Fix Connection.description migration for MySQL8

Due to not executing MySQL8 tests Fixed in apache#12591 added
description for connection table was not compatible with
MySQL8 with utf8mb4 character set.

This change adds migration and fixes the previous migration
to make it compatible.

airflow/migrations/versions/61ec73d9401f_add_description_field_to_connection.py

@@ -36,8 +36,16 @@
 
 def upgrade():
     """Apply Add description field to connection"""
+    conn = op.get_bind()  # pylint: disable=no-member
+
     with op.batch_alter_table('connection') as batch_op:
-        batch_op.add_column(sa.Column('description', sa.String(length=5000), nullable=True))
+        if conn.dialect.name == "mysql":
+            # Handles case where on mysql with utf8mb4 this would exceed the size of row
+            # We have to set text type in this migration even if originally it was string
+            # This is permanently fixed in the follow-up migration 64a7d6477aae
+            batch_op.add_column(sa.Column('description', sa.Text(length=5000), nullable=True))
+        else:
+            batch_op.add_column(sa.Column('description', sa.String(length=5000), nullable=True))
 
 
 def downgrade():

airflow/migrations/versions/64a7d6477aae_fix_description_field_in_connection_to_.py

@@ -0,0 +1,78 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+"""fix description field in connection to be text
+
+Revision ID: 64a7d6477aae
+Revises: f5b5ec089444
+Create Date: 2020-11-25 08:56:11.866607
+
+"""
+
+import sqlalchemy as sa  # noqa
+from alembic import op  # noqa
+
+# revision identifiers, used by Alembic.
+revision = '64a7d6477aae'
+down_revision = '61ec73d9401f'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    """Apply fix description field in connection to be text"""
+    conn = op.get_bind()  # pylint: disable=no-member
+    if conn.dialect.name == "sqlite":
+        # in sqlite TEXT and STRING column types are the same
+        return
+    if conn.dialect.name == "mysql":
+        op.alter_column(
+            'connection',
+            'description',
+            existing_type=sa.String(length=5000),
+            type_=sa.Text(length=5000),
+            existing_nullable=True,
+        )
+    else:
+        # postgres does not allow size modifier for text type
+        op.alter_column('connection', 'description', existing_type=sa.String(length=5000), type_=sa.Text())
+
+
+def downgrade():
+    """Unapply fix description field in connection to be text"""
+    conn = op.get_bind()  # pylint: disable=no-member
+    if conn.dialect.name == "sqlite":
+        # in sqlite TEXT and STRING column types are the same
+        return
+    if conn.dialect.name == "mysql":
+        op.alter_column(
+            'connection',
+            'description',
+            existing_type=sa.Text(5000),
+            type_=sa.String(length=5000),
+            existing_nullable=True,
+        )
+    else:
+        # postgres does not allow size modifier for text type
+        op.alter_column(
+            'connection',
+            'description',
+            existing_type=sa.Text(),
+            type_=sa.String(length=5000),
+            existing_nullable=True,
+        )

airflow/models/connection.py

@@ -22,7 +22,7 @@
 from typing import Dict, List, Optional
 from urllib.parse import parse_qsl, quote, unquote, urlencode, urlparse
 
-from sqlalchemy import Boolean, Column, Integer, String
+from sqlalchemy import Boolean, Column, Integer, String, Text
 from sqlalchemy.ext.declarative import declared_attr
 from sqlalchemy.orm import synonym
 
@@ -154,7 +154,7 @@ class Connection(Base, LoggingMixin):  # pylint: disable=too-many-instance-attri
     id = Column(Integer(), primary_key=True)
     conn_id = Column(String(ID_LEN), unique=True, nullable=False)
     conn_type = Column(String(500), nullable=False)
-    description = Column(String(5000))
+    description = Column(Text(5000))
     host = Column(String(500))
     schema = Column(String(500))
     login = Column(String(500))