How to execute huge SQL queries rapidly with EFCore? - sql-server

Question

Here are two simplified examples of SQL queries I recently run on my SQL database:
insert into new_entity
select top 10000 field1,
field2
from old_entity
&
update top 1000 e
set field1 = 13
from entity e
where field1 is null
Their execution was so fast it's barely noticeable.
However, if I want to perform the same operation using EF, the way I know would be iterating over each object:
using(var db = new myDbContext())
{
var new_objs = db.old_entity.Take(10000).Select(ot=> new new_entity() { ... });
db.new_entity.AddRange(new_objs);
db.SaveChanges();
}
&
using(var db = new myDbContext())
{
var objs = db.entity.Where(e => e.field1 == null).Take(1000);
objs.ForEach(e => e.field1 = 13);
db.SaveChanges();
}
Which lasted for hours, which is unacceptable.
I can execute a raw SQL query from within the app, but for real-life complex objects, it's a dradgery.
Is there a way to code such operations using the EF model with a performance of a directly written query?

Answer 1

EF Core 7 have introduced new method ExecuteUpdate. And your query for update can be written in the following way:
using(var db = new myDbContext())
{
var objs = db.entity.Where(e => e.field1 == null).Take(1000);
objs.ExecuteUpdate(b => b.SetProperty(x => x.field1, x => 13));
}
INSERT FROM is not supported by EF Core any versions.
Anyway, you can install third-party extension linq2db.EntityFrameworkCore, note that i'm one of the creators.
Insert
using(var db = new myDbContext())
{
var new_objs = db.old_entity.Take(10000).Select(ot=> new new_entity() { ... });
new_objs.Insert(db.new_entity.ToLinqToDBTable());
}
Update
using(var db = new myDbContext())
{
var objs = db.entity.Where(e => e.field1 == null).Take(1000);
objs
.Set(x => x.field1, x => 13)
.Update();
}