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Re: [dali-dev] JPQL query generation?
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Hi Tom,
There isn't a visual query builder in Dali but JPQL support is on the
feature backlog.
I really wouldn't recommend SQL queries. They're there as a last
resort. You lose a number of advantages of JPA including encapsulation
of the data model. You'll be coupling your code (queries) to the data
model. Coupling should be limited to your mappings. Mappings can adapt
to data model changes (and Dali will detect them), and your queries can
continue to work without change since you're querying on the object
model. Also, JPA persistence providers parse JPQL and can do things
like avoid database round trips by using a cache. A primary key query
is an obvious one. If what you want is in the cache and you know it's
reliable why go to the database? When using SQL your provider will just
pass it along and process the results so you lower the value of the
cache. The big issue IMHO is the unnecessary coupling of queries to the
data model and the brittleness it introduces. I've seen database
migrations from DB/2 to Oracle of two applications in a workflow, one
using TopLink, one using direct SQL. The SQL based application was way
more expensive to port. They had to go over every line of SQL whereas
the TopLink based application required the mappings adjusted (minimally
I might add) and the application ran. Theory is nice but seeing it play
out in real life made the advantage of object based queries concrete.
Shaun
Tom Mutdosch wrote:
Hi all,
Is there any way to assist in generating queries (using Java
Persistence Query Language) in Dali? For example, is there any visual
query builder that can generate a JPQL query? I know the Data Tools
Platform provides a visual SQL Builder. It might be nice if there was
something similar that Dali could use. For example, someone who
doesn't know much SQL but wants to "retrieve all Departments
containing Employees with at least 5 years of experience". I know
that JPA can also be used with SQL Queries, so maybe that would be the
recommended advice for such a user - to use the SQL Query Builder and
then supply that query to the EntityManager. How hard would it be for
Dali to reuse the SQL Builder to have it generate JPQL instead?
Thanks
Tom
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--
Shaun Smith
Principal Product Manager
Oracle TopLink
shaun.smith@xxxxxxxxxx
