From b2aad9ad4d35ee3bb448ba698b8c56bb972bdd8a Mon Sep 17 00:00:00 2001
From: Hasan Ramezani <hasan.r67@gmail.com>
Date: Tue, 30 Jul 2019 15:18:12 +0200
Subject: [PATCH] Refs #30593 -- Added _parse_constraint_columns() hook to
 introspection on MariaDB.

---
 django/db/backends/mysql/introspection.py  | 17 ++++++++++-------
 tests/backends/mysql/test_introspection.py | 22 ++++++++++++++++++++++
 2 files changed, 32 insertions(+), 7 deletions(-)
 create mode 100644 tests/backends/mysql/test_introspection.py

diff --git a/django/db/backends/mysql/introspection.py b/django/db/backends/mysql/introspection.py
index a64e82e004..86133a254e 100644
--- a/django/db/backends/mysql/introspection.py
+++ b/django/db/backends/mysql/introspection.py
@@ -147,6 +147,15 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
             return self.connection.features._mysql_storage_engine
         return result[0]
 
+    def _parse_constraint_columns(self, check_clause):
+        check_columns = OrderedSet()
+        statement = sqlparse.parse(check_clause)[0]
+        tokens = (token for token in statement.flatten() if not token.is_whitespace)
+        for token in tokens:
+            if token.ttype in [sqlparse.tokens.Name, sqlparse.tokens.Literal.String.Single]:
+                check_columns.add(token.value[1:-1])
+        return check_columns
+
     def get_constraints(self, cursor, table_name):
         """
         Retrieve any constraints or keys (unique, pk, fk, check, index) across
@@ -201,14 +210,8 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
             """
             cursor.execute(type_query, [table_name])
             for constraint, check_clause in cursor.fetchall():
-                # Parse columns.
-                columns = OrderedSet()
-                for statement in sqlparse.parse(check_clause):
-                    for token in statement.flatten():
-                        if token.ttype in [sqlparse.tokens.Name, sqlparse.tokens.Literal.String.Single]:
-                            columns.add(token.value[1:-1])
                 constraints[constraint] = {
-                    'columns': columns,
+                    'columns': self._parse_constraint_columns(check_clause),
                     'primary_key': False,
                     'unique': False,
                     'index': False,
diff --git a/tests/backends/mysql/test_introspection.py b/tests/backends/mysql/test_introspection.py
new file mode 100644
index 0000000000..1b8fb94ed9
--- /dev/null
+++ b/tests/backends/mysql/test_introspection.py
@@ -0,0 +1,22 @@
+from unittest import skipUnless
+
+from django.db import connection
+from django.test import TestCase
+
+
+@skipUnless(connection.vendor == 'mysql', 'MySQL tests')
+class ParsingTests(TestCase):
+    def test_parse_constraint_columns(self):
+        tests = (
+            ('`height` >= 0', ['height']),
+            ('`cost` BETWEEN 1 AND 10', ['cost']),
+            ('`ref1` > `ref2`', ['ref1', 'ref2']),
+            (
+                '`start` IS NULL OR `end` IS NULL OR `start` < `end`',
+                ['start', 'end'],
+            ),
+        )
+        for check_clause, expected_columns in tests:
+            with self.subTest(check_clause):
+                check_columns = connection.introspection._parse_constraint_columns(check_clause)
+                self.assertEqual(list(check_columns), expected_columns)