JPA query from java Object

Question

How can i use jpa for query over an object (not an entity)?

For example this simple code:

String [] theList = {a,b,c,d}. 
Query q = new Query("Select tl from theList tl")

Reason behind: the queries are dynamically created and executed, but the objects in the from clause of the jpql query aren't necessarily mapped tables. In some cases there are just an Object, So the actual behavior needed is modify the query during execution of the program to meet the criteria, but i don't know how to modify the query.

Edit: I Don't use native queries because of portability of code. It will be the last option.

Thanks for suggestion. I have edited the Question. The reason is that behind the project there are several dbms (Oracle, Sybase, SqlServer and Postgres) and there are over 10000 queries, so much to maintain with Database-specifics, +1 for the suggest. — Cesar Leonardo Ochoa Contreras
– Cesar Leonardo Ochoa Contreras, Commented Feb 27, 2019 at 19:56
Sorry but can you put much details I don't get your question, what did you mean by but the objects in the from clause of the jpql query aren't necessarily mapped tables — Youcef LAIDANI
– Youcef LAIDANI, Commented Feb 27, 2019 at 20:03
You mean query in memory, or query in database (in which case you are not querying over an "object") ? — user3973283
– user3973283, Commented Feb 28, 2019 at 7:04
@YCF_L Literaly the expression. The Objects of the from clause of the query aren't mapped tables in some cases, but java objects. — Cesar Leonardo Ochoa Contreras
– Cesar Leonardo Ochoa Contreras, Commented Feb 28, 2019 at 15:26

LppEdd · Accepted Answer · 2019-02-28 14:18:26Z

1

What you're looking for is called LINQ, and unfortunately (?) it is available only in C#.

However, you can partially emulate it with Stream(s).
A Stream offers basically all the operators you need

.filter()               where
.max()                  max
.sorted()               orderby
.limit()                limit
.skip()                 offset
.collect(groupingBy())  group by

And so on. Just give a look at the Javadoc!

edited Feb 28, 2019 at 14:18

answered Feb 27, 2019 at 19:54

LppEdd

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4 Comments

Cesar Leonardo Ochoa Contreras Over a year ago

I'll take a look, +1 for the suggestion. Actually i'm reading about eclipselink expressions but i'm unsure on how to do it.

LppEdd Over a year ago

@CesarLeonardoOchoaContreras but wait. The example shows an array you're operating on. Eclipselink expressions are for database accesses.

Cesar Leonardo Ochoa Contreras Over a year ago

Oh yeah. This is because i'm dealing with distincts levels of subqueries (Remeber that jpa don't support subqueries in the FROM Clause, so i'm extracting and executing the subqueries to objects first and my purpose is to query then those objects.

LppEdd Over a year ago

@CesarLeonardoOchoaContreras Well, once you have your first result-set from JPA, if you don't need the latest data (which might be updated by other users in the database) you can operate via Streams.

Akash Chandwani · Accepted Answer · 2019-02-27 20:33:48Z

0

I think 'JdbcTemplate' would suffice your requirement.

JdbcTemplate gives you the flexibility to run native queries and map them to a Java class.

However, you'll have to explicitly map your Java class with the column names in the database.

edited Feb 27, 2019 at 20:33

answered Feb 27, 2019 at 20:22

Akash Chandwani

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Cesar Leonardo Ochoa Contreras · Accepted Answer · 2019-03-05 20:25:57Z

0

I have solved using joSQL. Is a powerfull opensource tool that allows you to query over java objects using "sql". It is not jpa but satisfied my needs. Another tool i have seen that do that is called querydsl.

answered Mar 5, 2019 at 20:25

Cesar Leonardo Ochoa Contreras

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