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

1 files changed, 53 insertions, 0 deletions

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 45e8c2510..cd17bcdc4 100644
--- 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):