如何解析以下 JSON 字段？ (PostgreSQL)

Question

I seem to be unable to parse the following JSON field (named 'attributes') in the normal way:

select attributes -> 'foo' from schema.table

The JSON field has a key-date-value format I've never seen before.

In Postgres, how would I parse this JSON field to select just the value of the barcode? So far, I've had to fallback on string parsing instead, which is unideal.

[{"key": "amount", "date": "2019-08-01T13:39:50.823Z", "value": 10}, 
 {"key": "userId", "date": "2019-08-01T13:39:50.823Z", "value": 
  "4e79a15b24174970a913b5c94c030068"},
 {"key": "accountUuid", "date": "2019-08-01T13:39:50.823Z", "value": 
  "bd305700-b461-11e9-8153-adf1629b78f9"},
 {"key": "transactionId", "date": "2019-08-01T13:39:50.823Z", "value": 
  "e04a4099-8038-4cdc-8024-86147f23c749"},
 {"key": "paymentType", "date": "2019-08-01T13:39:50.823Z", "value": 
  "bank_transfer"},
 {"key": "vendor", "date": "2019-08-01T13:39:50.823Z", "value": 
  "12512"},
 {"key": "barcode", "date": "2019-08-01T13:39:50.823Z", "value": 
  "0298350928359829052"},
 {"key": "expirationDate", "date": "2019-08-01T13:39:50.823Z","value": 
  "2019-08-11T00:00:00.000Z"},
 {"key": "date", "date": "2019-08-01T13:39:50.823Z", "value":
  "2019-08-01T13:39:50.823Z"}]

Thanks a million!

Answer 1

You need to unnest the element of the array and then pick the one with the key = barcode :

select x.j ->> 'value'
from the_table
  cross join jsonb_array_elements(attributes) as x(j)
where x.j ->> 'key' = 'barcode'

If you are already using Postgres 12, this is a little bit easier as you can use a SQL/JSON path query

select jsonb_path_query_first(attributes, '$[*] ? (@.key == "barcode").value') 
from data