When Include() executing in Entity Framework?

Question

I have a simple question but didn't find an answers.
If I do so

var result = _db.Table.Include(t => t.Child).Where(t => t.Id == id).Single();

when join is calling? After it found my entity or it includes every child during SQL looking for the row?
Lets see at the example based on simple db model:

public class Head
{
    //... columns
    public virtual Child {get; set;}
    public Guid? ChildId {get; set;}
}
void main()
{
    //The first version of code
    var child = _db.Head.Include(h => h.Child)
        .FirstOrDefault(//boring staff but we don't need child here)
        ?.Child;
    if (child != null)
        foo(child);
    //The second one
    var head = _db.Head.FirstOrDefault(//boring staff);
    if (head != null && head.ChildId.HasValue)
        foo(head.Child); // I know here we make a new request to our db
}

Which of two options are more productive? I'm worry about "extra childs loading by SQL" when I need only one object based on filters query of parent table.
Thanks in advance!

Could you try to re-word your question? It's a little difficult to understand what the issue is — Mark C.
– Mark C., Commented Feb 2, 2017 at 15:12
I don't think you understand how Entity Framework works, this will only run a single query and will only do it when you call .Single(). You could easily have figured this out for yourself by profiling the database and watching the queries come in. You should learn to do that anyway. — DavidG
– DavidG, Commented Feb 2, 2017 at 15:15

Vijay · Accepted Answer · 2017-02-02 15:16:48Z

1

It will evaluate the where condition first. Not in C# but in SQL which gets generated. This will generate a SQL something like

SELECT top 1 .... FROM Table t
JOIN Child c ....
WHERE t.Id = id

Your database server will create a execution plan which will look for the item in the index and get corresponding child.

answered Feb 2, 2017 at 15:16

Vijay

5434 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user3818229 Over a year ago

I think this is what I tried to understand. I've updated my question by the way.

Sergey Kalinichenko · Accepted Answer · 2017-02-02 15:16:56Z

Without Include the loading of Child objects is deferred until you need them. Hence, if you were to iterate parent/child groups like this

foreach (var parent in _db.Table.Include(t => t.Child).Where(p => p.Name.StartsWith("Q")))
    foreach (var child in parent.Child)
        Console.WriteLine($"{child}, child of {parent}");

the number of round-trips would be equal to the number of parents plus one.

If you use Include, all Child objects are loaded along with the parent object, without making a separate round-trip for each parent. Hence, the number of database round-trips for the above code would be equal to 1.

In a case with Single, which could be rewritten as follows

var result = _db.Table.Include(t => t.Child).Single(t => t.Id == id);

the number of round-trips would be 1 with Include and 2 without Include.

Collectives™ on Stack Overflow

When Include() executing in Entity Framework?

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related