Compare PropertyInfo from Type.GetProperties() and lambda expressions

Question

While creating my testing framework I've found a strange problem. I want to create a static class that would allow me to compare objects of the same type by their properties, but with possibility to ignore some of them. I want to have a simple fluent API for this, so a call like `TestEqualityComparer.Equals(first.Ignore(x=>x.Id).Ignore(y=>y.Name), second);` will return true if the given objects are equal on every property except `Id` and `Name` (they will not be checked for equality). Here goes my code. Of course it's a trivial example (with some obvious overloads of methods missing), but I wanted to extract the simplest code possible. The real case scenario's a bit more complex, so I don't really want to change the approach. The method `FindProperty` is almost a copy-paste from AutoMapper library. Object wrapper for fluent API: ``` public class TestEqualityHelper { public List IgnoredProps = new List(); public T Value; } ``` Fluent stuff: ``` public sta…

Accepted Answer

The reason `FindProperty` is telling you the reflected `Type` is `Base` is because that's the class the lambda would use for the invocation.

You probably know this :)

Instead of GetProperties() from Type, could you use this

```
static IEnumerable<PropertyInfo> GetMappedProperties(Type type)
{
  return type
    .GetProperties()
    .Select(p => GetMappedProperty(type, p.Name))
    .Where(p => p != null);
}

static PropertyInfo GetMappedProperty(Type type, string name)
{
  if (type == null)
    return null;

var prop = type.GetProperty(name);

if (prop.DeclaringType == type)
    return prop;
  else
    return GetMappedProperty(type.BaseType, name);
}
```

To explain more about why the lambda is actually using the Base method directly, and you see essentially a different PropertyInfo, might be better explained looking at the IL

Consider this code:

```
static void Foo()
{
  var b = new Base { Id = 4 };
  var d = new Derived { Id = 5 };

decimal dm = b.Id;
  dm = d.Id;
}
```

And here is the IL for b.Id

```
IL_002f: callvirt instance valuetype [mscorlib]System.Decimal ConsoleApplication1.Base::get_Id()
```

And the IL for d.Id

```
IL_0036: callvirt instance valuetype [mscorlib]System.Decimal ConsoleApplication1.Base::get_Id()
```

Compare PropertyInfo from Type.GetProperties() and lambda expressions

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