A request transformation (or transform) function is generally specified on the service endpoint. It can also be specified on the ServiceDataProvider variable, which overrides the endpoint one.

A request transform function is called right before a request is made to the server/endpoint. It provides a chance for page authors to transform the options (paginate, filter, sort, and so on) and build the final (request) configuration. The ServiceDataProvider supports a predefined list of request transform function types, described in this section. Note that there are no guarantees of the order in which transform functions are called, except that vbPrepare is called first and body transform is called last.

Each request transformation function has the following signature (except in the case of vbPrepare and fetchByKeys transform):

function (configuration, options, transformsContext) { 

    // process the options and update configuration object
    return configuration; 
} 

The parameters to the function are:

• configuration: An object that has the following properties:

  • endpointDefinition: The metadata pertaining to the endpoint.
  • fetchConfiguration: The configuration pertaining to this fetch call. If fetch was initiated by ServiceDataProvider, this includes the following properties:
    • capability: The fetch capability, like fetchByKeys, fetchFirst, fetchByOffset.
    • context: A snapshot of the ServiceDataProvider variable state at the time the fetch call was made.
    • externalContext: If the fetch was externalized to a chain, then the context setup on the RestAction in that chain.
    • fetchParameters: A snapshot of the original fetch parameters provided by the initiator of the fetch (such as a component). The parameters passed to the fetch call are defined by the JET Data Provider fetch API.
    • transformsOptions: The full set of transforms options that are passed to each transform function. These are computed using the parameters configured on the Service Data Provider, the RestAction (if applicable), and the input parameters provided by initiator (such as the component).

  • initConfig: Map of another configuration passed into the request. The 'initConfig' exactly matches the 'init' parameter of the request.

  • parameters: Path and query parameters. These are not writable.

  • url: Full URL of the request.

• options: An object that is relevant to the type of transformation function. For a filter function, for example, this would be the filterCriterion.

• transformsContext: A context object, set by the author (ServiceDataProvider, RestHelper, Call Rest action), that is then passed to every transform function to store or retrieve any contextual information for the current request lifecycle.

If transformations are needed for a specific data provider instance, these functions can be defined on the ServiceDataProvider variable under the 'transforms' property. For externalized fetch cases, the RestAction properties can be used for configuring transformations.