How to combine (OR) two expression trees

Question

我有两种类型的表达式树： Expression<Func<string, bool>> ，我想获得一个单独的Expression，它将对两个表达式进行或运算（将相同的字符串参数传递给两个表达式）。

Answer 1

You can use PredicateBuilder from LINQKit to do this. For example:

Expression<Func<string, bool>> e1 = …;
Expression<Func<string, bool>> e2 = …;
Expression<Func<string, bool>> combined = e1.Or(e2).Expand();

Answer 2

You can try combining them in a Expression.Lambda expression and then using Expression.Or to check if one of them is true.

Here is an example:

Expression<Func<Car, bool>> theCarIsRed = c1 => c1.Color == "Red";
Expression<Func<Car, bool>> theCarIsCheap = c2 => c2.Price < 10.0;
Expression<Func<Car, bool>> theCarIsRedOrCheap = Expression.Lambda<Func<Car, bool>>(
    Expression.Or(theCarIsRed.Body, theCarIsCheap.Body), theCarIsRed.Parameters.Single());
var query = carQuery.Where(theCarIsRedOrCheap);

Maybe you can get more info here