实体框架非常慢

Question

I have thousands of contacts in just one group (contacts and groups have a many-to-many relationship) :

public class Group
{
    public int GroupID { get; set; }
    public string Name { get; set; }

    public virtual ICollection<Contact> Contacts { get; set; }
}

public class Contact
{
    public int ContactID { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public virtual ICollection<Group> Groups { get; set; }
}

When I fetch all the contacts, it takes half a second. No problem :

context.Contacts.ToList();

I tried this and it took again less than a second :

 db.Contacts.SelectMany(s => s.Groups.Where(c => c.GroupID == 1)).ToList();

However, this took 15 seconds to load (it hangs on the second line) :

var groups = context.Groups.Include(x => x.Contacts);
foreach(var group in groups)
{
     foreach(var contact in group.Contacts)
     {
         contactsInGroup.Add(contact);
     }
}

Same problem here (it hangs on the fourth line) :

var groups = context.Groups.ToList();
foreach(var group in groups)
{
     db.Entry(group).Collection(p => p.Contacts).Load(); 

     foreach(var contact in group.Contacts)
     {
         contactsInGroup.Add(contact);
     }
}

Anybody understand why ?

Answer 1

Include() and Load() both to load related entities EagerLoading or LazyLoading respectively.

I think you can improve your performance to add index in your model

public class Group
{
 [Index("GroupIdIndex", 1)]
 public int GroupID { get; set; }
 public string Name { get; set; }

 public virtual ICollection<Contact> Contacts { get; set; }
}

public class Contact
{
 [Index("ContactIdIndex", 1)]
 public int ContactID { get; set; }
 public string FirstName { get; set; }
 public string LastName { get; set; }

 public virtual ICollection<Group> Groups { get; set; }
}