[migration] add unique constraint on dashboard_slices table (#7880)

1. remove duplicated entries in many-to-many relation tbl dashboard_slices
2. add unique constraint on tbl
3. update the model to include the uniqueness constraint

superset/migrations/versions/190188938582_adding_unique_constraint_on_dashboard_slices_tbl.py

@@ -0,0 +1,100 @@
+# 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.
+"""Remove duplicated entries in dashboard_slices table and add unique constraint
+
+Revision ID: 190188938582
+Revises: d6ffdf31bdd4
+Create Date: 2019-07-15 12:00:32.267507
+
+"""
+import logging
+
+from alembic import op
+from sqlalchemy import and_, Column, ForeignKey, Integer, Table
+from sqlalchemy.ext.declarative import declarative_base
+
+from superset import db
+
+# revision identifiers, used by Alembic.
+revision = "190188938582"
+down_revision = "d6ffdf31bdd4"
+
+Base = declarative_base()
+
+
+class DashboardSlices(Base):
+    __tablename__ = "dashboard_slices"
+    id = Column(Integer, primary_key=True)
+    dashboard_id = Column(Integer, ForeignKey("dashboards.id"))
+    slice_id = Column(Integer, ForeignKey("slices.id"))
+
+
+def upgrade():
+    bind = op.get_bind()
+    session = db.Session(bind=bind)
+
+    # find dup records in dashboard_slices tbl
+    dup_records = (
+        session.query(
+            DashboardSlices.dashboard_id,
+            DashboardSlices.slice_id,
+            db.func.count(DashboardSlices.id),
+        )
+        .group_by(DashboardSlices.dashboard_id, DashboardSlices.slice_id)
+        .having(db.func.count(DashboardSlices.id) > 1)
+        .all()
+    )
+
+    # remove dup entries
+    for record in dup_records:
+        print(
+            "remove duplicates from dashboard {} slice {}".format(
+                record.dashboard_id, record.slice_id
+            )
+        )
+
+        ids = [
+            item.id
+            for item in session.query(DashboardSlices.id)
+            .filter(
+                and_(
+                    DashboardSlices.slice_id == record.slice_id,
+                    DashboardSlices.dashboard_id == record.dashboard_id,
+                )
+            )
+            .offset(1)
+        ]
+        session.query(DashboardSlices).filter(DashboardSlices.id.in_(ids)).delete(
+            synchronize_session=False
+        )
+
+    # add unique constraint
+    try:
+        with op.batch_alter_table("dashboard_slices") as batch_op:
+            batch_op.create_unique_constraint(
+                "uq_dashboard_slice", ["dashboard_id", "slice_id"]
+            )
+    except Exception as e:
+        logging.exception(e)
+
+
+def downgrade():
+    try:
+        with op.batch_alter_table("dashboard_slices") as batch_op:
+            batch_op.drop_constraint("uq_dashboard_slice", type_="unique")
+    except Exception as e:
+        logging.exception(e)

superset/models/core.py

@@ -395,6 +395,7 @@ dashboard_slices = Table(
     Column("id", Integer, primary_key=True),
     Column("dashboard_id", Integer, ForeignKey("dashboards.id")),
     Column("slice_id", Integer, ForeignKey("slices.id")),
+    UniqueConstraint("dashboard_id", "slice_id"),
 )
 
 dashboard_user = Table(