SQL Error while trying to extract nested json data

Question

I am running an SQL query to extract nested JSON data.

SELECT watsonResponse.responseId,
       watsonResponse.chatId,
       d.*
FROM watson_response_table watsonResponse
         CROSS JOIN LATERAL (
    SELECT d2.*
    FROM jsonb_array_elements(watsonResponse.watsonresponse_output) AS d(events)
             CROSS JOIN LATERAL (
        SELECT d2.events ->> 'data'         AS watsonResponse_ouput_data
             , d2.events ->> 'text'         AS watsonResponse_output_text
             , d2.events ->> 'uiActionCode' AS watsonResponse_output_uiActionCode
        FROM jsonb_array_elements(d.events) AS d2(events)
        ) d2
    WHERE d.events ->> 'uiActionCode' = 'TextWithButton'
    ) d;

It fails with message SQL Error [22023]: ERROR: cannot extract elements from an object

I am using PostgresSQL 11+. Here is what the JSON looks like,

[
  {
    "text": [
      "Some text!"
    ],
    "uiActionCode": "textOnly"
  },
  {
    "data": {
      "type": "options",
      "options": [
        { "label": "test", "value": "testvalue" },
        { "label": "test2", "value": "testvalue2" },
        {
          "label": "test3",
          "value": "testQuestion?"
        }
      ]
    },
    "text": ["testQuestion2?"],
    "uiActionCode": "TextWithButton"
  }
]

Answer 1

If I am following this correctly, one level of unnesting is sufficient. You can then use the JSON accessors to get the results you want:

SELECT 
    r.responseId,
    r.chatId,
    d.events ->> 'uiActionCode' AS output_uiActionCode,
    d.events -> 'text' ->> 0    AS output_text,
    d.events -> 'data'          AS output_data,
FROM watson_response_table watsonResponse r
CROSS JOIN LATERAL jsonb_array_elements(r.watsonresponse_output) AS d(events)
WHERE d.events ->> 'uiActionCode' = 'TextWithButton'

Note that there is an important difference between accessors -> and ->> . The former returns an object, while the latter returns a text value. You need to carefully pick the correct operator according to what needs to be done for each field.