org.datanucleus.store.rdbms.query

Class BulkFetchJoinHandler

java.lang.Object

org.datanucleus.store.rdbms.query.BulkFetchJoinHandler

All Implemented Interfaces:

BulkFetchHandler

public class BulkFetchJoinHandler
extends Object
implements BulkFetchHandler

Helper class to generate the necessary statement for multi-valued field bulk-fetch, using JOIN semantics.

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 CANDIDATE_TBL T1, ELEMENT_TBL ELEM WHERE ELEM.CAND_ID = T1.ID AND T1.COL2 = value

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 a JOIN, restricting to the candidates implied by the query This is work-in-progress

Constructor Summary

Constructors

Constructor and Description
BulkFetchJoinHandler()

Method Summary

Modifier and Type	Method and Description
IteratorStatement	getStatementToBulkFetchField(org.datanucleus.metadata.AbstractClassMetaData candidateCmd, org.datanucleus.metadata.AbstractMemberMetaData mmd, org.datanucleus.store.query.Query query, Map parameters, RDBMSQueryCompilation datastoreCompilation, Set<String> mapperOptions) 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

Methods inherited from interface org.datanucleus.store.rdbms.query.BulkFetchHandler

applyParametersToStatement

Constructor Detail

BulkFetchJoinHandler

public BulkFetchJoinHandler()

Method Detail

getStatementToBulkFetchField

public IteratorStatement getStatementToBulkFetchField(org.datanucleus.metadata.AbstractClassMetaData candidateCmd,
                                                      org.datanucleus.metadata.AbstractMemberMetaData mmd,
                                                      org.datanucleus.store.query.Query query,
                                                      Map parameters,
                                                      RDBMSQueryCompilation datastoreCompilation,
                                                      Set<String> mapperOptions)

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

Specified by:

getStatementToBulkFetchField in interface BulkFetchHandler

Parameters:

candidateCmd - Metadata for the candidate

mmd - Metadata for the member we are bulk-fetching the value(s) for

query - The query

parameters - Parameters for the query

datastoreCompilation - The datastore compilation of the query

mapperOptions - Any mapper options for query generation

Returns:

The statement to use for bulk fetching, together with mappings for extracting the results of the elements