Note: MySQL and Java DB currently do not support the RowId
JDBC interface. Consequently, no JDBC tutorial example is available to demonstrate the features described in this section.
A RowId
object represents an address to a row in a database table. Note, however, that the ROWID
type is not a standard SQL type. ROWID
values can be useful because they are typically the fastest way to access a single row and are unique identifies for rows in a table. However, you should not use a ROWID
value as the primary key of a table. For example, if you delete a particular row from a table, a database might reassign its ROWID
value to a row inserted later.
The following topics are covered:
Retrieve a java.sql.RowId
object by calling the getter methods defined in the interfaces ResultSet
and CallableStatement
. The RowId
object that is returned is an immutable object that you can use for subsequent referrals as a unique identifier to a row. The following is an example of calling the ResultSet.getRorId
method:
java.sql.RowId rowId_1 = rs.getRowId(1);
You can set a RowId
object as a parameter in a parameterized PreparedStatement
object:
Connection conn = ds.getConnection( username, password); PreparedStatement ps = conn.prepareStatement( "INSERT INTO BOOKLIST" + "(ID, AUTHOR, TITLE, ISBN) " + "VALUES (?, ?, ?, ?)"); ps.setRowId(1, rowId_1);
You can also update a column with a specific RowId
object in an updatable ResultSet
object:
ResultSet rs = ... rs.next(); rs.updateRowId(1, rowId_1);
A RowId
object value is typically not portable between data sources and should be considered as specific to the data source when using the set or update method in PreparedStatement
and ResultSet
objects, respectively. It is therefore inadvisable to get a RowId
object from a ResultSet
object with a connection to one data source and then attempt to use the same RowId
object in a unrelated ResultSet
object with a connection to a different data source.
A RowId
object is valid as long as the identified row is not deleted and the lifetime of the RowId
object is within the bounds of the lifetime specified by that the data source for the RowId
.
To determine the lifetime of RowId
objects of your database or data source, call the method DatabaseMetaData.getRowIdLifetime
. It returns a value of a RowIdLifetime
enumerated data type. The following method JDBCTutorialUtilities.rowIdLifeTime
returns the lifetime of RowId
objects:
public static void rowIdLifetime(Connection conn) throws SQLException { DatabaseMetaData dbMetaData = conn.getMetaData(); RowIdLifetime lifetime = dbMetaData.getRowIdLifetime(); switch (lifetime) { case ROWID_UNSUPPORTED: System.out.println( "ROWID type not supported"); break; case ROWID_VALID_FOREVER: System.out.println( "ROWID has unlimited lifetime"); break; case ROWID_VALID_OTHER: System.out.println( "ROWID has indeterminate lifetime"); break; case ROWID_VALID_SESSION: System.out.println( "ROWID type has lifetime that " + "is valid for at least the " + "containing session"); break; case ROWID_VALID_TRANSACTION: System.out.println( "ROWID type has lifetime that " + "is valid for at least the " + "containing transaction"); } }