Translation of object queries involving inheritence
View Patent ↗Join expressions, expressed in terms of objects, are translated into a relational database join statement by generating a parse tree based on the join expression. The parse tree is traversed to build the relational database join statement.
1. A computer-implemented method for translating an object query identifying an entity to be queried, the entity having inheritance, into a relational database query for execution against a relational database, comprising:
identifying associated entities in an inheritance hierarchy associated with the entity to be queried, wherein identifying associated entities comprises constructing a tree having nodes corresponding to ancestors and descendents of the entity to be queried in the inheritance hierarchy;
grouping associated entities that are mapped to a common table in the relational database, wherein grouping comprises traversing the tree, grouping nodes of the tree where entities in the nodes are mapped to a common table, to form an entity group tree, and wherein grouping further comprises repeating the steps of constructing a tree and traversing the tree until the entity group tree stabilizes; and
building one or more query statements based on the groups.
2. The computer-implemented method of claim 1 wherein traversing the tree comprises:
traversing the tree in prefix order.
3. The computer-implemented method of claim 2 wherein grouping nodes comprises:
merging parent and child nodes having entities that are mapped to a common table.
4. The computer-implemented method of claim 3 wherein grouping nodes comprises:
merging children nodes of an identified parent node where the children nodes have entities that are mapped to a common table.
5. The computer-implemented method of claim 4 wherein building one or more query statements comprises:
building a query statement for each entity in the entity group tree; and
adding the query statement to a statement list.
6. The computer-implemented method of claim 5 wherein building one or more query statements comprises:
if more than one query statement is on the statement list, joining the query statements with a relational database operator producing a union of the query statements.
7. The computer-implemented method of claim 6 wherein building a query statement for each entity in the entity group tree comprises:
generating a statement with an indicator identifying the statement;
adding to the generated statement a column name identifying table columns from the concrete entity to be returned; and
adding a column name identifying table columns from ancestor and descendent nodes in the inheritance hierarchy.
8. The computer-implemented method of claim 7 wherein adding a column name identifying columns from ancestor and descendent nodes comprises:
adding to the generated statement name of table columns for a least-derived node in the inheritance hierarchy.
9. The computer-implemented method of claim 8 wherein adding a column name identifying columns from ancestor and descendent nodes comprises:
adding to the generated statement name of table columns for all additional ancestor nodes in the inheritance hierarchy.
10. The computer-implemented method of claim 9 wherein adding a column name identifying columns from ancestor and descendent nodes comprises:
adding to the generated statement name of table columns for descendent nodes in the inheritance hierarchy.
11. The computer-implemented method of claim 10 wherein building a query statement for each concrete entity comprises:
adding restrictions specified in the object query to the query statement.
12. A computer readable medium storing instructions which, when executed, cause a computer to perform a translation of an object query that identifies an entity to be queried, the entity to be queried having inheritance, into a relational database query for execution against a relational database, by performing the steps of:
identifying associated entities in an inheritance hierarchy associated with the entity to be queried, wherein identifying associated entities comprises constructing a tree having nodes corresponding to ancestors and descendents of the entity to be queried in the inheritance hierarchy;
grouping associated entities that are mapped to a common table in the relational database into groups, wherein grouping comprises traversing the tree, grouping nodes of the tree when entities in the nodes are mapped to a common table, to form an entity group tree, and wherein grouping further comprises repeating the steps of constructing a tree and traversing the tree until the entity group tree stabilizes; and
building one or more query statements based on the groups.
13. The computer readable medium of claim 12 wherein traversing the tree comprises:
traversing the tree in prefix order.
14. The computer readable medium of claim 13 wherein grouping nodes comprises:
merging parent and child nodes having entities that are mapped to a common table.
15. The computer readable medium of claim 14 wherein grouping nodes comprises:
merging children nodes of an identified parent node where the children nodes have entities that are mapped to a common table.
16. The computer readable medium of claim 15 wherein building one or more query statements comprises:
building a query statement for entity group tree that has at least one concrete entity; and
adding the query statement to a statement list.
17. The computer readable medium of claim 16 wherein building one or more query statements comprises:
if more than one query statement is on the statement list, joining the query statements with a relational database operator producing a union of the query statements.
18. The computer readable medium of claim 17 wherein building a query statement for each entity group tree comprises:
generating a statement with an indicator identifying the statement;
adding to the generated statement a column name identifying table columns from the concrete entity to be returned; and
adding a column name identifying table columns from ancestor and descendent nodes in the entity group tree.
19. The computer readable medium of claim 18 wherein adding a column name identifying columns from ancestor and descendent nodes comprises:
adding to the generated statement an name of table columns for a least-derived node in the entity group tree.
20. The computer readable medium of claim 19 wherein adding a column name identifying columns from ancestor and descendent nodes comprises:
adding to the generated statement name of table columns for all additional ancestor nodes in the entity group tree.
21. The computer readable medium of claim 20 wherein adding a column name identifying columns from ancestor and descendent nodes comprises:
adding to the generated statement name of table columns for descendent nodes in the entity group tree.
22. The computer readable medium of claim 18 wherein building a query statement for each concrete entity comprises:
adding restrictions specified in the object query to the query statement.