Perform additional retrieval of correct column names

Added a workaround for a MySQL bug #88718 introduced in the 8.0 series,
where the reflection of a foreign key constraint is not reporting the
correct case sensitivity for the referred column, leading to errors during
use of the reflected constraint such as when using the automap extension.
The workaround emits an additional query to the information_schema tables in
order to retrieve the correct case sensitive name.

Fixes: #4344
Change-Id: I08020d6eec43cbe8a56316660380d3739a0b45f7

diff --git a/doc/build/changelog/unreleased_12/4344.rst b/doc/build/changelog/unreleased_12/4344.rst
new file mode 100644 (file)
index 0000000..05be223
--- /dev/null
+++ b/doc/build/changelog/unreleased_12/4344.rst
@@ -0,0 +1,10 @@
+.. change::
+   :tags: bug, mysql
+   :tickets: 4344
+
+   Added a workaround for a MySQL bug #88718 introduced in the 8.0 series,
+   where the reflection of a foreign key constraint is not reporting the
+   correct case sensitivity for the referred column, leading to errors during
+   use of the reflected constraint such as when using the automap extension.
+   The workaround emits an additional query to the information_schema tables in
+   order to retrieve the correct case sensitive name.

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 45e8c251044800f08b8c2d5679e1791824b4c4f5..cd17bcdc48e488239fbbf6075354583b61371f05 100644 (file)
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -733,6 +733,7 @@ output::
 
 """
 
+from collections import defaultdict
 import re
 import sys
 import json
@@ -1979,6 +1980,10 @@ class MySQLDialect(default.DefaultDialect):
 
         default.DefaultDialect.initialize(self, connection)
 
+        self._needs_correct_for_88718 = (
+            not self._is_mariadb and self.server_version_info >= (8, )
+        )
+
         self._warn_for_known_db_issues()
 
     def _warn_for_known_db_issues(self):
@@ -2130,8 +2135,56 @@ class MySQLDialect(default.DefaultDialect):
                 'options': con_kw
             }
             fkeys.append(fkey_d)
+
+        if self._needs_correct_for_88718:
+            self._correct_for_mysql_bug_88718(fkeys, connection)
+
         return fkeys
 
+    def _correct_for_mysql_bug_88718(self, fkeys, connection):
+        # Foreign key is always in lower case (MySQL 8.0)
+        # https://bugs.mysql.com/bug.php?id=88718
+        # issue #4344 for SQLAlchemy
+
+        default_schema_name = connection.dialect.default_schema_name
+        col_tuples = [
+            (
+                rec['referred_schema'] or default_schema_name,
+                rec['referred_table'],
+                col_name
+            )
+            for rec in fkeys
+            for col_name in rec['referred_columns']
+        ]
+
+        if col_tuples:
+
+            correct_for_wrong_fk_case = connection.execute(
+                sql.text("""
+                    select table_schema, table_name, column_name
+                    from information_schema.columns
+                    where (table_schema, table_name, lower(column_name)) in
+                    :table_data;
+                """).bindparams(
+                    sql.bindparam("table_data", expanding=True)
+                ), table_data=col_tuples
+            )
+
+            d = defaultdict(dict)
+            for schema, tname, cname in correct_for_wrong_fk_case:
+                d[(schema, tname)][cname.lower()] = cname
+
+            for fkey in fkeys:
+                fkey['referred_columns'] = [
+                    d[
+                        (
+                            fkey['referred_schema'] or default_schema_name,
+                            fkey['referred_table']
+                        )
+                    ][col.lower()]
+                    for col in fkey['referred_columns']
+                ]
+
     @reflection.cache
     def get_check_constraints(
             self, connection, table_name, schema=None, **kw):

diff --git a/test/dialect/mysql/test_reflection.py b/test/dialect/mysql/test_reflection.py
index c244ba97274cb693caf7df36f4ae72285c29a5e0..c739d3c4f11245aab35d5f0489b0edcf97432c6c 100644 (file)
--- a/test/dialect/mysql/test_reflection.py
+++ b/test/dialect/mysql/test_reflection.py
@@ -4,7 +4,7 @@ from sqlalchemy.testing import eq_, is_
 from sqlalchemy import Column, Table, DDL, MetaData, TIMESTAMP, \
     DefaultClause, String, Integer, Text, UnicodeText, SmallInteger,\
     NCHAR, LargeBinary, DateTime, select, UniqueConstraint, Unicode,\
-    BigInteger, Index
+    BigInteger, Index, ForeignKey
 from sqlalchemy.schema import CreateIndex
 from sqlalchemy import event
 from sqlalchemy import sql
@@ -647,6 +647,50 @@ class ReflectionTest(fixtures.TestBase, AssertsCompiledSQL):
             [{'name': 'foo_idx', 'column_names': ['x'], 'unique': False}]
         )
 
+    @testing.provide_metadata
+    def test_case_sensitive_column_constraint_reflection(self):
+        # test for issue #4344 which works around
+        # MySQL 8.0 bug https://bugs.mysql.com/bug.php?id=88718
+
+        m1 = self.metadata
+
+        Table(
+            'Track', m1, Column('TrackID', Integer, primary_key=True)
+        )
+        Table(
+            'Track', m1, Column('TrackID', Integer, primary_key=True),
+            schema=testing.config.test_schema
+        )
+        Table(
+            'PlaylistTrack', m1, Column('id', Integer, primary_key=True),
+            Column('TrackID',
+                   ForeignKey('Track.TrackID', name='FK_PlaylistTrackId')),
+            Column(
+                'TTrackID',
+                ForeignKey(
+                    '%s.Track.TrackID' % (testing.config.test_schema,),
+                    name='FK_PlaylistTTrackId'
+                )
+            )
+        )
+        m1.create_all()
+
+        eq_(
+            inspect(testing.db).get_foreign_keys('PlaylistTrack'),
+            [
+                {'name': 'FK_PlaylistTTrackId',
+                 'constrained_columns': ['TTrackID'],
+                 'referred_schema': testing.config.test_schema,
+                 'referred_table': 'Track',
+                 'referred_columns': ['TrackID'], 'options': {}},
+                {'name': 'FK_PlaylistTrackId',
+                 'constrained_columns': ['TrackID'],
+                 'referred_schema': None,
+                 'referred_table': 'Track',
+                 'referred_columns': ['TrackID'], 'options': {}}
+            ]
+        )
+
 
 class RawReflectionTest(fixtures.TestBase):
     __backend__ = True