Entity Framework and DbContext - Object Tracking

Question

I am a bit confused on the usage of DbContext in Entity Framework. Here's the scenario I'm confused about.

• I use a linq query from the dbcontext to get data. Something like:

  List<Transactions> transactions = DefaultContext.Transactions.ToList();
  

• Then I update a column in one of the transactions returned in that query directly in the database.

• Then I call again:

  List<Transactions> transactions = DefaultContext.Transactions.ToList();
  

When the list returns back this time, it doesn't reflect the updates/changes I made when running the update statement, unless I loop through all my transactions and Reload them:

foreach (DbEntityEntry<Transactions> item in DefaultContext.ChangeTracker.Entries<Transactions>())
{
    DefaultContext.Entry<Transactions>(item.Entity).Reload();
}

Is this normal behavior? I assume that on my initial query, they are attached to the object context. Then when I query the second time, it doesn't make a trip to the database, and just pulls out the entities from the object context, unless I clear/detach or individually reload all of the entities.

Answer 1

It is normal and in case of DbContext API fixed behaviour because from some very strange reason neither DbSet or DbQuery expose MergeOption property. In case of ObjectContext API you can set the behaviour by MergeOption exposed on ObjectSet and ObjectQuery. So if you want to refresh values from database (and lose your changes) you can do:

ObjectContext objectContext = ((IObjectContextAdapter)dbContext).ObjectContext;
ObjectSet<Transactions> set = objectContext.CreateObjectSet<Transactions>();
set.MergeOption = MergeOption.OverwriteChanges;
List<Transactions> transactions = set.ToList();

If you just want to refresh transactions but you don't want to lose your changes you can use MergeOption.PreserveChanges instead.

Answer 2

That depends on the MergeOption of the DefaultContext.Transactions query. The default value, AppendOnly, won't overwrite objects already in your context. You can change this to OverwriteChanges to get the behavior you're expecting.