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EclipseLink/Development/2.1/AdvancedJPA Queries
< EclipseLink | Development | 2.1
Revision as of 10:19, 19 January 2010 by Unnamed Poltroon (Talk) (→Fetch groups "Select emp(id, name) from Employee emp")
Contents
- 1 Extensions to be implemented - in priority order
- 1.1 All database functions
- 1.2 Spatial Functionality via JPQL
- 1.3 Functions in select and order by clause
- 1.4 Fields and tables, "from X x, Table(Y) y", "x.field(y)"
- 1.5 Object parameters and nested parameters "(:employee).id"
- 1.6 Dynamic FetchGroup in JPQL
- 1.7 SQL Hints
- 1.8 HIERARCHICAL QUERIES (Oracle)
- 1.9 Pessimistic locking "for update of emp"
- 1.10 Batch joins
- 2 Extensions already implemented in 2.0
Extensions to be implemented - in priority order
All database functions
JPQL equivalent to Oracle's NVL function
Spatial Functionality via JPQL
- PostGIS Intersects (forum)
- Oracle Spatial
- SDO_WITHIN_DISTANCE
- SDO_NN
- SDO_RELATE
- SDO_FILTER
Functions in select and order by clause
- ORDER BY RAND() - platform specific?
- Aggregate functions in ORDER BY
- Already works for select clause (tested ABS), doesn’t work for order by clause.
- However fails:
- SELECT CONCAT(e.firstName, e.lastName) FROM Employee e
- but works:
- SELECT CONCAT(e.firstName, e.lastName) FROM Employee e WHERE e.id > 0
Fields and tables, "from X x, Table(Y) y", "x.field(y)"
- ?
Object parameters and nested parameters "(:employee).id"
- Saw several times users attempting something like:
- SELECT e FROM Employee e WHERE e.address IN (SELECT a FROM Address…)
Dynamic FetchGroup in JPQL
This refers to specifying a dynamic FetchGroup that is used instead of the default one using JPQL.
Hint Example
Query query = em.createQuery("Select emp from Employee emp"); FetchGroup fg = new FetchGroup(); fg.addAttribute("name); query.setHint(QueryHints.FETCH_GROUP, fg); List<Employee> results = query.getResultsList();
Proposed JPQL:
Query query = em.createQuery("Select emp(name) from Employee emp"); List<Employee> results = query.getResultsList();
SQL Hints
Currently EclipseLink supports specifying (Oracle) SQL hints using [ DatabaseQuery.setHintString("...")] (see Using_Advanced_Query_API_(ELUG)#How_to_Use_Oracle_Hints) or through JPA using QueryHints.HINT. These hints are limited in where they can be generated in the resulting SQL.
These appear to be Oracle specific. Is this approach useful on other database platforms?
HIERARCHICAL QUERIES (Oracle)
- START WITH
- CONNECT BY
- ORDER SIBLINGS
Pessimistic locking "for update of emp"
- Accessible through hints ("for update" only).
Batch joins
- http://www.eclipse.org/forums/index.php?t=msg&th=123943&start=0&S=f9832b9dae179e13094b3c027540647f
- Accessible through hints.
Extensions already implemented in 2.0
Like with escapes, any types
- Works for strings:
- SELECT e FROM Employee e WHERE e.firstName LIKE "John"
- Have not tested for other types.
- Which types should be tested?
Nested fetch joins (both inner and outer)
- http://www.eclipse.org/forums/index.php?t=msg&goto=379275&#msg_379275
- http://www.eclipse.org/forums/index.php?&t=msg&th=125842
- Inner:
- SELECT p FROM SmallProject p JOIN p.teamLeader e JOIN e.address a WHERE p.name = 'Project1' or e.firstName = 'John' and a.province = 'ON'
- with setHint("eclipselink.join-fetch", "p.teamLeader.address")
- Outer:
- SELECT p FROM SmallProject p LEFT JOIN p.teamLeader e LEFT JOIN e.address a WHERE p.name = 'Project1' or e.firstName = 'John' and a.province = 'ON'
- with setHint("eclipselink.left-join-fetch", "p.teamLeader.address")
- Note that aliasing on the right side of FETCH is explicitly prohibited by the spec., so seems like no extension in JBQL is possible.
Pass list as parameter
- SELECT e FROM Employee e WHERE e.id in :list
- http://forums.oracle.com/forums/thread.jspa?threadID=871532