Question

I have following situation. I have Customer and CompanyCustomerAssignment objects (with 1:1 relation). One of properties in CompanyCustomerAssignment is CustomerGroup.
Now – I would like to QueryOver – when CustomerGroup is passed, than fetch Customers which belongs to this group, but when it comes as null I would like to query all. Well it seems simple in “SQL”:

...WHERE CustomerGroupId = @param OR @param is NULL;

Unfortunately I have no idea with QueryOver (custGrp is paramater – can be an object or null)

Customer c = null;
CompanyCustomerAssignment cca = null;

_session.QueryOver<Customer>(() => c)
    .JoinAlias(() => c.CompanyCustomerAssignment, () => cca)
    .Where(() => cca.Company == currentCompany && c.IsActive == true)
    .And(() => cca.CustomerGroup == custGrp || custGrp == null ) // <- this seems to be problem to me
    .List()
    .Select(x => new CustomerApiModel() {CustomerId = x.Id})
    .ToList();

But this does not work – I receive a message, that Customer does not have such a property, which sounds logical but does not help me at all.

Answer 1

In this case, we know the condition @param is NULL before the query is executed, or better before is assembled at all. So let’s extend Criteria with custGrp only if it is filled.

var criteria = _session.QueryOver<Customer>(() => c)
    .JoinAlias(() => c.CompanyCustomerAssignment, () => cca)
    .Where(() => cca.Company == currentCompany && c.IsActive == true);

// if during the query build
if(custGrp != null)
{
  criteria.Where(() => cca.CustomerGroup == custGrp);
}

var results = criteria
    .List()
    ... 

This makes the SQL part more efficient, and we can do more tricks…