org.datanucleus.store.rdbms.query

Class BulkFetchHelper

java.lang.Object

org.datanucleus.store.rdbms.query.BulkFetchHelper

public class BulkFetchHelper
extends Object

Helper class to generate the necessary statement for multi-valued field bulk-fetch. In simple terms if we have a query with resultant SQL like

SELECT COL1, COL2, COL3, ... FROM CANDIDATE_TBL T1 WHERE T1.COL2 = value

then to retrieve a multi-valued collection field of the candidate class it generates an SQL like

SELECT ELEM.COL1, ELEM.COL2, ... FROM ELEMENT_TBL ELEM WHERE EXISTS (
 SELECT T1.ID FROM CANDIDATE_TBL T1 WHERE T1.COL2 = value AND ELEM.OWNER_ID = T1.ID)

Obviously there are differences when using a join-table, or when the elements are embedded into the join-table, but the basic idea is we generate an iterator statement for the elements (just like the backing store normally would) except instead of restricting the statement to just a particular owner, it adds an EXISTS clause with the query as the exists subquery).

Constructor Summary

Constructors

Constructor and Description
BulkFetchHelper(org.datanucleus.store.query.Query q)

Method Summary

Modifier and Type	Method and Description
void	applyParametersToStatement(PreparedStatement ps, RDBMSQueryCompilation datastoreCompilation, SQLStatement sqlStmt, Map parameters) Convenience method to apply the passed parameters to the provided bulk-fetch statement.
IteratorStatement	getSQLStatementForContainerField(org.datanucleus.metadata.AbstractClassMetaData candidateCmd, Map parameters, org.datanucleus.metadata.AbstractMemberMetaData mmd, RDBMSQueryCompilation datastoreCompilation) Convenience method to generate a bulk-fetch statement for the specified multi-valued field of the owning query.

Methods inherited from class java.lang.Object

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

Constructor Detail

BulkFetchHelper

public BulkFetchHelper(org.datanucleus.store.query.Query q)

Method Detail

getSQLStatementForContainerField

public IteratorStatement getSQLStatementForContainerField(org.datanucleus.metadata.AbstractClassMetaData candidateCmd,
                                                          Map parameters,
                                                          org.datanucleus.metadata.AbstractMemberMetaData mmd,
                                                          RDBMSQueryCompilation datastoreCompilation)

Convenience method to generate a bulk-fetch statement for the specified multi-valued field of the owning query.

Parameters:

candidateCmd - Metadata for the candidate

parameters - Parameters for the query

mmd - Metadata for the multi-valued field

datastoreCompilation - The datastore compilation of the query

Returns:

The bulk-fetch statement for retrieving this multi-valued field.

applyParametersToStatement

public void applyParametersToStatement(PreparedStatement ps,
                                       RDBMSQueryCompilation datastoreCompilation,
                                       SQLStatement sqlStmt,
                                       Map parameters)

Convenience method to apply the passed parameters to the provided bulk-fetch statement. Takes care of applying parameters across any UNIONs of elements.

Parameters:

ps - PreparedStatement

datastoreCompilation - The datastore compilation for the query itself

sqlStmt - The bulk-fetch iterator statement

parameters - The map of parameters passed in to the query