Set conn_type as not-nullable

UPDATING.md

@@ -62,6 +62,14 @@ https://developers.google.com/style/inclusive-documentation
 
 -->
 
+### Not-nullable conn_type collumn in connection table
+
+The `conn_type` column in the `connection` table must contain content. Previously, this rule was enforced
+by application logic, but was not enforced by the database schema.
+
+If you made any modifications to the table directly, make sure you don't have
+null in the conn_type column.
+
 ### DAG.create_dagrun accepts run_type and does not require run_id
 This change is caused by adding `run_type` column to `DagRun`.
 

airflow/migrations/versions/8f966b9c467a_set_conn_type_as_non_nullable.py

@@ -0,0 +1,47 @@
+#
+# 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.
+
+"""Set conn_type as non-nullable
+
+Revision ID: 8f966b9c467a
+Revises: 3c20cacc0044
+Create Date: 2020-06-08 22:36:34.534121
+
+"""
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "8f966b9c467a"
+down_revision = "3c20cacc0044"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    """Apply Set conn_type as non-nullable"""
+
+    with op.batch_alter_table("connection", schema=None) as batch_op:
+        batch_op.alter_column("conn_type", existing_type=sa.VARCHAR(length=500), nullable=False)
+
+
+def downgrade():
+    """Unapply Set conn_type as non-nullable"""
+    with op.batch_alter_table("connection", schema=None) as batch_op:
+        batch_op.alter_column("conn_type", existing_type=sa.VARCHAR(length=500), nullable=True)

airflow/models/connection.py

@@ -109,7 +109,7 @@ class Connection(Base, LoggingMixin):
 
     id = Column(Integer(), primary_key=True)
     conn_id = Column(String(ID_LEN))
-    conn_type = Column(String(500))
+    conn_type = Column(String(500), nullable=False)
     host = Column(String(500))
     schema = Column(String(500))
     login = Column(String(500))