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Avro ODBC Driver

Avro ODBC Driver は、ODBC 接続をサポートする任意のアプリケーションからAvro のリアルタイムなデータに直接接続できるパワフルなツールです。

標準ODBC Driver インターフェースを使い、データベース感覚でAvro データにアクセスできます。

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DataBind Controls to Avro Data in C++Builder


DataBind to Avro data in C++ Builder with standard components and controls.

The CData ODBC Driver for Avro makes it easy to integrate connectivity to live Avro data 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 Avro data, 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 Avro Data

Follow the steps below to use the Data Explorer to create a FireDAC connection to Avro.

  1. If you have not already, specify connection properties in a DSN (data source name). You can use the Microsoft ODBC Data Source Administrator to create and configure ODBC DSNs.

    Below is a typical connection string:

    URI=C:/folder/table.avro

    See the "Getting Started" chapter in the help documentation for a guide to setting the required properties in the Microsoft ODBC Data Source Administrator.

  2. In a new VCL Forms application, expand the FireDAC node in the Data Explorer.
  3. Right-click the ODBC Data Source node in the Data Explorer.
  4. Click Add New Connection.
  5. Enter a name for the connection.
  6. In the FireDAC Connection Editor that appears, set the DataSource property to the name of the ODBC DSN for Avro.
A FireDAC connection to the ODBC data source. (Salesforce is shown.)

Create VCL Applications with Connectivity to Avro Data

Follow the procedure below to start querying Avro data 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 Avro.
    • 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 * FROM SampleTable_1
    • 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.
Components in FireDAC used to databind an editable grid to the data source. (Salesforce is shown.)

Execute Commands to Avro with FireDAC Components

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

Connect to Avro Data

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 Avro ODBC Source"; FDConnection1->Connected = true;

To connect the TFDQuery component to Avro data, 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 SampleTable_1 where column2 = :Column2"; FDQuery1->ParamByName("column2")->AsString = "value_2"; 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 SampleTable_1 where column2 = :Column2"; FDQuery1.ParamByName("column2")->AsString = "value_2"; FDQuery1->Open();