org.datanucleus.store.rdbms.sql

Class UnionStatementGenerator

java.lang.Object

org.datanucleus.store.rdbms.sql.AbstractStatementGenerator

org.datanucleus.store.rdbms.sql.UnionStatementGenerator

All Implemented Interfaces:

StatementGenerator

public class UnionStatementGenerator
extends AbstractStatementGenerator

Class to generate an SQLStatement for iterating through instances of a particular type (and optionally subclasses). Based around the candidate type having subclasses and we use UNIONs to return all possible types of candidate. Also allows select of a dummy column to return the type for the part of the UNION that the object came from. Please refer to the specific constructors for the usages.

Supported options

This generator supports

• selectNucleusType : adds a SELECT of a dummy column accessible as "NUCLEUS_TYPE" storing the class name.
• allowNulls : whether we allow for null objects (only happens when we have a join table collection.

Field Summary

Fields

Modifier and Type	Field and Description
static String	NUC_TYPE_COLUMN Name of column added when using "selectNucleusType"

Fields inherited from class org.datanucleus.store.rdbms.sql.AbstractStatementGenerator

candidateTable, candidateTableAlias, candidateTableGroupName, candidateType, clr, includeSubclasses, parentStmt, storeMgr

Fields inherited from interface org.datanucleus.store.rdbms.sql.StatementGenerator

OPTION_ALLOW_NULLS, OPTION_RESTRICT_DISCRIM, OPTION_SELECT_NUCLEUS_TYPE

Constructor Summary

Constructors

Constructor and Description
UnionStatementGenerator(RDBMSStoreManager storeMgr, org.datanucleus.ClassLoaderResolver clr, Class candidateType, boolean includeSubclasses, DatastoreIdentifier candidateTableAlias, String candidateTableGroupName) Constructor using the candidateTable as the primary table.
UnionStatementGenerator(RDBMSStoreManager storeMgr, org.datanucleus.ClassLoaderResolver clr, Class candidateType, boolean includeSubclasses, DatastoreIdentifier candidateTableAlias, String candidateTableGroupName, Table joinTable, DatastoreIdentifier joinTableAlias, JavaTypeMapping joinElementMapping) Constructor using a join table as the primary table.

Method Summary

Modifier and Type	Method and Description
protected SQLStatement	getSQLStatementForCandidate(String className) Convenience method to return the SQLStatement for a particular class.
protected SQLStatement	getSQLStatementForCandidateViaJoin(String className) Convenience method to return the SQLStatement for a particular class selecting a join table.
SQLStatement	getStatement() Accessor for the SQL Statement for the candidate [+ subclasses].
void	setParentStatement(SQLStatement stmt) Method to set the parent statement.

Methods inherited from class org.datanucleus.store.rdbms.sql.AbstractStatementGenerator

hasOption, setOption, unsetOption

Methods inherited from class java.lang.Object

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

Field Detail

NUC_TYPE_COLUMN

public static final String NUC_TYPE_COLUMN

Name of column added when using "selectNucleusType"

See Also:

Constant Field Values

Constructor Detail

UnionStatementGenerator

public UnionStatementGenerator(RDBMSStoreManager storeMgr,
                               org.datanucleus.ClassLoaderResolver clr,
                               Class candidateType,
                               boolean includeSubclasses,
                               DatastoreIdentifier candidateTableAlias,
                               String candidateTableGroupName)

Constructor using the candidateTable as the primary table. If we are querying objects of type A with subclasses A1, A2 the query will be of the form :-

 SELECT ['mydomain.A' AS NUCLEUS_TYPE]
 FROM A THIS
   LEFT OUTER JOIN A1 SUBELEMENT0 ON SUBELEMENT0.A1_ID = THIS.A_ID
   LEFT OUTER JOIN A1 SUBELEMENT1 ON SUBELEMENT0.A2_ID = THIS.A_ID
 WHERE SUBELEMENT0.A1_ID IS NULL
 AND SUBELEMENT0.A2_ID IS NULL

 UNION 

 SELECT ['mydomain.A1' AS NUCLEUS_TYPE] 
 FROM A THIS
   INNER JOIN A1 'ELEMENT' ON 'ELEMENT'.A1_ID = THIS.A_ID

 UNION

 SELECT ['mydomain.A2' AS NUCLEUS_TYPE] 
 FROM A THIS
   INNER JOIN A2 'ELEMENT' ON 'ELEMENT'.A2_ID = THIS.A_ID
 

So the first part of the UNION returns the objects just present in the A table, whilst the second part returns those just in table A1, and the third part returns those just in table A2.

Parameters:

storeMgr - the store manager

clr - ClassLoader resolver

candidateType - the candidate that we are looking for

includeSubclasses - if the subclasses of the candidate should be included in the result

candidateTableAlias - Alias to use for the candidate table (optional)

candidateTableGroupName - Name of the table group for the candidate(s) (optional)

UnionStatementGenerator

public UnionStatementGenerator(RDBMSStoreManager storeMgr,
                               org.datanucleus.ClassLoaderResolver clr,
                               Class candidateType,
                               boolean includeSubclasses,
                               DatastoreIdentifier candidateTableAlias,
                               String candidateTableGroupName,
                               Table joinTable,
                               DatastoreIdentifier joinTableAlias,
                               JavaTypeMapping joinElementMapping)

Constructor using a join table as the primary table. If we are querying elements (B) of a collection in class A and B has subclasses B1, B2 stored via a join table (A_B) the query will be of the form :-

 SELECT ['mydomain.B' AS NUCLEUS_TYPE]
 FROM A_B T0
   INNER JOIN B T1 ON T0.B_ID_EID = T1.B_ID
   LEFT OUTER JOIN B1 T2 ON T2.B1_ID = T0.B_ID_EID
   LEFT OUTER JOIN B2 T3 ON T3.B2_ID = T0.B_ID_EID
 WHERE T2.B1_ID IS NULL
 AND T3.B2_ID IS NULL

 UNION 

 SELECT ['mydomain.B1' AS NUCLEUS_TYPE] 
 FROM A_B THIS
   INNER JOIN B T1 ON T1.B_ID = T0.B_ID_EID
   INNER JOIN B1 T2 ON T2.B1_ID = T1.B_ID

 UNION

 SELECT ['mydomain.A2' AS NUCLEUS_TYPE] 
 FROM A_B THIS
   INNER JOIN B T1 ON T1.B_ID = T0.B_ID_EID
   INNER JOIN B2 T2 ON T2.B2_ID = T1.B_ID
 

So the first part of the UNION returns the objects just present in the B table, whilst the second part returns those just in table B1, and the third part returns those just in table B2. When we have a join table collection we MUST select the join table since this then caters for the situation of having null elements (if we had selected the root element table we wouldn't know if there was a null element in the collection).

Parameters:

storeMgr - the store manager

clr - ClassLoader resolver

candidateType - the candidate that we are looking for

includeSubclasses - if the subclasses of the candidate should be included in the result

candidateTableAlias - Alias to use for the candidate table (optional)

candidateTableGroupName - Name of the table group for the candidate(s) (optional)

joinTable - Join table linking owner to elements

joinTableAlias - any alias to use for the join table in the SQL

joinElementMapping - Mapping in the join table to link to the element

Method Detail

setParentStatement

public void setParentStatement(SQLStatement stmt)

Description copied from interface: StatementGenerator

Method to set the parent statement. Must be set before calling getStatement().

Parameters:

stmt - The parent statement

getStatement

public SQLStatement getStatement()

Accessor for the SQL Statement for the candidate [+ subclasses].

Returns:

The SQL Statement returning objects with a UNION statement.

getSQLStatementForCandidate

protected SQLStatement getSQLStatementForCandidate(String className)

Convenience method to return the SQLStatement for a particular class. Returns a SQLStatement with primaryTable of the "candidateTable", and which joins to the table of the class (if different).

Parameters:

className - The class name to generate the statement for

Returns:

The SQLStatement

getSQLStatementForCandidateViaJoin

protected SQLStatement getSQLStatementForCandidateViaJoin(String className)

Convenience method to return the SQLStatement for a particular class selecting a join table. Returns a SQLStatement with primaryTable of the "joinTable", and which joins to the table of the class.

Parameters:

className - The class name to generate the statement for

Returns:

The SQLStatement