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## 18.5.8.7 Working with Parent and Child Data in Regions

Learn about working with parent and child data in regions.

A BOSS business object can be related to one or more collections of composed child objects. For example, an `Order` object can compose a related collection of `OrderLine` child business objects. A parent object, like `Order`, can have multiple composed child collections, and each collection can comprise business objects that, in turn, contain composed collections. For example, each `OrderLine` business object that is part of an `Order` can have a composed collection of `OrderLineFulfillment` child business objects.

When working with a root business object like `Order` that has a composed child collection, clients like APEX can read and write child objects using a nested resource name that includes the resource key of a specific parent object. For example, to list the `OrderLine` child objects for order 12345, the REST endpoint would end with the path:

`/orders/12345/orderLines`

In the previous example, `12345` is the resource key of a specific order, and `orderLines` is the name of the Order object’s accessor attribute of type `object-collection`.

To work with the child objects of a specific `OrderLine` with resource key 67890, on a specific `Order` with resource key 12345, the REST endpoint URL would end with:

`/orders/12345/orderLines/67890/orderLineFulfillments`

The `orderLineFulfillments` is the name of the `OrderLine` object’s accessor attribute of type `object-collection`.

You can define REST Data Sources for the nested resources, using a named parameter in the URL path like this for the order lines:

`/orders/:orderId/orderLines`

To access a second-level child, the REST Data Source’s endpoint URL can contain multiple URL path parameters, for example:

`/orders/:orderId/orderLines/:orderLineId/orderLineFulfillments`

When using these parameterized REST Data Sources in a region on a page, you can then bind the value of the REST Data Source’s URL path parameters under the Parameters node in the Rendering tab for the region to use an appropriate page item.

Parent topic: Working with Oracle Cloud Applications BOSS REST Services