All data access to and from a client application occurs through REpresentational State Transfer (REST) calls.
The Visual Builder user interface provides access to two basic kinds of data:
- Business objects in Visual Builder, which you can create yourself and use in applications
- Service connections, which can be Oracle services or external REST services
When you create a business object, a REST API is automatically created for you, with GET, POST, PATCH, and DELETE endpoints.
When you create a service connection, you can obtain REST APIs in one of the following ways:
- Select objects from a service catalog
- Provide a service specification document in OpenAPI/Swagger or Oracle Application Developer Framework (ADF) Describe format
- Specify an endpoint URL, an HTTP method, and an action hint
Each of these mechanisms generates REST APIs for you to use. You can specify request and response payload structures in JSON format, and you can provide a subset of query parameters to expose to the Visual Builder user interface. Parameters can have a type (but are assumed to be primitives). You can also use the provided REST helper utility to call REST endpoints.
For full details on using REST for data access in Visual Builder, see Introduction to Accessing Business Objects in Accessing Business Objects Using REST APIs.
You can create variables and action chains to call REST endpoints from your applications, retrieving and sending data to and from the endpoints. Typically, the type of the variable matches the structure of the REST payload. You have the option of defining your own type that more closely matches your use case, and then mapping from the REST payload to a variable instance that uses that type. For example, for advanced cases, you could define a variable type that matches your own page design, and then map one or more REST payloads to that type. To send that data back to a service or services, you would again map the data of that variable to the REST payloads.
Components are bound to variables. These variables do not have any intrinsic knowledge of where their data is derived from or what their data is used for. To populate a variable from a REST call, you assemble an action chain from an action making that REST call and an action assigning the result to that variable. In the common case, the Visual Builder user interface automates the creation of that variable to match the payload of the REST call, enabling you to quickly bind the REST call's payload in your application pages. To handle a POST or DELETE action, you compose an action chain with the REST action, passing in the variable as the payload.
Mapping to and from REST
In more advanced cases, you may wish to define a model (through the use of a variable) that more closely matches your specific application. In other cases, the GET and POST (or equivalent methods) may be asymmetrical or may be from different services entirely. In these cases, you can map the REST payload to and from that variable.