The object DatabaseMetadata of the Polypheny JDBC driver provides methods to query properties of the DBMS, properties of namespaces as well as the supported functions of the driver and Polypheny.
This section documents the basic metadata functions.
supportsResultSetHoldability
public boolean supportsResultSetHoldability( int resultSetHoldability )
throws SQLException
This method evaluates whether a specific result set holdability is supported by Polypheny. The holdability of a result set determines its behavior when a transaction gets committed.
For now, the sole holdability mode supported is ResultSet.CLOSE_CURSORS_AT_COMMIT.
Parameters:
| Parameter | Type | Description |
|---|---|---|
| resultSetHoldability | int | The holdability mode to be inspected. Expected to be a ResultSet holdability constant, e.g., ResultSet.HOLD_CURSORS_OVER_COMMIT or ResultSet.CLOSE_CURSORS_AT_COMMIT. |
Returns:
| Return Type | Description |
|---|---|
| boolean | If the provided holdability mode is supported by the DBMS, it returns true. Given the constraints of the current system, it will yield true only for the ResultSet.CLOSE_CURSORS_AT_COMMIT constant. Any other holdability mode will result in false. |
Throws:
- SQLException: In cases where a database access error materializes during the support check.
getResultSetHoldability
The getResultSetHoldability() method retrieves the default result set holdability for ResultSet objects generated from this Statement object. Holdability defines the behavior of cursors when transactions are committed. In the context of this method, the default behavior is to close cursors when a transaction commits.
public int getResultSetHoldability() throws SQLException
Returns:
| Return Type | Description | Default Value |
|---|---|---|
| int | The holdability of ResultSet objects. |
ResultSet.CLOSE_CURSORS_AT_COMMIT |
Throws:
- SQLException: Thrown if a database access error occurs or the method is called on a closed connection.
getDatabaseMajorVersion and getDatabaseMinorVersion
The database version is commonly represented as a combination of major and minor version numbers. The getDatabaseMajorVersion() and getDatabaseMinorVersion() methods provide access to these numbers, respectively.
public int getDatabaseMajorVersion() throws SQLException
Fetches the major version number of the underlying database.
Returns:
| Return Type | Description |
|---|---|
| int | The major version number of the database. |
Throws:
- SQLException: Thrown if a database access error occurs or the method is called on a closed connection.
public int getDatabaseMinorVersion() throws SQLException
Fetches the minor version number of the underlying database.
Returns:
| Return Type | Description |
|---|---|
| int | The minor version number of the database. |
Throws:
- SQLException: Thrown if a database access error occurs or the method is called on a closed connection.
getJDBCMajorVersion and getJDBCMinorVersion
JDBC versions are typically denoted by a major and minor version number. The getJDBCMajorVersion() and getJDBCMinorVersion() methods provide access to these version numbers, respectively.
public int getJDBCMajorVersion() throws SQLException
Retrieves the major version number of the JDBC driver.
Returns:
| Return Type | Description |
|---|---|
| int | The major version number of the JDBC driver. |
Throws:
- SQLException: Thrown if a database access error occurs or the method is called on a closed connection.
public int getJDBCMinorVersion() throws SQLException
Retrieves the minor version number of the JDBC driver.
Returns:
| Return Type | Description |
|---|---|
| int | The minor version number of the JDBC driver. |
Throws:
- SQLException: Thrown if a database access error occurs or the method is called on a closed connection.
Usage Example:
DatabaseMetaData dbmd = connection.getMetaData();
int jdbcMajorVersion = dbmd.getJDBCMajorVersion();
int jdbcMinorVersion = dbmd.getJDBCMinorVersion();
System.out.println( "Using JDBC driver version: " + jdbcMajorVersion + "." + jdbcMinorVersion );
unwrap
The unwrap method attempts to retrieve an instance of the desired interface that might be a wrapper around the invoked object. If the current object is an instance of the specified class, it returns the object cast to that type.
@Override
public <T> T unwrap( Class<T> aClass ) throws SQLException
Parameters:
| Parameter | Type | Description |
|---|---|---|
| aClass | Class<T> |
The type of the class that the current instance is to be unwrapped as. |
Returns:
| Return Type | Description |
|---|---|
| T | The current instance unwrapped as the specified class if possible. |
Throws:
- SQLException: Thrown when the current object isn’t a wrapper for the specified class.
Usage Example:
try {
DatabaseMetaData dbmd = connection.getMetaData();
PolyphenyDatabaseMetadata polyphenyDbmd = dbmd.unwrap( PolyphenyDatabaseMetadata.class );
} catch ( SQLException e ) {
System.out.println( e.getMessage() );
}
isWrapperFor
The isWrapperFor method checks if the current object is a wrapper for the specified class. It can be used to determine if calling unwrap with the specified class would succeed.
@Override
public boolean isWrapperFor( Class<?> aClass )
Parameters:
| Parameter | Type | Description |
|---|---|---|
| aClass | Class<?> |
The type of the class to check against the current instance. |
Returns:
| Return Type | Description |
|---|---|
| boolean | true if the current object is a wrapper for the specified class, false otherwise. |
Usage Example:
DatabaseMetaData dbmd = connection.getMetaData();
if ( dbmd.isWrapperFor( PolyphenyDatabaseMetadata.class ) ) {
PolyphenyDatabaseMetadata instance = myObject.unwrap( PolyphenyDatabaseMetadata.class );
} else {
System.out.println( "Not a wrapper for PolyphenyDatabaseMetadata." );
}
