[dashboards] Increasing position_json to MEDIUMTEXT for MySQL (#5618)

superset/migrations/versions/1a1d627ebd8e_position_json.py

@@ -0,0 +1,36 @@
+"""position_json
+
+Revision ID: 1a1d627ebd8e
+Revises: 0c5070e96b57
+Create Date: 2018-08-13 11:30:07.101702
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '1a1d627ebd8e'
+down_revision = '0c5070e96b57'
+
+from alembic import op
+import sqlalchemy as sa
+
+from superset.utils import MediumText
+
+
+def upgrade():
+    with op.batch_alter_table('dashboards') as batch_op:
+        batch_op.alter_column(
+            'position_json',
+            existing_type=sa.Text(),
+            type_=MediumText(),
+            existing_nullable=True,
+        )
+
+
+def downgrade():
+    with op.batch_alter_table('dashboards') as batch_op:
+        batch_op.alter_column(
+            'position_json',
+            existing_type=MediumText(),
+            type_=sa.Text(),
+            existing_nullable=True,
+        )