Saving to a Entity that has Many To Many relationship - c#-4.0

Question

I have a set of tables (ConditionTemplate and KeyWord) that have a many to many relationship. In code I am trying to add a Keyword to a specific ConditionTemplate record. Unfortunately, when I think I'm adding a Keyword to a specific condition I'm getting an error as if it's adding a new Keyword without being associated to a condition.
An Image of my Model:
My Code:
Global Variables Creation:
EnterpriseEntities EE;
ConditionTemplate myConditionTemplate;
Load Global Variables:
EE = new EnterpriseEntities();
EE.Database.Connection.ConnectionString = Myapp.EnterpriseEntityConnectionString;
myConditionTemplate = EE.ConditionTemplates.Where(c => c.TemplateCode == "17D").FirstOrDefault();
The above code loads a single Condition with Many Keywords.
Available Keywords are in a listbox and the user pushed a button to select a keyword(s) to move to the condition. This is the code that handles that.
foreach (KeyWord SelectedKeyWord in ListBoxAvailableKeyWords.SelectedItems)
{
KeyWord NewKeyWord = new KeyWord
{
KeyWordID = SelectedKeyWord.KeyWordID,
ID = SelectedKeyWord.ID,
Word = SelectedKeyWord.Word
};
myConditionTemplate.KeyWords.Add(NewKeyWord);
}
Then the user pushes a button to save changes and I call
EE.SaveChanges
Then I get this error:
System.Data.UpdateException: An error occurred while updating the
entries. See the inner exception for details. --->
System.Data.SqlClient.SqlException: Violation of UNIQUE KEY constraint
'IX_KeyWord'. Cannot insert duplicate key in object 'dbo.KeyWord'. The
duplicate key value is (ADJUDICATION). The statement has been
terminated.
If I remove the code that sets the word property (Word = SelectedKeyWord.Word
) when I create the keyword object I get this error.
System.Data.Entity.Validation.DbEntityValidationException: Validation
failed for one or more entities. See 'EntityValidationErrors' property for more details.
Which tells me the word field is required.

Answer 1

In order to tell EF that the KeyWords you selected already exist in the database and to avoid the problem you must attach them to the context:
foreach (KeyWord SelectedKeyWord in ListBoxAvailableKeyWords.SelectedItems)
{
KeyWord NewKeyWord = new KeyWord
{
// You actually only need to set the primary key property here
ID = SelectedKeyWord.ID
};
EE.KeyWords.Attach(NewKeyWord);
myConditionTemplate.KeyWords.Add(NewKeyWord);
}
Edit
If the KeyWord entities are already attached to your context (because they have been loaded before with the same context for example) you can use instead:
foreach (KeyWord SelectedKeyWord in ListBoxAvailableKeyWords.SelectedItems)
{
KeyWord NewKeyWord = EE.KeyWords.Find(SelectedKeyWord.ID);
myConditionTemplate.KeyWords.Add(NewKeyWord);
}