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Update with Adding a Relation

The Deep Save API can be used to update an existing object and set a relation with a new child (or parent). Consider the examples below:

Existing Parent and New Child

This example retrieves an existing parent object (Order) and uses the Deep Save API to perform the following:

  1. Save new child object (OrderItem)
  2. Establish relationship between the Order and the new OrderItem.

The Order object already has two related OrderItem objects before the sample code below runs:

order-with-relations

Important

When working with relationships, the Deep Save API applies the "accumulation" policy. This means the following: if a parent object in the database already has some related objects and you update the object with new child objects in the relation, these objects will be added to the relation.

The example uses blocking API for code brevity. When using in an Android application, keep in mind the blocking API cannot be used on the mail UI thread. Either run it in a separate thread or use the non-blocking API.

// get the order with the relations.
Map<String, Object> order = Backendless.Data.of( "Order" ).findFirst();

// create new order item
Map grapes = new HashMap();
grapes.put( "name", "Grapes" );
grapes.put( "price", 3.99 );

List<Map> orderItems = new ArrayList<>();
// add grapes to the existing order items on the server
orderItems.add( grapes );

// put the list with grapes added to it back into order
order.put( "orderItems", orderItems );

// deep save the order
Backendless.Data.of( "Order" ).deepSave( order );

// get the order object.
Order order = Backendless.Data.of( Order.class ).findFirst();

// create new order item
OrderItem grapes = new OrderItem();
grapes.name = "Grapes";
grapes.price = 3.99;

// add new order item to the existing ones
order.addItem( grapes );

// deep save the order
Backendless.Data.of( Order.class ).deepSave( order );
Order class. Public fields are used for brevity - JavaBean get/set methods are supported and recommended.
import java.util.ArrayList;

public class Order
{
  public String objectId;
  public Customer customer;
  public ArrayList<OrderItem> orderItems;

  public void addItem( OrderItem item )
  {
    if( orderItems == null )
      orderItems = new ArrayList<>();

    orderItems.add( item );
  }
}
OrderItem class. Public fields are used for brevity - JavaBean get/set methods are supported and recommended.
public class OrderItem
{
  public String name;
  public double price;
}

After the code runs, the new OrderItem object is saved in the database and the Order object relation is expanded to include it:

order-with-relations-after-deepsave