Fixed #28804 -- Fixed "Unknown system variable 'transaction_isolation'" on MariaDB.

Regression in 967450a3.

django/db/backends/mysql/base.py

@@ -221,9 +221,6 @@ class DatabaseWrapper(BaseDatabaseWrapper):
                         isolation_level,
                         ', '.join("'%s'" % s for s in sorted(self.isolation_levels))
                     ))
-            # The variable assignment form of setting transaction isolation
-            # levels will be used, e.g. "set transaction_isolation='repeatable-read'".
-            isolation_level = isolation_level.replace(' ', '-')
         self.isolation_level = isolation_level
         kwargs.update(options)
         return kwargs
@@ -231,10 +228,6 @@ class DatabaseWrapper(BaseDatabaseWrapper):
     def get_new_connection(self, conn_params):
         return Database.connect(**conn_params)
 
-    @cached_property
-    def transaction_isolation_variable(self):
-        return 'tx_isolation' if self.mysql_version < (5, 7, 20) else 'transaction_isolation'
-
     def init_connection_state(self):
         assignments = []
         if self.features.is_sql_auto_is_null_enabled:
@@ -242,14 +235,14 @@ class DatabaseWrapper(BaseDatabaseWrapper):
             # a recently inserted row will return when the field is tested
             # for NULL. Disabling this brings this aspect of MySQL in line
             # with SQL standards.
-            assignments.append('SQL_AUTO_IS_NULL = 0')
+            assignments.append('SET SQL_AUTO_IS_NULL = 0')
 
         if self.isolation_level:
-            assignments.append("%s = '%s'" % (self.transaction_isolation_variable, self.isolation_level))
+            assignments.append('SET SESSION TRANSACTION ISOLATION LEVEL %s' % self.isolation_level.upper())
 
         if assignments:
             with self.cursor() as cursor:
-                cursor.execute('SET ' + ', '.join(assignments))
+                cursor.execute('; '.join(assignments))
 
     def create_cursor(self, name=None):
         cursor = self.connection.cursor()

tests/backends/mysql/tests.py

@@ -20,7 +20,7 @@ class IsolationLevelTests(TestCase):
     read_committed = 'read committed'
     repeatable_read = 'repeatable read'
     isolation_values = {
-        level: level.replace(' ', '-').upper()
+        level: level.upper()
         for level in (read_committed, repeatable_read)
     }
 
@@ -38,8 +38,8 @@ class IsolationLevelTests(TestCase):
     @staticmethod
     def get_isolation_level(connection):
         with connection.cursor() as cursor:
-            cursor.execute("SELECT @@session.%s" % connection.transaction_isolation_variable)
-            return cursor.fetchone()[0]
+            cursor.execute("SHOW VARIABLES WHERE variable_name IN ('transaction_isolation', 'tx_isolation')")
+            return cursor.fetchone()[1].replace('-', ' ')
 
     def test_auto_is_null_auto_config(self):
         query = 'set sql_auto_is_null = 0'