Fixed #12990, Refs #27694 -- Added JSONField model field.

Thanks to Adam Johnson, Carlton Gibson, Mariusz Felisiak, and Raphael
Michel for mentoring this Google Summer of Code 2019 project and
everyone else who helped with the patch.

Special thanks to Mads Jensen, Nick Pope, and Simon Charette for
extensive reviews.

Co-authored-by: Mariusz Felisiak <felisiak.mariusz@gmail.com>

1 files changed, 20 insertions, 1 deletions

diff --git a/django/db/backends/mysql/introspection.py b/django/db/backends/mysql/introspection.py
index 50160ba590..1a104c7810 100644
--- a/django/db/backends/mysql/introspection.py
+++ b/django/db/backends/mysql/introspection.py
@@ -9,7 +9,7 @@ from django.db.backends.base.introspection import (
 from django.db.models import Index
 from django.utils.datastructures import OrderedSet
 
-FieldInfo = namedtuple('FieldInfo', BaseFieldInfo._fields + ('extra', 'is_unsigned'))
+FieldInfo = namedtuple('FieldInfo', BaseFieldInfo._fields + ('extra', 'is_unsigned', 'has_json_constraint'))
 InfoLine = namedtuple('InfoLine', 'col_name data_type max_len num_prec num_scale extra column_default is_unsigned')
 
 
@@ -24,6 +24,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         FIELD_TYPE.DOUBLE: 'FloatField',
         FIELD_TYPE.FLOAT: 'FloatField',
         FIELD_TYPE.INT24: 'IntegerField',
+        FIELD_TYPE.JSON: 'JSONField',
         FIELD_TYPE.LONG: 'IntegerField',
         FIELD_TYPE.LONGLONG: 'BigIntegerField',
         FIELD_TYPE.SHORT: 'SmallIntegerField',
@@ -53,6 +54,10 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                 return 'PositiveIntegerField'
             elif field_type == 'SmallIntegerField':
                 return 'PositiveSmallIntegerField'
+        # JSON data type is an alias for LONGTEXT in MariaDB, use check
+        # constraints clauses to introspect JSONField.
+        if description.has_json_constraint:
+            return 'JSONField'
         return field_type
 
     def get_table_list(self, cursor):
@@ -66,6 +71,19 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         Return a description of the table with the DB-API cursor.description
         interface."
         """
+        json_constraints = {}
+        if self.connection.mysql_is_mariadb and self.connection.features.can_introspect_json_field:
+            # JSON data type is an alias for LONGTEXT in MariaDB, select
+            # JSON_VALID() constraints to introspect JSONField.
+            cursor.execute("""
+                SELECT c.constraint_name AS column_name
+                FROM information_schema.check_constraints AS c
+                WHERE
+                    c.table_name = %s AND
+                    LOWER(c.check_clause) = 'json_valid(`' + LOWER(c.constraint_name) + '`)' AND
+                    c.constraint_schema = DATABASE()
+            """, [table_name])
+            json_constraints = {row[0] for row in cursor.fetchall()}
         # information_schema database gives more accurate results for some figures:
         # - varchar length returned by cursor.description is an internal length,
         #   not visible length (#5725)
@@ -100,6 +118,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                 info.column_default,
                 info.extra,
                 info.is_unsigned,
+                line[0] in json_constraints,
             ))
         return fields