Remove several elements from Postgres array with jOOQ - postgresql

Question

I'm trying to use jOOQ to create a function akin to arrayRemove but that allows removing several elements at once from a PostgreSQL column of type uuid[].
So my first attempt was:
private Field<UUID[]> arrayRemoveAll(final Field<UUID[]> field, final Set<UUID> elements) {
return select(field("array_agg(tab.col)", UUID[].class))
.from(unnest(field).as("tab", "col"))
.where(field("tab.col", UUID.class).notIn(elements))
.asField();
}
Which succeeds at removing every requested element, but has the problem of returning null instead of an empty array if I attempt to remove every element.
So I added a coalesce to my code to make it return an empty array:
private Field<UUID[]> arrayRemoveAll(final Field<UUID[]> field, final Set<UUID> elements) {
final Field<UUID[]> newArray = select(field("array_agg(tab.col)", UUID[].class))
.from(unnest(field).as("tab", "col"))
.where(field("tab.col", UUID.class).notIn(elements))
.asField();
return coalesce(newArray, field("{}", UUID[].class));
}
But running this code threw this exception:
org.jooq.exception.DataAccessException: SQL [<<confidential SQL removed>>]
Caused by: org.postgresql.util.PSQLException: ERROR: syntax error at or near ")"
This is the part of the SQL exception it is complaining about (notice the trailing comma and missing 2nd parameter in the coalesce):
coalesce((select array_agg(tab.col)
from unnest("my_schema"."my_table"."my_field") as "tab"("col")
where tab.col not in (?, ?)), )
Is this a bug in jOOQ?

Answer 1

I found that I had a mix of field and val in the code above, changing field("{}", UUID[].class) to val(new UUID[0]) solves the problem.
Also check Lukas Eder's answer about how to solve the issue using field.
So the final code, with generics, looks like this:
private <T> Field<T[]> arrayRemoveAll(final Field<T[]> field, final Set<T> elements, final T[] emptyArray) {
final Field<T[]> newArray = select(field("array_agg(tab.col)"))
.from(unnest(field).as("tab", "col"))
.where(field("tab.col").notIn(elements))
.asField();
return coalesce(newArray, val(emptyArray));
}
And you can use it in your statements like this:
using(configuration)
.update(MY_TABLE)
.set(MY_TABLE.MY_COLUMN,
arrayRemoveAll(MY_TABLE.MY_COLUMN, someElements, new UUID[0]))
.where(MY_TABLE.ID.eq(...))
.execute();

Answer 2

Your field("{}") does not generate the {} string in the SQL, but is considered a part of jOOQ's plain SQL templating language, which unfortunately doesn't allow for escaping those braces:
https://www.jooq.org/doc/latest/manual/sql-building/plain-sql-templating
Luckily, PostgreSQL supports a more formal, standards-compliant way to create an empty array literal:
field("array[]::uuid[]", UUID.class)