Extending HQL with Plain Recursive Facilities

The mismatch between relational databases and object-oriented programming languages has been significantly mitigated by the use of object-relational mapping. However, the querying facilities available in such mapping systems are still inferior when compared to the features of a fully-fledged relational DBMS. In our research we aim at enriching object-relation mapping with advanced database concepts. An example of such an aspect is recursive querying. In prequel papers we have shown how to extend Hibernates mapping configurations with comprehendible recursive views that map to SQL common table expressions. In this paper we show how one can extend Hibernate Query Language (HQL) with plain recursive query facilities based on Oracles CONNECT BY phrase. Although, unfortunately it has not become a part of the SQL standard, its properties like cleanness and guaranteed stop make it worth exploiting.We propose adding CONNECT BY to HQL.We have implemented a prototype mapping of this phrase to recursive queries in major DBMSs and tested its efficiency. As the result we have got a simple, safe and fast way to pose recursive queries in HQL.

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