[pie-chart] Restricting query to single metric (#5203)

superset/assets/src/explore/visTypes.js

@@ -161,7 +161,7 @@ export const visTypes = {
         label: t('Query'),
         expanded: true,
         controlSetRows: [
-          ['metrics'],
+          ['metric'],
           ['adhoc_filters'],
           ['groupby'],
           ['limit'],

superset/migrations/versions/80a67c5192fa_single_pie_chart_metric.py

@@ -0,0 +1,73 @@
+"""single pie chart metric
+
+Revision ID: 80a67c5192fa
+Revises: afb7730f6a9c
+Create Date: 2018-06-14 14:31:06.624370
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '80a67c5192fa'
+down_revision = 'afb7730f6a9c'
+
+
+import json
+
+from alembic import op
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy import Column, Integer, String, Text
+
+from superset import db
+
+
+Base = declarative_base()
+
+
+class Slice(Base):
+    __tablename__ = 'slices'
+
+    id = Column(Integer, primary_key=True)
+    params = Column(Text)
+    viz_type = Column(String(250))
+
+
+def upgrade():
+    bind = op.get_bind()
+    session = db.Session(bind=bind)
+
+    for slc in session.query(Slice).filter(Slice.viz_type == 'pie').all():
+        try:
+            params = json.loads(slc.params)
+
+            if 'metrics' in params:
+                if params['metrics']:
+                    params['metric'] = params['metrics'][0]
+
+                del params['metrics']
+                slc.params = json.dumps(params, sort_keys=True)
+        except Exception:
+            pass
+
+    session.commit()
+    session.close()
+
+
+def downgrade():
+    bind = op.get_bind()
+    session = db.Session(bind=bind)
+
+    for slc in session.query(Slice).filter(Slice.viz_type == 'pie').all():
+        try:
+            params = json.loads(slc.params)
+
+            if 'metric' in params:
+                if params['metric']:
+                    params['metrics'] = [params['metric']]
+
+                del params['metric']
+                slc.params = json.dumps(params, sort_keys=True)
+        except Exception:
+            pass
+
+    session.commit()
+    session.close()