AddAssociation

AddAssociation allows you to add a one-to-many association between two entities. This method results in a foreign key constraint being added to the column that holds the primary key of the foreign table.

AddAssociation accepts a single parameter, associationPropertyName, which is the name of the entity member that holds the foreign key of another table.

To illustrate, if we were to add a new association between the TwitterUser and the TimelineItem classes that matches the existing association, we would first set about by adding a new property to the TimelineItem class to hold the id of a TwitterUser, like so:

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[Table]
public class TimelineItem : NotifyPropertyChangeBase
{
    string twitterUser2Id;

    [Column]
    public string TwitterUser2Id
    {
        get
        {
            return twitterUser2Id;
        }
        set
        {
            Assign(ref twitterUser2Id, value);
        }
    }

    EntityRef<TwitterUser> user2;

    [Association(Storage = "user2", ThisKey = "TwitterUser2Id",
                 IsForeignKey = true, Name = "FK_TwitterUser2")]
    public TwitterUser TwitterUser2
    {
        get
        {
            return user2.Entity;
        }
        set
        {
            user2.Entity = value;
        }
    }
...
}

On the other side, the one side of the association, we would create a new EntitySet property for the new TimelineItem children, as shown:

Click here to view code image

[Table]
[Index(Columns = "ScreenName")]
public class TwitterUser : NotifyPropertyChangeBase
{
    readonly EntitySet<TimelineItem> timelineItems2;

    [Association(
        Storage = "timelineItems2",
        OtherKey = "TwitterUserId")]
    public EntitySet<TimelineItem> TimelineItems2
    {
        get
        {
            return timelineItems2;
        }
        set
        {
            timelineItems2.Assign(value);
        }
    }
...
}

To materialize the association in the database, we would then perform the following updates:

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using (TwitterDataContext dataContext
                   = twitterDatabaseUtility.CreateContext())
{
    DatabaseSchemaUpdater updater
                   = dataContext.CreateDatabaseSchemaUpdater();
    updater.AddColumn<TimelineItem>("TwitterUser2Id");
    updater.AddAssociation<TimelineItem>("TwitterUser2");
    updater.Execute();
}