Question

I am new to lambda expressions and I am having issues trying to figure out how to represent my entity framework query in one. I also could be wrong and there is just a better way to do what I want. If this is true please let me know. My scenario is I have an advanced search screen where you could choose to search bu name, customer number, or phone number. You can search by more than 1 if you want. I am using Entity Framework as my backend and have repositories set up for my tables. Below is the code I am trying to use

Func<Parties, bool> exp;

exp = null;

if (vm.CustomerNumberCriteria != null)
{
    custID = Convert.ToInt32(vm.CustomerNumberCriteria);
    exp = o => o.ID == custID;
}


if (vm.NameCriteria != null)

    exp += o => o.LastName.Contains(vm.NameCriteria) || o.FirstName.Contains(vm.NameCriteria) || o.MiddleName.Contains(vm.NameCriteria) || o.Designation.Contains(vm.NameCriteria);

if (vm.PhoneNumberCriteria != null)

    exp += o => o.CentralPhoneNumbers.Any(child => child.PhoneNumber == vm.PhoneNumberCriteria);

//TODO set tempresults
tempresults = custs.All.Where(exp).ToList();

My issue is it seems to treat this like an and and I need results if there is a match on any of the search criteria.

Thanks

Answer 1

There are two big problems here. Firstly, you’re using delegates, not expression trees – which means your entire table is going to be pulled back to the client and filtered there. You want Expression<Func<Parties, bool>>.

Now, if you want to build up “or” expression trees, the simplest approach is to use PredicateBuilder:

var predicate = PredicateBuilder.False<Parties>();

if (vm.CustomerNumberCriteria != null)
{
    custID = Convert.ToInt32(vm.CustomerNumberCriteria);
    predicate = predicate.Or(o => o.ID == custID);
}

if (vm.NameCriteria != null)
{
    custID = Convert.ToInt32(vm.CustomerNumberCriteria);
    predicate = predicate.Or(o => o.LastName.Contains(vm.NameCriteria) /* etc */)
}

if (vm.PhoneNumberCriteria != null)
{
    predicate = predicate.Or(o => o.CentralPhoneNumbers.Any
                     (child => child.PhoneNumber == vm.PhoneNumberCriteria));
}

tempresults = custs.All.Where(predicate).ToList();