Allow metadata.reflect() to recover from unreflectable tables

Added support for views that are unreflectable due to stale
table definitions, when calling :meth:`.MetaData.reflect`; a warning
is emitted for the table that cannot respond to ``DESCRIBE``
but the operation succeeds.  The MySQL dialect now
raises UnreflectableTableError which is in turn caught by
MetaData.reflect().  Reflecting the view standalone raises
this error directly.

Change-Id: Id8005219d8e073c154cc84a873df911b4a6cf4d6
Fixes: #3871

4 files changed, 30 insertions, 7 deletions

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 21d325d0c..277ae5815 100644
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -2052,8 +2052,14 @@ class MySQLDialect(default.DefaultDialect):
                 rp = connection.execution_options(
                     skip_user_error_events=True).execute(st)
             except exc.DBAPIError as e:
-                if self._extract_error_code(e.orig) == 1146:
+                code = self._extract_error_code(e.orig)
+                if code == 1146:
                     raise exc.NoSuchTableError(full_name)
+                elif code == 1356:
+                    raise exc.UnreflectableTableError(
+                        "Table or view named %s could not be "
+                        "reflected: %s" % (full_name, e)
+                    )
                 else:
                     raise
             rows = self._compat_fetchall(rp, charset=charset)
@@ -2063,7 +2069,6 @@ class MySQLDialect(default.DefaultDialect):
         return rows
 
 
-
 class _DecodingRowProxy(object):
     """Return unicode-decoded values based on type inspection.
 
diff --git a/lib/sqlalchemy/exc.py b/lib/sqlalchemy/exc.py
index e8ba34ba4..3db3c1085 100644
--- a/lib/sqlalchemy/exc.py
+++ b/lib/sqlalchemy/exc.py
@@ -199,6 +199,14 @@ class NoSuchTableError(InvalidRequestError):
     """Table does not exist or is not visible to a connection."""
 
 
+class UnreflectableTableError(InvalidRequestError):
+    """Table exists but can't be reflectted for some reason.
+
+    .. versionadded:: 1.2
+
+    """
+
+
 class UnboundExecutionError(InvalidRequestError):
     """SQL was attempted without a database connection to execute it on."""
 
diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index 1cdc7b425..a9aee5883 100644
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -3903,7 +3903,10 @@ class MetaData(SchemaItem):
                         name not in current]
 
             for name in load:
-                Table(name, self, **reflect_opts)
+                try:
+                    Table(name, self, **reflect_opts)
+                except exc.UnreflectableTableError as uerr:
+                    util.warn("Skipping table %s: %s" % (name, uerr))
 
     def append_ddl_listener(self, event_name, listener):
         """Append a DDL event listener to this ``MetaData``.
diff --git a/lib/sqlalchemy/testing/assertions.py b/lib/sqlalchemy/testing/assertions.py
index 884556345..dfea33dc7 100644
--- a/lib/sqlalchemy/testing/assertions.py
+++ b/lib/sqlalchemy/testing/assertions.py
@@ -130,9 +130,16 @@ def _expect_warnings(exc_cls, messages, regex=True, assert_=True,
 
     real_warn = warnings.warn
 
-    def our_warn(msg, exception, *arg, **kw):
-        if not issubclass(exception, exc_cls):
-            return real_warn(msg, exception, *arg, **kw)
+    def our_warn(msg, *arg, **kw):
+        if isinstance(msg, exc_cls):
+            exception = msg
+            msg = str(exception)
+        elif arg:
+            exception = arg[0]
+        else:
+            exception = None
+        if not exception or not issubclass(exception, exc_cls):
+            return real_warn(msg, *arg, **kw)
 
         if not filters:
             return
@@ -143,7 +150,7 @@ def _expect_warnings(exc_cls, messages, regex=True, assert_=True,
                 seen.discard(filter_)
                 break
         else:
-            real_warn(msg, exception, *arg, **kw)
+            real_warn(msg, *arg, **kw)
 
     with mock.patch("warnings.warn", our_warn):
         yield