Saturday, March 2, 2024

Projecting Kind Protected Nested TableRecords with jOOQ 3.17 – Java, SQL and jOOQ.


A protracted standing function request has seen little love from the jOOQ group, regardless of lots of people in all probability wanting it. It goes by the unimpressive title Let Desk<R> prolong SelectField<R>: https://github.com/jOOQ/jOOQ/points/4727

What does the function imply, particularly?

The superior PostgreSQL

Let’s take a look at a very cool PostgreSQL function. In PostgreSQL, it’s potential to nest data in numerous methods, together with by merely referencing (unqualified) desk names within the SELECT clause. Utilizing the sakila database, that is legitimate PostgreSQL:

SELECT DISTINCT actor, class
FROM actor
JOIN film_actor USING (actor_id)
JOIN film_category USING (film_id)
JOIN class USING (category_id)

This lists all actors and the classes of movies they performed in. There’s solely actually one factor this might imply, proper? It appears to be like as if it was syntax sugar for this, which works on all database merchandise:

SELECT DISTINCT actor.*, class.*
FROM actor
JOIN film_actor USING (actor_id)
JOIN film_category USING (film_id)
JOIN class USING (category_id)

Nevertheless it’s subtly totally different. The consequence appears to be like one thing like this, in psql:

                      actor                      |               class
-------------------------------------------------+---------------------------------------
...                                              |
 (1,PENELOPE,GUINESS,"2006-02-15 04:34:33")      | (12,Music,"2006-02-15 04:46:27")
 (1,PENELOPE,GUINESS,"2006-02-15 04:34:33")      | (13,New,"2006-02-15 04:46:27")
 (1,PENELOPE,GUINESS,"2006-02-15 04:34:33")      | (14,Sci-Fi,"2006-02-15 04:46:27")
 (1,PENELOPE,GUINESS,"2006-02-15 04:34:33")      | (15,Sports activities,"2006-02-15 04:46:27")
 (2,NICK,WAHLBERG,"2006-02-15 04:34:33")         | (1,Motion,"2006-02-15 04:46:27")
 (2,NICK,WAHLBERG,"2006-02-15 04:34:33")         | (2,Animation,"2006-02-15 04:46:27")
...                                              |

For those who’re utilizing DBeaver to show the outcomes, you’ll see an identical nesting construction:

What occurred right here is that PostgreSQL merely nested the 2 tables as nested data within the output. The illustration is a bit totally different from projecting the asterisks (*), nevertheless it’s logically the identical factor (with just a few refined variations). Isn’t that cool? A few of you is perhaps used to utilizing the ROW constructor like this (the place the ROW key phrase is optionally available):

SELECT DISTINCT 
  ROW(actor_id, first_name, last_name) AS actor, 
  ROW(category_id, title) AS class
FROM actor
JOIN film_actor USING (actor_id)
JOIN film_category USING (film_id)
JOIN class USING (category_id)

This additionally produces nested data, although this time with out a report sort. From psql:

           actor           |    class
---------------------------+-----------------
 ...                       |
 (1,PENELOPE,GUINESS)      | (12,Music)
 (1,PENELOPE,GUINESS)      | (13,New)
 (1,PENELOPE,GUINESS)      | (14,Sci-Fi)
 (1,PENELOPE,GUINESS)      | (15,Sports activities)
 (2,NICK,WAHLBERG)         | (1,Motion)
 (2,NICK,WAHLBERG)         | (2,Animation)
 (2,NICK,WAHLBERG)         | (3,Kids)
 (2,NICK,WAHLBERG)         | (4,Classics)

Or, from DBeaver:

Can this be utilized in jOOQ?

Whereas Oracle/PostgreSQL UDTs have at all times been accessible, such ad-hoc nested report expressions projected from the SELECT clause have been potential in jOOQ since jOOQ 3.15. Similar to the superior MULTISET operator, they’re key to accessing extra highly effective nested assortment mappings.

However ranging from jOOQ 3.17, the desk expression model is now lastly additionally accessible. The earlier SQL queries from PostgreSQL would translate to this, in jOOQ:

// Projecting desk expressions
Outcome<Record2<ActorRecord, CategoryRecord>> result1 =
ctx.selectDistinct(ACTOR, CATEGORY)
   .from(ACTOR)
   .be a part of(FILM_ACTOR).utilizing(FILM_ACTOR.ACTOR_ID)
   .be a part of(FILM_CATEGORY).utilizing(FILM_CATEGORY.FILM_ID)
   .be a part of(CATEGORY).utilizing(CATEGORY.CATEGORY_ID)
   .fetch();

// Projecting ad-hoc ROW expressions
Outcome<Record2<
    Record3<Lengthy, String, String>, // actor
    Record2<Lengthy, String> // class
>> result2 =
ctx.selectDistinct(
       row(
           ACTOR.ACTOR_ID, 
           ACTOR.FIRST_NAME, 
           ACTOR.LAST_NAME
       ).as("actor"),
       row(CATEGORY.CATEGORY_ID, CATEGORY.NAME).as("class")
   )
   .from(ACTOR)
   .be a part of(FILM_ACTOR).utilizing(FILM_ACTOR.ACTOR_ID)
   .be a part of(FILM_CATEGORY).utilizing(FILM_CATEGORY.FILM_ID)
   .be a part of(CATEGORY).utilizing(CATEGORY.CATEGORY_ID)
   .fetch();

Similar to with jOOQ 3.15, you can even ad-hoc converters to transform the jOOQ-generated report to something extra helpful to your goal customers, e.g. a Java 16 report sort.

Combining this with implicit joins

A really highly effective function in jOOQ are implicit joins, which have been added in jOOQ 3.11. Possibly, you don’t discover the specific be a part of syntax very pleasing to jot down on a regular basis? Why not write issues like this, as a substitute:

Outcome<Record2<CustomerRecord, CountryRecord>> consequence =
ctx.choose(
       CUSTOMER,
       CUSTOMER.deal with().metropolis().nation()
   )
   .from(CUSTOMER)
   .fetch();

Notice that once more, we don’t challenge any particular person columns of the CUSTOMER or COUNTRY desk, we simply challenge all the desk, similar to in PostgreSQL, and all sort protected with getters and setters accessible on the ensuing data.

Caveat

As at all times, know what you’re doing, and why you’re doing it. Each in PostgreSQL and in jOOQ, projecting the CUSTOMER desk is usually simply sugar for projecting CUSTOMER.*, i.e. you would possibly get numerous information that you simply may not want. There’s at all times a comfort / efficiency tradeoff to be made. Ideally, if you wish to make use of this strategy lots, create views in your database, and generate jOOQ code for these views. With artificial international keys in jOOQ, you may nonetheless revenue from the implicit be a part of syntax on views as nicely.

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