如何使用Entity Framework中另一个表上的外键引用的汇总值更新表的所有行

Question

I have a users table and my User entity has a Rating column. A User has a navigation property called IncomingRatings , which is a one-to-many relationship of list of Rate s from a table called rates. A rating can be positive or negative, and is represented by the IsPositive boolean.

I want to find all the ratings of that user, and store it in the Rating column of my User table. Consider the following sample data:

RaterID | RatedID | IsPositive
1         2         1
4         1         0
5         2         1
2         3         0
3         2         1
7         2         0
6         1         1  

In this case, for example, I want my user #2's (referenced by ID 2) Rating field to become 3, as there are 3 positive ratings for her.

After the updates, the users table should be like this:

UserID | Rating
1        1
2        3
3        0
4        0
5        0
6        0
7        0

Because I need this statement to run for 10000+ records, I can't use regular for loop in my ASP.NET website to update the records as it will save them one-by-one when I call SaveChanges . I've found EntityFramework.Extended which can update many records in a single call. Here is my two approaches:

db.Users.Where(u => true).Update(u => new User { Rating = u.IncomingRatings.Count(r => r.IsPositive) });
db.Users.Where(u => true).Update(u => new User { Rating = db.Rates.Where(r => r.RatedID == u.ID && r.IsPositive).Count() });

However, I am getting An aggregate may not appear in the set list of an UPDATE statement. error in both queries. How can I update all rows with an aggregate value in Entity Framework 6.1?

Answer 1

Looks like EntityFramework.Extended is only capable of building simple UPDATE statement like

UPDATE User SET Rating = 3 WHERE ...

and not (or not yet)

UPDATE User SET Rating = (SELECT Count(*) FROM ... )

Too bad...

If doing the updates by regular EF updates, but with one SaveChanges() call, is too slow you could consider executing raw SQL to do the job.