Batch Update using LINQ

Question

The following save all in once, How do I make a batch of 50 and save a batch instead of saving all in once.

dbUserList will have around 50k objects.

var dbUserList = db.Users.Where(x => users.Select(y => y.Id).Contains(x.Id));
foreach (var user in users)
{
     var dbUser = dbUserList.First(x => x.Id == user.Id);
     dbUser.name = user.name;
     dbUser.cat = user.cat;
}
db.SaveChanges();

Answer 1

foreach (var user in users)
{
     db.Users.Attach(user);
     db.Entry(user).State = System.Data.Entity.EntityState.Unchanged;
     db.Entry(user).Property(c=> c.name).IsModified=true;
     db.Entry(user).Property(c=> c.cat).IsModified=true;
}
db.SaveChanges();

i think this is what you wanted. update them all without query them all.

Answer 2

You need to use skip/take in LINQ to get around this. The code below should work. Although I'm not always a fan of doing a while(true) with a break statement, it's the easiest way to implement this.

int takeCount = 50;
int skipAmount = 0;

while (true)
{
    var dbUserList = db.Users.Where(x => users.Select(y => y.Id).Contains(x.Id)).OrderBy(x => x.Id).Skip(skipAmount).Take(takeAmount);
    if (!dbUserList.Any)
    {
        break;
    }

    foreach (var user in users)
    {
       var dbUser = dbUserList.First(x => x.Id == user.Id);
       dbUser.name = user.name;
       dbUser.cat = user.cat;
    }
    db.SaveChanges();
}