XQConnection

A connection (session) with a specific XQuery engine. Connections are obtained through an XQDataSource object.

XQuery expressions are executed and results are returned within the context of a connection. They are either executed through XQExpression or XQPreparedExpression objects.

  XQDataSource ds;// obtain the XQuery datasource
  ... 
  XQConnection conn = ds.getConnection();

  XQPreparedExpression expr = conn.prepareExpression("for $i in ...");
  XQResultSequence result = expr.executeQuery();
  // - or - 
  XQExpression expr = conn.createExpression();
  XQSequence result = expr.executeQuery("for $i in..");

  // The sequence can now be iterated 
  while (result.next())
  { 
     String str  = result.getItemAsString();
     System.out.println(" output "+ str);
  }
  result.close();
  expr.close(); 
  conn.close();  // close the connection and free all resources..

A connection holds also default values for XQExpression and XQPreparedExpression properties. An application can override these defaults by passing an XQStaticContext object to the setStaticContext() method.

By default a connection operates in auto-commit mode, which means that each xquery is executed and committed in an individual transaction. If auto-commit mode is disabled, a transaction must be ended explicitly by the application calling commit() or rollback().

An XQConnection object can be created on top of an existing JDBC connection. If an XQConnection is created on top of the JDBC connection, it inherits the transaction context from the JDBC connection. Also, in this case, if the auto-commit mode is changed, or a transaction is ended using commit or rollback, it also changes the underlying JDBC connection.

An XQJ driver is not required to provide finalizer methods for the connection and other objects. Hence it is strongly recommended that users call close method explicitly to free any resources. It is also recommended that they do so under a final block to ensure that the object is closed even when there are exceptions. Not closing this object explicitly might result in serious memory leaks.

When the XQConnection is closed any XQExpression and XQPreparedExpression objects obtained from it are also implicitly closed.

Method Summary
void	close() Closes the connection.
void	commit() Makes all changes made in the current transaction permanent and releases any locks held by the datasource.
XQExpression	createExpression() Creates a new `XQExpression` object that can be used to perform execute immediate operations with XQuery expressions.
XQExpression	createExpression(XQStaticContext properties) Creates a new `XQExpression` object that can be used to perform execute immediate operations with XQuery expressions.
boolean	getAutoCommit() Gets the auto-commit attribute of this connection
XQMetaData	getMetaData() Gets the metadata for this connection.
XQStaticContext	getStaticContext() Gets an `XQStaticContext` representing the default values for all expression properties.
boolean	isClosed() Checks if the connection is closed.
XQPreparedExpression	prepareExpression(String xquery) Prepares an expression for execution.
XQPreparedExpression	prepareExpression(String xquery, XQStaticContext properties) Prepares an expression for execution.
XQPreparedExpression	prepareExpression(Reader xquery) Prepares an expression for execution.
XQPreparedExpression	prepareExpression(Reader xquery, XQStaticContext properties) Prepares an expression for execution.
XQPreparedExpression	prepareExpression(InputStream xquery) Prepares an expression for execution.
XQPreparedExpression	prepareExpression(InputStream xquery, XQStaticContext properties) Prepares an expression for execution.
void	rollback() Undoes all changes made in the current transaction and releases any locks held by the datasource.
void	setAutoCommit(boolean autoCommit) Sets the auto-commit attribute to the given state.
void	setStaticContext(XQStaticContext properties) Sets the default values for all expression properties.

Method Detail

Closes the connection. This also closes any XQExpression and XQPreparedExpression obtained from this connection. Once the connection is closed, no method other than close or the isClosed method may be called on the connection object. Calling close on an XQConnection object that is already closed has no effect. Note that an XQJ driver is not required to provide finalizer methods for the connection and other objects. Hence it is strongly recommended that users call this method explicitly to free any resources. It is also recommended that they do so under a final block to ensure that the object is closed even when there are exceptions.

Throws: XQException if there is an error during closing the connection.

commit

Makes all changes made in the current transaction permanent and releases any locks held by the datasource. This method should be used only when auto-commit mode is disabled. Any XQResultSequence, or XQResultItem may be implicitly closed upon commit, if the holdability property of the sequence is set to XQConstants.HOLDTYPE_CLOSE_CURSORS_AT_COMMIT.

Throws: XQException if the connection is in a closed state or this connection is operating in auto-commit mode

createExpression

Creates a new XQExpression object that can be used to perform execute immediate operations with XQuery expressions. The properties of the connection's default XQStaticContext are copied to the returned XQExpression.

Returns: XQExpression that can be used to execute multiple expressions

Throws: XQException if the connection is in a closed state

createExpression

Creates a new XQExpression object that can be used to perform execute immediate operations with XQuery expressions. The properties of the specified XQStaticContext values are copied to the returned XQExpression.

Parameters: properties XQStaticContext containing values of expression properties

Returns: XQExpression that can be used to execute multiple expressions

Throws: XQException if (1) the connection is in a closed state, or (2) the specified argument is null

getAutoCommit

getMetaData

getStaticContext

Gets an XQStaticContext representing the default values for all expression properties. In order to modify the defaults, it is not sufficient to modify the values in the returned XQStaticContext object; in addition setStaticContext should be called to make those new values effective.

Returns: XQStaticContext representing the default values for all expression properties

Throws: XQException if the connection is in a closed state

isClosed

prepareExpression