Handling REST Requests
At runtime, Mobile SDK creates a singleton instance of RestClient. You use this instance to obtain a RestRequest object and to send that object to the Salesforce server.
Although you can use RestRequest objects for many CRUD operations, let’s look at the most common use case: SOQL queries. Most other types of requests use the same flow with different input values. By default, SOQL query requests return up to 2,000 records per batch. In Mobile SDK 9.1 and later, you can specify a batchSize argument to customize the maximum batch size. This argument accepts any integer value between 200 and 2,000. Specifying a batch size does not guarantee that the returned batch is the requested size.
To create and send a SOQL REST request to the Salesforce server, follow these steps:
RestClient takes a SOQL query. It creates a request object.
For example, using the following request:
Pass the request to the RestClient.shared.publisher. In case you’ve never encountered call chaining, the following code comments describe what happens in a typical publisher sequence. This code is from the fetchContactsForAccount method of the Swift template app’s ContactsForAccountModel class.
Contact and ContactResponse are structs that represent, respectively, a Contact record, and the formatted REST response to the SOQL query. Both objects are declared “Decodable”.
Do you see the beauty of using the RestClient publisher? You can send the request and handle the response in a single block of logic.
Typically, Swift apps handle the asynchronous response in the trailing closure, as shown here.
In the following alternate example, the calling object implements the RestClientDelegate protocol to handle responses. It therefore calls the send(request:delegate:) overload and passes itself as the delegate.
Pass the request object to the send: parameter of the send:delegate: method. Typically in Objective-C apps, the calling object handles the asynchronous response in its own implementation of the SFRestDelegate protocol, as shown here.