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Creating an Association Between Entities

You can define relationships between entities in your Business Data Connectivity (BDC) model by creating associations. Visual Studio generates methods that provide consumers of the model with information about each association. These methods can be consumed by SharePoint web parts, lists, or custom applications to display data relationships in a user interface (UI).

Create an association by choosing the Association control in the Visual Studio Toolbox, choosing the first entity (called the source entity), and then choosing the second entity (called the destination entity). You can define the details of the association in the Association Editor. For more information, see How to: Create an Association between Entities.

Applications such as SharePoint business data web parts consume associations by calling methods in the service class of an entity. You can add methods to the service class of an entity by selecting them in the Association Editor.

By default, the Association Editor adds an Association Navigation method to the source and destination entities. An Association Navigation method in the source entity enables consumers to retrieve a list of destination entities. An Association Navigation method in the destination entity enables consumers to retrieve the source entity that relates to a destination entity.

You must add the code to each of these methods to return the appropriate information. You can also add other types of methods to support more advanced scenarios. For more information about each of these methods, see Supported Operations.

You can create two types of associations in the BDC designer: foreign key-based associations and foreign keyless associations.

You can create a foreign key-based association by relating an identifier in the source entity to type descriptors defined in the destination entity. This relationship enables consumers of the model to provide an enhanced UI for their users. For example, a form in Outlook that enables a user to create a sales order that can display customers in a drop-down list; or a list of sales orders in SharePoint that enables users to open a profile page for a customer.

To create a foreign key-based association, relate identifiers and type descriptors that share the same name and type. For example, you might create a foreign key-based association between a Contact entity and a SalesOrder entity. The SalesOrder entity returns a ContactID type descriptor as part of the return parameter of Finder or Specific Finder methods. Both type descriptors appear in the Association Editor. To create a foreign key-based relationship between the Contact entity and SalesOrder entity, choose the ContactID identifier next to each of these fields.

Add code to the Association Navigator method of the source entity that returns a collection of destination entities. The following example returns the sales orders for a contact.

public static IEnumerable<SalesOrderHeader> ContactToSalesOrder(int contactID)
{
    const string ServerName = "MySQLServerName";
    AdventureWorksDataContext dataContext = new AdventureWorksDataContext
          ("Data Source=" + ServerName + ";" +
           "Initial Catalog=AdventureWorks;Integrated Security=True");

    IEnumerable<SalesOrderHeader> orderList = 
        from orders in dataContext.SalesOrderHeaders
             where orders.ContactID == contactID
             select orders;
    return orderList;
}

Add code to the Association Navigator method of the destination entity that returns a source entity. The following example returns the contact that is related to the sales order.

public static IEnumerable<Contact> SalesOrderToContact(int salesOrderID)
{
    const string ServerName = "MySQLServerName";
    AdventureWorksDataContext dataContext = new AdventureWorksDataContext
          ("Data Source=" + ServerName + ";" +
           "Initial Catalog=AdventureWorks;Integrated Security=True");

    int TempContactID = (from orders in dataContext.SalesOrderHeaders
                     where orders.SalesOrderID == salesOrderID
                     select orders.ContactID).Single();

    IEnumerable<Contact> contactList = from contacts in dataContext.Contacts
                                     where contacts.ContactID == TempContactID
                                     select contacts;
    return contactList;

}

You can create an association without mapping identifiers to field type descriptors. Create this kind of association when the source entity does not have a direct relationship with the destination entity. For example, a SalesOrderDetail table does not have a foreign key that maps to a primary key in a Contact table.

If you want to display information in the SalesOrderDetail table that relates to a Contact, you can create a foreign keyless association between the Contact entity and SalesOrderDetail entity.

In the Association Navigation method of the Contact entity, return the SalesOrderDetail entities by joining tables, or by calling a stored procedure.

The following example returns details of all sales orders by joining tables.

public static IEnumerable<SalesOrderDetail> ContactToSalesOrderDetail(int contactID)
{
    const string ServerName = "MySQLServerName";
    AdventureWorksDataContext dataContext = new AdventureWorksDataContext
          ("Data Source=" + ServerName + ";" +
           "Initial Catalog=AdventureWorks;Integrated Security=True");

    IEnumerable<SalesOrderDetail> orderList =
        from orders in dataContext.SalesOrderHeaders
        join orderDetails in dataContext.SalesOrderDetails on
            orders.SalesOrderID equals orderDetails.SalesOrderID
        where orders.ContactID == contactID
        select orderDetails;
    return orderList;
}

In the Association Navigation method of the SalesOrderDetail entity, return the related Contact. The following example demonstrates this.

public static IEnumerable<Contact> SalesOrderDetailToContact(int salesOrderID, int salesOrderDetailID)
{
    const string ServerName = "MySQLServerName";
    AdventureWorksDataContext dataContext = new AdventureWorksDataContext
          ("Data Source=" + ServerName + ";" +
           "Initial Catalog=AdventureWorks;Integrated Security=True");

    int TempContactID = (from orders in dataContext.SalesOrderHeaders
                         where orders.SalesOrderID == salesOrderID
                         select orders.ContactID).Single();

    IEnumerable<Contact> contactList = from contacts in dataContext.Contacts
                                       where contacts.ContactID == TempContactID
                                       select contacts;
    return contactList;
}
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