Databases
StackOverflow2013
Postsdbo
POHow should I listen for entities being added/deleted from an ObjectContext?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POHow should I listen for entities being added/deleted from an ObjectContext?
    primarykey
    data
    text
    <p>As far as I can tell, <a href="http://msdn.microsoft.com/en-us/library/system.data.objects.objectcontext.aspx" rel="nofollow noreferrer"><code>ObjectContext</code></a> doesn't expose any direct way of listening for items being added/removed. You <em>could</em> hook up to the <a href="http://msdn.microsoft.com/en-us/library/system.data.objects.objectcontext.savingchanges.aspx" rel="nofollow noreferrer"><code>SavingChanges</code></a> event, and query the <a href="http://msdn.microsoft.com/en-us/library/system.data.objects.objectcontext.objectstatemanager.aspx" rel="nofollow noreferrer"><code>ObjectStateManager</code></a> for which items have been added or removed. But this has several problems:</p> <ul> <li>The notification will occur before the items are actually added to the context.</li> <li>The notification will occur any time <em>any</em> changes are saved (even if no items are added/removed).</li> <li>It doesn't appear to be how <a href="http://msdn.microsoft.com/en-us/library/system.data.objects.objectcontext.savingchanges.aspx" rel="nofollow noreferrer"><code>SavingChanges</code></a> was intended to be used--it is more for validating data than notifying of changes.</li> <li>This is subjective, but it just <em>feels</em> wrong to me.</li> </ul> <p>I've worked around this by implementing a limited version of the Repository Pattern--it handles creates, reads, and deletions, but updates are still performed by directly manipulating the properties of the entities themselves (and then saving changes from my repository).</p> <p>I'm slightly uneasy about this for a few reasons:</p> <ul> <li>I thought <a href="http://msdn.microsoft.com/en-us/library/system.data.objects.objectcontext.aspx" rel="nofollow noreferrer"><code>ObjectContext</code></a> was supposed to replace the repository from the repository pattern. It feels like I am duplicating work that the Entity Framework should be doing for me.</li> <li>Using an incomplete version of the Repository Pattern (the C, R, and D from CRUD) seems a little strange. Shouldn't a repository either be used for all 4 CRUD operations, or none?</li> <li>There must be a reason that the Entity Framework doesn't support add/delete notifications. By choosing to implement them anyway, am I creating a design headache that the Entity Framework developers chose to avoid?</li> </ul> <p>For reference, here is a rough outline of my repository:</p> <pre><code>public class EntityArgs&lt;T&gt; : EventArgs where T : EntityObject { .... public T Entity { get { return this.entity; } } } public delegate void EntityEventHandler&lt;T&gt;(object sender, EntityArgs&lt;T&gt; args) where T: EntityObject; public class EntityRepository { public event EntityEventHandler&lt;Foo&gt; FooAdded; public event EntityEventHandler&lt;Foo&gt; FooDeleted; ... public EntityRepository() { this.entities = new Entities(); } public IEnumerable&lt;Foo&gt; Foos { get { return this.entities.Foos; } } public void AddFoo(Foo foo) { this.entities.Foos.AddObject(foo); this.entities.SaveChanges(); this.OnFooAdded(foo); } public void DeleteFoo(Foo foo) { this.entities.Foos.DeleteObject(foo); this.entities.SaveChanges(); this.OnFooDeleted(foo); } public void SaveChanges() { this.entities.SaveChanges(); } ... } </code></pre> <p>I'm quite new to the Entity Framework, so let me know if my approach is totally wrong.</p> <p>EDIT: In response to Erix's suggestion to use <code>ObjectStateManager</code>, it <em>almost</em> addresses my issue, but not quite. The problem is that I want to be notified when <code>entities.Foos</code> will have the changes reflected in it. <code>ObjectStateManager.ObjectStateManagerChanged</code> occurs when <code>AddObject</code> is called, but before <code>SaveChanges</code> is called. So:</p> <pre><code>entities.ObjectStateManager.ObjectStateManagerChanged += (s, e) =&gt; Console.WriteLine("Action: {0}, Object: {1}, Count: {2}", e.Action, e.Element, entities.Foos.Count()); var foo = ... Console.WriteLine("Count: {0}", entities.Foos.Count()); entities.Foos.AddObject(foo); entities.Foos.SaveChanged(); Console.WriteLine("Count: {0}", entities.Foos.Count()); // Output: // Count: 0 // Action: Add, Object: ..., Count: 0 // Count: 1 </code></pre>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USmarc_s
    1. USMatthew
    plurals
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POHow should I listen for entities being added/deleted from an ObjectContext?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POHow should I listen for entities being added/deleted from an ObjectContext?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COWhat events are you interested in and why? A object being added/removed from the context, or a record being inserted or deleted from the database?
      singulars
      1. POHow should I listen for entities being added/deleted from an ObjectContext?
      1. USPaul Turner
    2. CO@ProgrammingHero: An object being added/removed from the context.
      singulars
      1. POHow should I listen for entities being added/deleted from an ObjectContext?
      1. USMatthew
    3. CO@ProgrammingHero: As for why, I am interested for a variety of reasons. One simple example would be so that I can know when to update a displayed list of entities meeting some criteria.
      singulars
      1. POHow should I listen for entities being added/deleted from an ObjectContext?
      1. USMatthew
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload