Extract and cast values from a `TextField` or `JSONField` (in Django)

json_extract_and_cast.py

from django.db.models import CharField
from django.db.models import Func
from django.db.models import Value
from django.db.models.functions import Cast


class JSONExtractAndCast(Cast):
    def __init__(self, expression, *paths, output_field):
        # borrowed from django_mysql.models.functions.JSONExtract
        exprs = [expression]
        for path in paths:
            if not hasattr(path, "resolve_expression"):
                path = Value(path)
            exprs.append(path)

        extracted_value = Func(
            *exprs,
            function="JSON_EXTRACT",
            output_field=CharField(),
        )
        unquoted_value = Func(
            extracted_value,
            function="JSON_UNQUOTE",
            output_field=output_field,
        )
        super().__init__(unquoted_value, output_field=output_field)