Performance of Entity Framework Core

问题

I'm quite new to the EF Core. I always used the EF 6.0 and never had to use an include. Now the question comes up how i should work with these includes. I figured out three possible options and wanted to know wich would you prefer to use/which is the fastest and why?

In these samples my intention is to get the details of a club. I want to check if a club with the corresponding id exists and then get the whole information.

Option 1:

using (var context = new TrainingSchedulerContext())
{
    var clubs = context.Clubs.Where(c => c.Id == clubId);
    if (clubs.Count() == 0)
        return NotFound();

    var club = clubs.Include(c => c.Memberships)
        .Include(c => c.MembershipRequests)
        .Include(c => c.TrainingTimes)
        .Include(c => c.AdminRoles)
        .SingleOrDefault();
}

Option 2:

using (var context = new TrainingSchedulerContext())
{
    var club = context.Clubs.Include(c => c.Memberships)
            .Include(c => c.MembershipRequests)
            .Include(c => c.TrainingTimes)
            .Include(c => c.AdminRoles)
            .SingleOrDefault(c => c.Id == clubId);

    if (club == null)
        return NotFound();
}

Option 3:

using (var context = new TrainingSchedulerContext())
{
    var club = context.Clubs.SingleOrDefault(c => c.Id == clubId);
    if (club == null)
        return NotFound();

    club = context.Clubs.Include(c => c.Memberships)
        .Include(c => c.MembershipRequests)
        .Include(c => c.TrainingTimes)
        .Include(c => c.AdminRoles)
        .SingleOrDefault(c => c.Id == clubId);
}

回答1:

Let's go from worst to best:

Option 3: this is obviously the worst. You are downloading the entire item into memory just for throwing it away. This is a waste of resources.
Option 1: this is not the best way because you are executing 2 queries against the database, one for Count and another one for SingleOrDefault. The first one is not needed, hence:
Option 2: this is the best case because if the item does not exist, nothing will be downloaded from the database, so you don't have to worry about that, and it's also a single database call.

来源：https://stackoverflow.com/questions/49447231/performance-of-entity-framework-core

标签

linq

entity-framework-core