Postgres JSONB Editing columns - postgresql

Question

I was going through the Postgres Jsonb documentation but was unable to find a solution for a small issue I'm having.
I've got a table : MY_TABLE
that has the following columns:
User, Name, Data and Purchased
One thing to note is that "Data" is a jsonb and has multiple fields. One of the fields inside of "Data" is "Attribute" but the values it can hold are not in sync. What I mean is, it could be a string, a list of strings, an empty list, or just an empty string. However, I want to change this.
The only values that I want to allow are a list of strings and an empty list. I want to convert all the empty strings to empty lists and regular strings to a list of strings.
I have tried using json_build_array but have not had any luck
So for example, I'd want my final jsonb to look like :
[{
"Id": 1,
"Attributes": ["Test"]
},
{
"Id": 2,
"Attributes": []
},
{
"Id": 3,
"Attributes": []
}]
when converted from
{
"Id": 1,
"Attributes": "Test"
},
{
"Id": 2,
"Attributes": ""
},
{
"Id": 3,
"Attributes": []
}
]
I only care about the "Attributes" field inside of the Json, not any other fields.
I also want to ensure for some Attributes that have an empty string "Attributes": "", they get mapped to an empty list and not a list with an empty string ([] not [""])
I also want to preserve the empty array values ([]) for the Attributes that already hold an empty array value.
This is what I have so far:
jsonb_set(
mycol,
'{Attributes}',
case when js ->> 'Attributes' <> ''
then jsonb_build_array(js ->> 'Attributes')
else '[]'::jsonb
end
)
However, Attributes: [] is getting mapped to ["[]"]

Answer 1

Use jsonb_array_elements() to iterate over the elements of each 'data' cell and jsonb_agg to regroup the transform values together into an array:
WITH test_data(js) AS (
VALUES ($$ [
{
"Id": 1,
"Attributes": "Test"
},
{
"Id": 2,
"Attributes": ""
},
{
"Id": 3,
"Attributes": []
}
]
$$::JSONB)
)
SELECT transformed_elem
FROM test_data
JOIN LATERAL (
SELECT jsonb_agg(jsonb_set(
elem,
'{Attributes}',
CASE
WHEN elem -> 'Attributes' IN ('""', '[]') THEN '[]'::JSONB
WHEN jsonb_typeof(elem -> 'Attributes') = 'string' THEN jsonb_build_array(elem -> 'Attributes')
ELSE elem -> 'Attributes'
END
)) AS transformed_elem
FROM jsonb_array_elements(test_data.js) AS f(elem) -- iterate over every element in the array
) s
ON TRUE
returns
[{"Id": 1, "Attributes": ["Test"]}, {"Id": 2, "Attributes": []}, {"Id": 3, "Attributes": []}]