实体框架如何在多对多关系中插入唯一值而无需手动检查

Question

Does anyone know how to insert unique values without explicitly having to check for an existing value?

I am able to make this work, but I am less than impressed with the code I had to write. Basically I created a helper function to check a unique value on my container.

The structure is pretty basic.

[ Entry ] *<----->* [ UniqueValue ]

Main code

public static void ImportStuff ()
{
    //Generate a list of importable items
    List<DtoItems> items = DtoItemGetter.GetItems();
    using( var container = new MyEntities() )
    {
        foreach( var item in items )
        {
            Entry newEntry = CreateNewEntry( item );

            //******** 
            // Here's the call to my helper method to check 
            // for the uniqueness of the values on the item I am importing
            //******** 
            item.UniqueValuesList.ForEach( 
                uv => HelperMethod( container, newEntry, uv ) );

            containter.AddToEntries( newEntry );

            //Less important... but it would be nice if I didn't 
            // have to save everytime I add an new entry... but 
            // this necessary for the Helper check.
            container.SaveChanges();
        }
    }
}

Helper Method

public static void HelperMethod( 
    MyEntities container, Entry newEntry, string checkValue )
{
    UniqueItem unique = null;

    //Have to check to see if it already exists in the DB
    container.uniqueItems.ForEach( uv => { 
        if( uv.Name == checkValue )
        {
            unique = uv;
        } } );

    //Here's the money, either add the one I found, or 
    //create a new one... meh
    newEntry.UniqueItems.Add( 
        unique ?? new UniqueItem { Name = checkValue } );
}

Hopefully this makes enough sense.

Answer 1

Entity framework doesn't support unique constraints yet - http://blogs.msdn.com/b/efdesign/archive/2011/03/09/unique-constraints-in-the-entity-framework.aspx

So if you want to use unique constraints you should set the constraint on the database manually and check by hand.

EF Codefirst validate unique property?