Jooq ArrayAgg#isNull not working as expected - sql

Question

I have a project which uses jooq + postgres with multiple tables and relations between them.
while I was creating a select query with jooq I had to use arrayAgg for my specific scenario.
dslContext.select(arrayAgg(tableName.INTEGER_LETS_SAY).as("static_name")
the specific column INTEGER_LETS_SAY is nullable.
when the results passed in arrayAgg are all null then the response of the postgres is '{null}' ( tested with getQuery().getSql() ) but the where statement cannot return true for all the methods I tried.
for example :
field("static_name", Long[].class).isNull()
field("static_name", Long[].class).equal(new Long[] {null})
field("static_name", Long[].class).equal(DSL.castNull(Long[].class)
field("static_name", Long[].class).cast(String.class).eq(DSL.value("{null}")))
field("static_name", Long[].class).cast(String.class).eq(DSL.value("'{null}'")))
any clue what am I doing wrong?
Note : I did try the query with plain sql and static_name = '{null}' worked

Answer 1

{NULL} is PostgreSQL's text representation of an array containing one SQL NULL value. You can try it like this:
select (array[null]::int[])::text ilike '{null}' as a
It yields:
a |
----|
true|
Note, I'm using ilike for case insensitive comparison. On my installation, I'm getting {NULL}, not {null}. If you wanted to compare things as text, you could do it using Field.likeIgnoreCase(). E.g. this works for me:
System.out.println(ctx.select(
field(val(new Long[] { null }).cast(String.class).likeIgnoreCase("{null}")).as("a")
).fetch());
Producing:
+----+
|a |
+----+
|true|
+----+
But much better, do not work with the text representation. Instead, follow this suggestion here. In SQL:
select true = all(select a is null from unnest(array[null]::int[]) t (a)) as a
In jOOQ:
System.out.println(ctx.select(
field(inline(true).eq(all(
select(field(field(name("a")).isNull()))
.from(unnest(val(new Long[] { null })).as("t", "a"))
))).as("a")
).fetch());
It gets a bit verbose because of all the wrapping Condition in Field<Boolean> using DSL.field(Condition).
Alternatively, use e.g. NUM_NONNULLS() (Credits to Vik Fearing for this appraoch):
System.out.println(ctx.select(
field("num_nonnulls(variadic {0})", INTEGER, val(new Long { null }))
).fetch());