Spec-Zone .ru
спецификации, руководства, описания, API
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Spec-Zone .ru
спецификации, руководства, описания, API
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Before version 3.0 of the JDBC API, there was no standard way of retrieving key values from databases that
supported auto increment or identity columns. With older JDBC drivers for MySQL, you could always use a
MySQL-specific method on the Statement interface, or issue the query SELECT LAST_INSERT_ID() after issuing an INSERT to a table that had an AUTO_INCREMENT
key. Using the MySQL-specific method call isn't portable, and issuing a SELECT to get the AUTO_INCREMENT key's value
requires another round-trip to the database, which isn't as efficient as possible. The following code snippets
demonstrate the three different ways to retrieve AUTO_INCREMENT values. First, we
demonstrate the use of the new JDBC 3.0 method getGeneratedKeys() which is now the
preferred method to use if you need to retrieve AUTO_INCREMENT keys and have access
to JDBC 3.0. The second example shows how you can retrieve the same value using a standard SELECT LAST_INSERT_ID() query. The final example shows how updatable result sets
can retrieve the AUTO_INCREMENT value when using the insertRow()
method.
Example 22.8. Connector/J: Retrieving AUTO_INCREMENT column
valuesusing Statement.getGeneratedKeys()
Statement stmt = null; ResultSet rs = null; try { // // Create a Statement instance that we can use for // 'normal' result sets assuming you have a // Connection 'conn' to a MySQL database already // available stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_UPDATABLE); // // Issue the DDL queries for the table for this example // stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial"); stmt.executeUpdate( "CREATE TABLE autoIncTutorial (" + "priKey INT NOT NULL AUTO_INCREMENT, " + "dataField VARCHAR(64), PRIMARY KEY (priKey))"); // // Insert one row that will generate an AUTO INCREMENT // key in the 'priKey' field // stmt.executeUpdate( "INSERT INTO autoIncTutorial (dataField) " + "values ('Can I Get the Auto Increment Field?')", Statement.RETURN_GENERATED_KEYS); // // Example of using Statement.getGeneratedKeys() // to retrieve the value of an auto-increment // value // int autoIncKeyFromApi = -1; rs = stmt.getGeneratedKeys(); if (rs.next()) { autoIncKeyFromApi = rs.getInt(1); } else { // throw an exception from here } rs.close(); rs = null; System.out.println("Key returned from getGeneratedKeys():" + autoIncKeyFromApi);} finally { if (rs != null) { try { rs.close(); } catch (SQLException ex) { // ignore } } if (stmt != null) { try { stmt.close(); } catch (SQLException ex) { // ignore } }}
Example 22.9. Connector/J: Retrieving AUTO_INCREMENT column
valuesusing SELECT LAST_INSERT_ID()
Statement stmt = null; ResultSet rs = null; try { // // Create a Statement instance that we can use for // 'normal' result sets. stmt = conn.createStatement(); // // Issue the DDL queries for the table for this example // stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial"); stmt.executeUpdate( "CREATE TABLE autoIncTutorial (" + "priKey INT NOT NULL AUTO_INCREMENT, " + "dataField VARCHAR(64), PRIMARY KEY (priKey))"); // // Insert one row that will generate an AUTO INCREMENT // key in the 'priKey' field // stmt.executeUpdate( "INSERT INTO autoIncTutorial (dataField) " + "values ('Can I Get the Auto Increment Field?')"); // // Use the MySQL LAST_INSERT_ID() // function to do the same thing as getGeneratedKeys() // int autoIncKeyFromFunc = -1; rs = stmt.executeQuery("SELECT LAST_INSERT_ID()"); if (rs.next()) { autoIncKeyFromFunc = rs.getInt(1); } else { // throw an exception from here } rs.close(); System.out.println("Key returned from " + "'SELECT LAST_INSERT_ID()': " + autoIncKeyFromFunc);} finally { if (rs != null) { try { rs.close(); } catch (SQLException ex) { // ignore } } if (stmt != null) { try { stmt.close(); } catch (SQLException ex) { // ignore } }}
Example 22.10. Connector/J: Retrieving AUTO_INCREMENT column
valuesin Updatable ResultSets
Statement stmt = null; ResultSet rs = null; try { // // Create a Statement instance that we can use for // 'normal' result sets as well as an 'updatable' // one, assuming you have a Connection 'conn' to // a MySQL database already available // stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_UPDATABLE); // // Issue the DDL queries for the table for this example // stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial"); stmt.executeUpdate( "CREATE TABLE autoIncTutorial (" + "priKey INT NOT NULL AUTO_INCREMENT, " + "dataField VARCHAR(64), PRIMARY KEY (priKey))"); // // Example of retrieving an AUTO INCREMENT key // from an updatable result set // rs = stmt.executeQuery("SELECT priKey, dataField " + "FROM autoIncTutorial"); rs.moveToInsertRow(); rs.updateString("dataField", "AUTO INCREMENT here?"); rs.insertRow(); // // the driver adds rows at the end // rs.last(); // // We should now be on the row we just inserted // int autoIncKeyFromRS = rs.getInt("priKey"); rs.close(); rs = null; System.out.println("Key returned for inserted row: " + autoIncKeyFromRS);} finally { if (rs != null) { try { rs.close(); } catch (SQLException ex) { // ignore } } if (stmt != null) { try { stmt.close(); } catch (SQLException ex) { // ignore } }}
Running the preceding example code should produce the following output:
Key returned from getGeneratedKeys(): 1Key returned from SELECT LAST_INSERT_ID(): 1Key returned for inserted row: 2
At times, it can be tricky to use the SELECT LAST_INSERT_ID() query, as that
function's value is scoped to a connection. So, if some other query happens on the same connection, the value is
overwritten. On the other hand, the getGeneratedKeys() method is scoped by the
Statement instance, so it can be used even if other queries happen on the same
connection, but not on the same Statement instance.