Following my last post, I received lots of enquiries about how got to master the creation of expression trees.
The answer is: .NET Reflector
On that post I needed to to generate an expression tree for this expression:
Expression<Func<object, object>> expression = o => ((object)((SomeType)o).Property1);
I just compiled that code in Visual Studio 2010, loaded the assembly in .NET Reflector, and disassembled it to C# without optimizations (View –> Options –> Disassembler –> Optimization: None).
The disassembled code looked like this:
Expression<Func<object, object>> expression;
ParameterExpression CS$0$0000;
ParameterExpression[] CS$0$0001;
expression = Expression.Lambda<Func<object, object>>(Expression.Convert(Expression.Property(Expression.Convert(CS$0$0000 = Expression.Parameter(typeof(object), "o"), typeof(SomeType)), (MethodInfo) methodof(SomeType.get_Property1)), typeof(object)), new ParameterExpression[] { CS$0$0000 });
After giving valid C# names to the variables and tidy up the code a bit, I came up with this:
ParameterExpression parameter = Expression.Parameter(typeof(object), "o");
Expression<Func<object, object>> expression =
Expression.Lambda<Func<object, object>>(
Expression.Convert(
Expression.Property(
Expression.Convert(
parameter,
typeof(SomeType)
),
"Property1"
),
typeof(object)
),
parameter
);
Easy! Isn’t it?