MattManela 

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:

 

   1: private List<Type> GetMemberTypeChain(Expression expression, bool ignoreCompilerGeneratedTypes)
   2: {
   3:     if (expression == null) return null;
   4:     if (expression.NodeType == ExpressionType.MemberAccess)
   5:     {
   6:         MemberExpression memberExpression = (MemberExpression)expression;
   7:         var result = GetMemberTypeChain(memberExpression.Expression, ignoreCompilerGeneratedTypes);
   8:         Type type = memberExpression.Type;
   9:         if (!(ignoreCompilerGeneratedTypes && IsCompilerGeneratedType(type)))
  10:             result.Add(type);
  11:         return result;
  12:     }
  13:     else if (expression.NodeType == ExpressionType.Constant || expression.NodeType == ExpressionType.Parameter)
  14:     {
  15:         var typeList = new List<CustomTypeInfo>();
  16:         Type type = expression.Type;
  17:         if (!(ignoreCompilerGeneratedTypes && IsCompilerGeneratedType(type)))
  18:             typeList.Add(type);
  19:         return typeList;
  20:     }
  21:     else
  22:     {
  23:         throw new NotSupportedException("Expression type not supported: " + expression.GetType().FullName);
  24:     }
  25: }
  26:  
  27: private bool IsCompilerGeneratedType(Type type)
  28: {
  29:     var compilerGenerateds = type.GetCustomAttributes(typeof(CompilerGeneratedAttribute), true);
  30:     return (compilerGenerateds != null && compilerGenerateds.Length > 0);
  31: }
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# MSDN Blog Postings » Useful LINQ Method- GetMemberTypeChain said on March 7, 2008 3:02 AM:

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About MattManela

I am a software developer at Microsoft. My blog is http://blogs.msdn.com/matt
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