user2657943 user2657943 -4 years ago 243
C# Question

AmbiguousMatchException in Expression.PropertyOrField

I am using reflection to create a lambda function. It works with most items I try it with, however on one of the properties it keeps throwing an Ambiguous Match Exception.

The code looks like this. The error happens when it hits

Expression.PropertyOrField
. The property I am using is of type
decimal?
. I think it might have to do with the fact that it is a nullable type, but I'm not sure.

public static LambdaExpression CreateExpression(Type type, string propertyName, ref Type returnType)
{
var param = Expression.Parameter(type, "x");
Expression body = param;
foreach (var member in propertyName.Split('.'))
{
body = Expression.PropertyOrField(body, member);
}
returnType = body.Type;
return Expression.Lambda(body, param);
}

Answer Source

I see only one way such exception might be thrown in this case: you have multiple properties with the same name but different casing, like this:

public class Test {
    public decimal? testProp { get; set; }
    public decimal? TestProp { get; set; }
}

Or fields:

public class Test {
    public decimal? testProp;
    public decimal? TestProp;
}

Note that property with the same name might be in any parent class up hierarchy also:

public class BaseTest {
    public decimal? testProp { get; set; }
}

public class Test : BaseTest {        
    public decimal? TestProp { get; set; } // also fails
}

The reason is Expression.PropertyOrField does this to search for desired property:

type.GetProperty(propertyOrFieldName, BindingFlags.IgnoreCase | BindingFlags.Instance | BindingFlags.Public | BindingFlags.FlattenHierarchy);

Note BindingFlags.IgnoreCase and BindingFlags.FlattenHierarchy. So you cannot tell Expression.PropertyOrField to search in case-sensitive manner.

However I would argue that to have multiple properties with the same name is a bad practice anyway and should be avoided.

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