NORM cannot handle lambda expressions where the type is an interface type

[IanMercer]

NORM cannot handle expressions where the type is an interface type.

For example, in a generic class that has an interface constraint on the type, when I access a property of T, e.g. ".UniqueIdentifier" NORM cannot handle the expression and an Exception is thrown (relating to its inability to case a UnaryExpression to a ParameterExpression).

            var existing = db.GetCollection<T>().AsQueryable().SingleOrDefault(x => x.UniqueIdentifier == uid);

In this expression 'x.UniqueIdentifier' has a NodeType=Convert wrapped around it to perform the cast to the interface.

It's actually a fairly simple fix: In MongoQueryTranslator.cs, about line 407 there is an if statement in ...

    private static ParameterExpression GetParameterExpression(Expression expression)

Adding the following clause to the if statement solves the problem:

    ...
            else if (parentExpression.NodeType == ExpressionType.Convert)
            {
                parentExpression = ((UnaryExpression)parentExpression).Operand;
                expressionRoot = parentExpression is ParameterExpression;
            }