Package org.datanucleus.store.rdbms.query

Class BulkFetchExistsHandler

java.lang.Object

org.datanucleus.store.rdbms.query.BulkFetchExistsHandler

All Implemented Interfaces:

BulkFetchHandler

public class BulkFetchExistsHandler
extends Object
implements BulkFetchHandler

Bulk-Fetch handler to generate the necessary statement for multi-valued field bulk-fetch using EXISTS subquery 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 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	Description
BulkFetchExistsHandler()

Method Summary

Modifier and Type	Method	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

Constructor Detail

BulkFetchExistsHandler

public BulkFetchExistsHandler()

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

parameters - Parameters for the query

mmd - Metadata for the multi-valued field

datastoreCompilation - The datastore compilation of the query

mapperOptions - Any options for the query to SQL mapper

query - The query

Returns:

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