PeterVandivier
I have a document of the form…
Usinq jq, I would like to retrieve the object(s) from with the array a[] that have the exact value 2 for the nested attribute x.
In postgresql, it might look something like this:
<>https://dbfiddle.uk/?rdbms=postgres_13&fiddle=1f69408704bd95b38c55660c661529f6
I’ve been rubber-ducking my way through this post but it seems to be more about fuzzy matching text (not what I want) and filtering against an array with a pipe-into-contains() (vs filter against scalars in an unfolded array).
What syntax do I need to use to use to extract the full object {"b":{"x":2},"d":4} from the above document?
Top Answer
PeterVandivier
The select() function only ever evaluates a boolean. The bit that’s confusing from the array/contains() examples is the addition of the pipeline inside the select(). For exact equality. this is not necessary as select() can probe an arbitrary path into the object against which it evaluates in order complete it’s input expression.
In this case, the expression is .a[] | select(.b.x == 2)'
To compare back to our postgres example…
.a[] corresponds to jsonb_array_elements('{...}'::jsonb->'a')- the
| pipeline passes the objects from the left side through as individual tuples/rows
select() runs once-per-tuple and evaluates the expression inside ()
- a truthy evalution returns the whole tuple/object
.b.x is the probe obj->'b'->'x'== double equals is the necessary syntax.
HT to @jalkjaer who’s rubber ducked this before on gist
