Question

I usually use a “Page -> Service -> Repository” pattern in my applications putting all my database calls in “repository” classes.

In some situations I’ve to test collection items count in my service logic.

Example:

EventService eventService=container.Resolve<EventService>();
IEnumerable<Event> events=eventService.GetAll();
if(events.Count()>0)
{
    ...do something...
}

Using NHibernate this will generate automatically a SQL statement with a DB access out of my repository class.

Can I avoid this? Is there a best practice?

Answer 1

I try to avoid exposing IQueryable<T> on repositories for the following reasons:

• Many of the methods or not supported and it is not always clear what kind of query will be generated.
• Supporting ad hoc queries undermines the importance of designing proper indexes for specific uses cases.
• You lose the specification of the kind of queries that are expected.

Instead I would opt for using a simple query object which is translated into whatever it needs to be by the repository.

For this case in particular I would have a method on the repository returning a paginated list of events:

IList<Event> GetAll(int startIndex, int count);

This also highlights the importance of pagination. In the repository this would like something like:

this.Session.Linq<Event>().Skip(startIndex).Take(count).ToList();

You may also choose to create a wrapping object for IList which can contain the total count as well.