Predicate build with NET Core and EF Core

Question

Very quick question :

I\'m trying to create a predicate builder like this :

    var predicate = PredicateBuilder.False();


        

Answer 1

Are you sure that the PredicateBuilder you were using was not a custom class? A PredicateBuilder is shipped as part of LINQKit but the source is also available here as follows:

public static class PredicateBuilder
{
    public static Expression<Func<T, bool>> True<T>() { return f => true; }

    public static Expression<Func<T, bool>> False<T>() { return f => false; }

    public static Expression<Func<T, bool>> Or<T> (this Expression<Func<T, bool>> expr1,
                                                      Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
        return Expression.Lambda<Func<T, bool>>
          (Expression.OrElse (expr1.Body, invokedExpr), expr1.Parameters);
    }

    public static Expression<Func<T, bool>> And<T> (this Expression<Func<T, bool>> expr1,
                                                       Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
        return Expression.Lambda<Func<T, bool>>
          (Expression.AndAlso (expr1.Body, invokedExpr), expr1.Parameters);
    }
}

Answer 2

Here is also a solution, it can parse a string expression to lambda expression like this

Expression<Func<Entity, bool>> predicate 
    = Interpreter.ParsePredicate<Entity>("id = 1 and name='Test'").Result;

Refer to https://github.com/linhnle/Kkts.Expressions