Resetting the context and accessing a query from a previous one

Question

I am processing a very large amount of data. In an effort to speed up EF, I've found that calling SaveChanges() in chunks has helped. Also, I read that resetting the context every so often will speed things up as well. I am having trouble implementing this.

context = new Context();
List<object> results = context.someQuery.ToList();
// do stuff to results to get it ready for processing in the for loop

for (int i = 0; i < results.Count; i++)
{
    // do stuff like Add and Modify
    if (results[i] == target)
        context.myDataSet.DeleteObject(target);
    if (i % 10 == 0)
        context.SaveChanges();
    if (i % 100 == 0)
    {
        context.Dispose();
        context = new Context();
    }
} 

It seems like DeleteObject() is not working once the context is reset. What can I do to get something along these lines working? I really don't want to have to re query the db (i.e., move the query into the for loop and do it again every time I reset the context), since I do a lot of preprocessing to it and don't want to keep repeating this.

Answer 1

Try

using(var context = new Context())
{
    context.Entry(new Entity { Id = 5} ).State = Deleted;
    context.SaveChanges();
}

Answer 2

I think you can handle this using transactions (or Unit of Work pattern as a better solution):

context = new Context();
var transaction = context.Database.BeginTransaction();
List<object> results = context.someQuery.ToList();
// do stuff to results to get it ready for processing in the for loop

for (int i = 0; i < results.Count; i++)
{
    // do stuff like Add and Modify
    if (results[i] == target)
        context.myDataSet.DeleteObject(target);
    if (i % 10 == 0)
        context.SaveChanges();
    if (i % 100 == 0)
    {
        transaction.Commit();
        transaction.BeginTransaction();
    }
}

Do you have to rollback in case of an error in your queries? If so, please check out Unit of Work pattern