CODEWITHSUNDEEP
c#visual-studio-2010entity-framework.net-4.0entity-framework-4.1
mservidio
mservidio

Reputation: 13057

Entity Framework and DbContext - Object Tracking

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

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.

Upvotes: 2

Views: 7760

Answers (3)

Greg
Greg

Reputation: 2600

Related to the above, this is where I landed when I had this same error. But I wanted in my case to set Merge Option to No Tracking. I ran into this when I had an excel export method that was attempting to turn off object tracking of an IQueryable. Moving through lots of data that I wasn't going to be changing, I didn't need any change tracking.

A line of code similar to the below would fail on attempting to cast some IQueryables to class ObjectQuery (but succeed on others.)

var y = ((ObjectQuery)query).MergeOption = MergeOption.NoTracking;

Instead, I replaced this with usage of AsNoTracking

query = query.AsNoTracking();

Relating back to the original question, this would be potentially like the below, Extention method on DBQuery added in System.Data.Entity

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

Semi-Related Article: https://msdn.microsoft.com/en-us/library/hh949853(v=vs.113).aspx

Upvotes: 1

Ladislav Mrnka
Ladislav Mrnka

Reputation: 364249

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.

Upvotes: 8

Craig Stuntz
Craig Stuntz

Reputation: 126547

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.

Upvotes: 2

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