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copied!<p>I 've had the same problem with EF. Here's what I ended up doing:</p> <ol> <li>Instead of doing <code>story1.Tags.Add(new Tag { Name = ".net", })</code> yourself, routed all <code>Tag</code> creation through a helper method like this: <code>story1.Tags.Add(GetTag(".net"))</code>.</li> <li>The <code>GetTag</code> method checks the tags in the context to see if it should return an existing entity, like you do. If it does, it returns that.</li> <li>If there is no existing entity, it checks the <code>ObjectStateManager</code> to see if there are <code>Tag</code> entities added to the context but not already written to the db. If it finds a matching <code>Tag</code>, it returns that.</li> <li>If it still has not found the <code>Tag</code>, it creates a new <code>Tag</code>, adds it to the context, and then returns it.</li> </ol> <p>In essence this will make sure that no more than one instance of any <code>Tag</code> (be it already existing or just created) will be used throughout your program.</p> <p>Some example code lifted from my project (uses <code>InventoryItem</code> instead of <code>Tag</code>, but you get the idea).</p> <p>The check in step 3 is done like this:</p> <pre><code>// Second choice: maybe it's not in the database yet, but it's awaiting insertion? inventoryItem = context.ObjectStateManager.GetObjectStateEntries(EntityState.Added) .Where(ose => ose.EntitySet == context.InventoryItems.EntitySet) .Select(ose => ose.Entity) .Cast<InventoryItem>() .Where(equalityPredicate.Compile()) .SingleOrDefault(); if (inventoryItem != null) { return inventoryItem; } </code></pre> <p>If the <code>Tag</code> is not found in step 3, here's the code for step 4:</p> <pre><code>inventoryItem = new InventoryItem(); context.InventoryItems.AddObject(inventoryItem); return inventoryItem; </code></pre> <p><strong>Update:</strong></p> <p>It should be used like this:</p> <pre><code>Story story1 = new Story(); story1.Title = "Introducing the Entity Framework"; story1.Tags.Add(GetTag(".net", category, db)); story1.Tags.Add(GetTag("database", category, db)); </code></pre>

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