fix: drop check constraint on dbs to rename column

[betodealmeida]

SUMMARY

The migration in #16756 is failing in MySQL 8. Renaming the column dbs.allow_csv_upload fails because there's a check constraint on it.

This seems to be a known bug (sqlalchemy/alembic#699), and from that thread dropping the constraint seems safe. The problem is that existing installations already have the constraint, so we can't add create_constraint=False to boolean columns in the model.

This PR fixes the migration by explicitly dropping the check constraint if it exists, and renaming the column after.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

Install Superset using a MySQL 8 database. The superset db upgrade step will fail on the migration b92d69a6643c_rename_csv_to_file.py.

With this PR, the check constraint is dropped and the migration succeeds.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #17275 (3d66523) into master (37909aa) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #17275      +/-   ##
==========================================
- Coverage   77.02%   77.02%   -0.01%     
==========================================
  Files        1037     1037              
  Lines       55629    55629              
  Branches     7594     7594              
==========================================
- Hits        42850    42848       -2     
- Misses      12529    12531       +2     
  Partials      250      250              

Flag	Coverage Δ
hive	81.52% <ø> (ø)
mysql	81.95% <ø> (ø)
postgres	81.96% <ø> (ø)
presto	81.82% <ø> (-0.01%)	⬇️
python	82.45% <ø> (-0.01%)	⬇️
sqlite	81.63% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/db_engine_specs/presto.py	89.95% <0.00%> (-0.42%)	⬇️

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[exemplary-citizen]

Alternatively, we can change the original db migration to not create a constraint in revision 1d9e835a84f9

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Revision ID: 1d9e835a84f9
Revises: 3dda56f1c4c6
Create Date: 2018-07-16 18:04:07.764659

"""
import sqlalchemy as sa
from alembic import op
from sqlalchemy.sql import expression

# revision identifiers, used by Alembic.
revision = "1d9e835a84f9"
down_revision = "3dda56f1c4c6"


def upgrade():
    op.add_column(
        "dbs",
        sa.Column(
            "allow_csv_upload",
            sa.Boolean(create_constraint=False),
            nullable=False,
            server_default=expression.true(),
        ),
    )


def downgrade():
    op.drop_column("dbs", "allow_csv_upload")

[betodealmeida]

Alternatively, we can change the original db migration to not create a constraint in revision 1d9e835a84f9

Unfortunately that would work only for fresh installs. Everyone already using Superset has the constraint set in their databases, and if they're running it under MySQL 8 the only way to upgrade their DB with your migration is to drop the constraint.