So you put an escaped string into a JSON column...

#postgres #json #jsonb

Whoops! Let's pretend we made a mistake a while ago, and our application is writing escaped JSON strings into our Postgres JSON column instead of JSON objects. We can't use any JSON operators to select fields now! What are we to do?

select (ingredients #>> '{}')::jsonb->>'cheese' from pizza;

Do this ☝️. When you’ve got a table (pizza) with a jsonb column (ingredients), and you’ve accidentally put an escaped JSON string inside that column, instead of a JSON object. The value might look like this:

"{\"cheese\": \"mozzarella\"}"

See the quotes? That’s just a string at the root level inside of that JSON column. But what you really want looks like this:

{"cheese": "mozzarella"}

That’s better. But we’ve already made the mistake, so we’ve got to write a migration to fix the data. Here’s how we do it:

(ingredients #>> '{}')::jsonb

The #>> operator in Postgres gets a “JSON object at specified path as text” (PostgreSQL: Documentation: 9.3: JSON Functions and Operators). Here we’re passing in an empty path to say that we want Postgres to give us the unescaped string at the root level as a text value.

We can then cast that text value back to JSON like this: (stand-in-for-text-value)::jsonb. And then we have a normal, parsed JSON object at the root level that we can select fields off of.