Lambda expression to create AND filter

Question

I used this code to create a search filter.

I need is to pass an array of data and filter this data by AND.

Expression<Func<serveis, bool>> CombineWithAnd<T>(Expression<Func<T, bool>> firstExpression, Expression<Func<T, bool>> secondExpression)
{            
    var parameter = Expression.Parameter(typeof(T), "z");            
    var resultBody = Expression.AndAlso(Expression.Invoke(firstExpression, parameter), Expression.Invoke(secondExpression, parameter));

    return Expression.Lambda<Func<serveis, bool>>(resultBody, parameter);    
}

And then:

Expression<Func<T, bool>> resultExpression = n => false;     

foreach (var car in cars)
{    
    Expression<Func<T, bool>> expression = x => x.color_car.Any(z => z.car == car);
    resultExpression = CombineWithAnd(resultExpression, expression);
}

query = query.Where(resultExpression.Compile());

If I use this same code using OR or OrElse the search works correctly.

But I also need to perform the search by AND or AndAlso and it always returns zero results.

And I've checked in the database and there are both AND and OR results.

score 4 · Accepted Answer · answered Nov 06 '17 at 15:51

For AND, you should replace the starting "left side":

Expression<Func<T, bool>> resultExpression = n => false;

with:

Expression<Func<T, bool>> resultExpression = n => true;

because currently the left side fails your condition regardless of the right side

Lambda expression to create AND filter

1 Answers1