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DataBind Controls to OData Services in C++Builder

DataBind to OData services in C++Builder with standard components and controls.

The CData ODBC Driver for OData makes it easy to integrate connectivity to live OData services with standard data access components in C++Builder. This article shows how to create a simple visual component library (VCL) application in C++Builder that connects to OData services, executes queries, and displays the results in a grid. An additional section shows how to use FireDAC components to execute commands from code.

Create a FireDAC Connection to OData Services

If you have not already, first specify connection properties in an ODBC DSN (data source name). This is the last step of the driver installation. You can use the Microsoft ODBC Data Source Administrator to create and configure ODBC DSNs.

The User and Password properties, under the Authentication section, must be set to valid OData user credentials. In addition, you will need to specify a URL to a valid OData server organization root or OData services file.

You can then follow the steps below to use the Data Explorer to create a FireDAC connection to OData.

  1. In a new VCL Forms application, expand the FireDAC node in the Data Explorer.
  2. Right-click the ODBC Data Source node in the Data Explorer.
  3. Click Add New Connection.
  4. Enter a name for the connection.
  5. In the FireDAC Connection Editor that appears, set the DataSource property to the name of the ODBC DSN for OData.

Create VCL Applications with Connectivity to OData Services

Follow the procedure below to start querying OData services from a simple VCL application that displays the results of a query in a grid.

  1. Drop a TFDConnection component onto the form and set the following properties:

    • ConnectionDefName: Select the FireDAC connection to OData.
    • Connected: Select True from the menu and, in the dialog that appears, enter your credentials.
  2. Drop a TFDQuery component onto the form and set the properties below:

    • Connection: Set this property to the TFDConnection component, if this component is not already specified.
    • SQL: Click the button in the SQL property and enter a query. For example:

      SELECT Orders.Freight, Customers.ContactName FROM Customers INNER JOIN Orders ON Customers.CustomerId=Orders.CustomerId
    • Active: Set this property to true.
  3. Drop a TDataSource component onto the form and set the following property:

    • DataSet: In the menu for this property, select the name of the TFDQuery component.
  4. Drop a TDBGrid control onto the form and set the following property:

    • DataSource: Select the name of the TDataSource.
  5. Drop a TFDGUIxWaitCursor onto the form — this is required to avoid a run-time error.

Execute Commands to OData with FireDAC Components

You can use the TFDConnection and TFQuery components to execute queries to OData services. This section provides OData-specific examples of executing queries with the TFQuery component.

Connect to OData Services

To connect to the data source, set the Connected property of the TFDConnection component to true. You can set the same properties from code:

FDConnection1->ConnectionDefName = "CData OData ODBC Source"; FDConnection1->Connected = true;

To connect the TFDQuery component to OData services, set the Connection property of the component. When a TFDQuery component is added at design time, its Connection property is automatically set to point to a TFDConnection on the form, as in the application above.

Create Parameterized Queries

To create a parameterized query, use the following syntax below:

FDQuery1->SQL->Text = "select * from Orders where shipcity = :ShipCity"; FDQuery1->ParamByName("shipcity")->AsString = "New York"; query->Open();

The example above binds a string-type input parameter by name and then opens the dataset that results.

Prepare the Statement

Preparing statements is costly in system resources and time. The connection must be active and open while a statement is prepared. By default, FireDAC prepares the query to avoid recompiling the same query over and over. To disable statement preparation, set ResourceOptions.DirectExecute to True; for example, when you need to execute a query only once.

Execute a Query

To execute a query that returns a result set, such as a select query, use the Open method. The Open method executes the query, returns the result set, and opens it. The Open method will return an error if the query does not produce a result set.

FDQuery1->SQL->Text := "select * from Orders where shipcity = :ShipCity"; FDQuery1.ParamByName("shipcity")->AsString = "New York"; FDQuery1->Open();

To execute a query that does not return a result set, use the ExecSQL method. The ExecSQL method will return an error if the query returns a result set. To retrieve the count of affected rows use the TFD.RowsAffected property.

FDQ.SQL.Text := "delete from Orders where Id = :Id"; FDQuery1->Params->Items[0]->AsString = "x12345"; FDQuery1->ExecSQL(); AnsiString i = FDQuery1->RowsAffected;