net.spy.db
Class GetPK

java.lang.Object
  net.spy.SpyObject
      net.spy.db.GetPK

public class GetPK
extends SpyObject

Primary key generator. This is an extensible singleton that provides access to a database-backed set of primary keys along with a fetch-ahead cache of those keys.

The default implementation assumes you have the following table (primary_key) in the database the configuration defines:

primary_keys
Column Name	Column Type	Column Description
table_name	varchar	The name of the table (or other resource) for which we are generating the given primary key. All table names in this column must be in lowercase as the input from the user will be lowercased on key retrieval.
primary_key	numeric	The next primary key value issued.
incr_value	numeric	The amount to increment the primary key each time.

Other schemas may exist as long as they fit into the ``update something, select something'' model and they operate as described below.

Constructor Summary

protected

GetPK() Constructor for an extensible Singleton.

Method Summary

static GetPK	getInstance() Get the instance of GetPK.
BigDecimal	getPrimaryKey(SpyConfig conf, String table) Get a primary key from the database described in the given config.
protected DBSP	getSelectDBSP(Connection conn) Get the DBSP required for selecting primary key information back out of the primary key table.
protected DBSP	getUpdateDBSP(Connection conn) Get the DBSP required for updating the primary key table.
static void	setInstance(GetPK to) Set the singleton instance.

Methods inherited from class net.spy.SpyObject

getLogger

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GetPK

protected GetPK()

Constructor for an extensible Singleton.

Method Detail

getInstance

public static GetPK getInstance()

Get the instance of GetPK.

Returns:

the instance

setInstance

public static void setInstance(GetPK to)

Set the singleton instance.

Parameters:

to - the new singleton instance

getPrimaryKey

public BigDecimal getPrimaryKey(SpyConfig conf,
                                String table)
                         throws SQLException

Get a primary key from the database described in the given config.

Parameters:

conf - the configuration

table - the table for which the key is needed

Returns:

the key

Throws:

SQLException - if there's a problem getting the key

getUpdateDBSP

protected DBSP getUpdateDBSP(Connection conn)
                      throws SQLException

Get the DBSP required for updating the primary key table.

A subclass may override this to change the behavior of the first part of the ``fetch from db'' stage. The DBSP returned will take exactly one parameter: table_name and will be called via executeUpdate. The update must update exactly one row. Any more or fewer will cause the process to fail and an exception will be thrown.

For an example implementation, please see UpdatePrimaryKey (this is the default).

Parameters:

conn - the connection to use (already in a transaction)

Returns:

the required DBSP

Throws:

SQLException - if there's a problem getting the DBSP

getSelectDBSP

protected DBSP getSelectDBSP(Connection conn)
                      throws SQLException

Get the DBSP required for selecting primary key information back out of the primary key table.

A subclass may override this method to change the behavior of the select statement that finds the range of results for a table. The DBSP returned will take exactly one parameter: table_name and return a result set containing at least the following two columns:

• first_key - the first key in the range
• last_key - the last key in the range

The ResultSet must contain exactly one row. Any more or fewer will cause the process to fail and an exception will be thrown.

For an example implementation, please see SelectPrimaryKey (this is the default).

Parameters:

conn - the connection to use (already in a transaction)

Returns:

the required DBSP

Throws:

SQLException - if there's a problem getting the DBSP