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Request handling ​

TWiRLClientResource ​

Once TWiRLClient and TWiRLClientApplication have been initialized, it is possible to make the ReST calls. Also in this case it is possible to use the fluent syntax and, since the implementation is done through interfaces, it is not necessary to destroy the WiRL objects.

pascal
function TMainDataModule.GetPerson(Id: Integer): TPerson;
begin
  Result := WiRLClientApplication1
    // Create the invokation object for the resource
    .Resource('person')
    // Set the accept header (necessary for the server
    // to decide the format of the response)
    .Accept('application/json')
    // Set the *Id* parameter
    .QueryParam('Id', Id.ToString)
    // Make the call deserializing the response
    // into an object of type TPerson
    .Get<TPerson>;
end;

With this example, WiRLClientApplication1 is asked to generate a new TWiRLInvocation on the indicated resource. Through the Accept and QueryParam methods, the headers and parameters required by the server are set. The Get method will start the actual request and the body of the message returned by the server will be used to create an object of type TPerson as indicated.

User-created objects ​

Another way of use TWiRLInvocation is to give to the Get method (the same thing also applies to Post, Put, Delete, etc.) an object created by us that will be "filled" with the data provided by the server.

pascal
function TMainDataModule.GetPersonName(Id: Integer): string;
var
  LPerson: TPerson;
begin
  LPerson := TPerson.Create;
  try
    WiRLClientApplication1
      .Resource('person')
      .Accept('application/json')
      .QueryParam('Id', Id.ToString)
      .Get(LPerson);
    Result := LPerson.Name;
  finally
    LPerson.Free;
  end;
end;

This approach is very useful when the server returns an array of objects. For examples if the properties of the objects are equivalent to the fields of a dataset, WiRL is able to populate the fields of the DataSet (for example a memory table) automatically.

pascal
procedure TMainDataModule.GetPeople(ADataSet: TDataSet);
begin
  WiRLClientApplication1
    .Resource('person')
    .Accept('application/json')
    .Get(ADataSet);
end;

Read the response at a low level ​

In some cases it may be useful to read the server response in more detail. For example, the server could return different JSONs depending on certain headers or the status code. In this case we need to access IWiRLResponse which contains all the information of the response.

pascal
function TMainDataModule.GetPerson(Id: Integer): TPerson;
var
  LResponse: IWiRLResponse;
begin
  LResponse := WiRLClientApplication1
    .Resource('person')
    .Accept('application/json')
    .QueryParam('Id', Id.ToString)
    .Get<IWiRLResponse>;
  // Do something with the response
  if LResponse.Headers.ContentType <> 'application/json' then
    Abort;
  Result := LResponse.Content.AsType<TPerson>();
end;

More ​

There are many other useful features of WiRL Client such as:

  • Filter management
  • Authentication and authorization
  • Customization of message body readers and writers
  • Creation of new "vendors" for TWiRLClient
  • Asynchronous calls