Devart Client (UniDAC, MyDAC, IBDAC)

When the server exposes datasets with a Devart integration (UniDAC, MyDAC, IBDAC), a Delphi client fetches them into TVirtualTables (Devart's in-memory dataset), shows and edits them with the usual data-aware controls, and can send them back. The components are the same for the three libraries, with their own names:

Library	Unit	Multi-dataset	Single dataset	Package
UniDAC	MARS.Client.UniDAC	TMARSUniDACResource	TMARSUniDACDataSetResource	MARSClient.UniDAC
MyDAC	MARS.Client.MyDAC	TMARSMyDACResource	TMARSMyDACDataSetResource	MARSClient.MyDAC
IBDAC	MARS.Client.IBDAC	TMARSIBDACResource	TMARSIBDACDataSetResource	MARSClient.IBDAC

They exchange datasets in the native format of the library (application/json-unidac, -mydac, -ibdac) and need the define of the library (MARS_UNIDAC, MARS_MYDAC, MARS_IBDAC). The MARSClient.<Library>Design packages register them on the MARS-Curiosity Client page of the palette; they work as well when created in code, which needs no design package (the demos do so).

Multi-dataset resource

ResourceDataSets pairs the name of each dataset of the response with a local TVirtualTable:

SummaryResource := TMARSMyDACResource.Create(Self);
SummaryResource.Application := MARSApplication;
SummaryResource.Resource := 'customers/summary';
with SummaryResource.ResourceDataSets.Add do
begin
  DataSetName := 'Customers';
  DataSet := CustomersTable;   // TVirtualTable
end;
with SummaryResource.ResourceDataSets.Add do
begin
  DataSetName := 'Cities';
  DataSet := CitiesTable;
end;

SummaryResource.GET; // CustomersTable and CitiesTable are filled and open

Each item has:

Property	Default	Meaning
DataSetName		The name of the dataset in the response (the member of the JSON object).
DataSet		The TVirtualTable to fill: its fields come from the response (types and sizes as on the server).
SendData	False	POST sends this dataset.
Synchronize	True	Fill the dataset in the main thread (GETAsync from another thread updates bound controls safely).

A GET adds an item for a dataset of the response that has none (without a DataSet, to fill later) and removes the items of the datasets missing from the response.

Sending data back

The Devart libraries have no delta of the changes: POST sends the whole datasets of the items with SendData = True, in the native format, and the server inserts or updates their records (see Receiving datasets in the page of each library: the server decides what to do with them, i.e. an upsert by key). The response of the server, if JSON, is in POSTResponse:

ImportResource := TMARSMyDACResource.Create(Self);
ImportResource.Application := MARSApplication;
ImportResource.Resource := 'customers/import';
ImportResource.SpecificAccept := 'application/json'; // the server answers with a JSON object
with ImportResource.ResourceDataSets.Add do
begin
  DataSetName := 'Customers';
  DataSet := CustomersTable;
  SendData := True;
end;

ImportResource.POST;
ShowMessage((ImportResource.POSTResponse as TJSONObject).ReadIntegerValue('imported').ToString);

Records added on the client usually have no key (it is assigned by the database): the server inserts them, the next GET brings back their keys. Records deleted on the client are not in the data sent, so a server that only inserts and updates does not delete them: give the client a DELETE endpoint for that.

Single-dataset resource

TMARS…DataSetResource binds one TVirtualTable (DataSet) to a resource that returns one dataset: GET fills it with the first dataset of the response, POST sends it when SendData is True.

CustomerResource := TMARSIBDACDataSetResource.Create(Self);
CustomerResource.Application := MARSApplication;
CustomerResource.Resource := 'customers/1';
CustomerResource.DataSet := CustomerTable;
CustomerResource.GET;

Plain JSON

Any client can read the same resources as plain JSON (Accept: application/json, an array of records): use TMARSClientResourceJSON when you need JSON objects rather than datasets, or a resource of yours with GETAsString.

See also

• Data Access: the model on the server.
• UniDACDemo, MyDACDemo, IBDACDemo: the FMX client of each demo loads, edits and saves the customers with these components.
• FireDAC Client: the same with FireDAC, which has deltas.