Package org.datanucleus.store.rdbms.sql

Class UnionStatementGenerator

  • All Implemented Interfaces:
    SelectStatementGenerator
    public class UnionStatementGenerator
extends AbstractSelectStatementGenerator
    Class to generate a SelectStatement 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
    • selectDnType : adds a SELECT of a dummy column accessible as "DN_TYPE" storing the class name.
    • allowNulls : whether we allow for null objects (only happens when we have a join table collection.

    • Field Detail

      • DN_TYPE_COLUMN

        public static final String DN_TYPE_COLUMN
        Name of column added when using "selectDnType"
        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 DN_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 DN_TYPE] 
 FROM A THIS
   INNER JOIN A1 'ELEMENT' ON 'ELEMENT'.A1_ID = THIS.A_ID

 UNION

 SELECT ['mydomain.A2' AS DN_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 DN_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 DN_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 DN_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: SelectStatementGenerator
        Method to set the parent statement. Must be set before calling getStatement().
        Parameters:
        stmt - The parent statement

      • getStatement

        public SelectStatement getStatement​(org.datanucleus.ExecutionContext ec)
        Accessor for the SelectStatement for the candidate [+ subclasses].
        Parameters:
        ec - ExecutionContext
        Returns:
        The SelectStatement returning objects with a UNION statement.

      • getSelectStatementForCandidate

        protected SelectStatement getSelectStatementForCandidate​(String className,
                                                         org.datanucleus.ExecutionContext ec)
        Convenience method to return the SelectStatement for a particular class. Returns a SelectStatement 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
        ec - ExecutionContext
        Returns:
        The SelectStatement

      • getSQLStatementForCandidateViaJoin

        protected SelectStatement 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