Saving to a Entity that has Many To Many relationship

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);
}