创建从EF 4.0到SQL Server 2008 R2的单个查询，而不是多个查询

Question

In following code, multiple queries will be run against the database for inserting one row at a time.

EF cause Multiple Database Trips: When I call c.SaveChanges, then EF 4.0 will run multiple UPDATE statements against the database, but will execute only one UPDATE per database trip. This means if we have 1000 UPDATE statements generated by EF 4.0, then we will end up making 1000 database trips, which is NOT a GOOD and OPTIMAL data approach in my view.

Is there any way of making EF 4.0 run a single batched query for all records updates in a single database trip? May be, if I could get the UPDATE query ( I mean the SQL query) for each record update, then I could just put all these queries into a single batched query and send the batched query to database, but I don't know if the UPDATE query for each record can be obtained in EF 4.0.

 public void SaveVendorOrders(int vendorId, int parentVendorId, string tag,
                              string desc, int productSegment, int productCategory)     
 {  
  using (Vendor c = new Vendor())
        {
            var query = (from p in c.Orders
                         where (p.VendorID == vendorId ||
                                p.ParentVendorID == parentVendorId)
                         select p);

            if (query.ToList().Count() > 0)
            {
                for (int i = 0; i <= query.ToList().Count() - 1; i++)
                {
                    query.ToList()[i].OrderTag = tag;
                    query.ToList()[i].OrderDescription = desc;
                    query.ToList()[i].ProductSegment = productSegment;
                    query.ToList()[i].ProductSegmentCategory = productCategory;
                }

                c.SaveChanges();
            }
        }
 }

EDIT 1:

As pointed out by SJuan76 and Hamlet Hakobyan, calling ToList repeatedly will execute a query repeatedly. But even that is solved by cleaning the code so ToList is called only once, my question remains: How to combine multiple updates into a single batched update query?

Answer 1

The query intended to deferred execution. It really executes whey you enumerate your query or, for instance, call ToList() . To avoid multiple enumerations you must call ToList() one time the your in-memory data in you method.

using (Vendor c = new Vendor())
{
  var query = (from p in c.Orders
               where (p.VendorID == vendorId ||
                      p.ParentVendorID == parentVendorId)
               select p).ToList();

  if (query.Count() > 0)
  {
      for (int i = 0; i <= query.Count() - 1; i++)
      {
          query[i].OrderTag = tag;
          query[i].OrderDescription = desc;
          query[i].ProductSegment = productSegment;
          query[i].ProductSegmentCategory = productCategory;
      }

      c.SaveChanges();
  }
}