Question

I have this method

public Expression<Func<Auction, bool>> GetUnsetDatesAuctionsExpression()
        {
            if (condition)
                return GetAllUnsetDatesAuctionsExpression();
            else
                return (a =>
                        (membershipUser.ProviderUserKey != null) &&
                        (a.OwnerReference == (Guid)membershipUser.ProviderUserKey) &&
                        ((a.Starts == null) || (a.Ends == null)));
            }
        }

which calls this method

private Expression<Func<Auction, bool>> GetAllUnsetDatesAuctionsExpression()
        {
            return (a => (a.Starts == null) || (a.Ends == null));
        }

The issue is that in the above public method I have the below line

(a.Starts == null) || (a.Ends == null)

which is the same as the body of the expression in the private method.

Now, doing this, of course, does not work because you can’t AND a bool and an Expression

return (a =>
   (membershipUser.ProviderUserKey != null) &&
   (a.OwnerReference == (Guid)membershipUser.ProviderUserKey) &&
   (GetAllUnsetDatesAuctionsExpression));

So, the question is, how do I combine the call to the private method with

(membershipUser.ProviderUserKey != null) &&
   (a.OwnerReference == (Guid)membershipUser.ProviderUserKey)

Answer 1

Create a new expression as a combination of the two, see BinaryExpression:

System.Linq.Expressions.BinaryExpression binaryExpression =
  System.Linq.Expressions.Expression.MakeBinary(
    System.Linq.Expressions.ExpressionType.AndAlso,
    firstExpression,
    secondExpression);