Fix LargeBinary column type for mysql

Currently sqlalchemy has a bug with mysql and LargeBinary type
fails to create LongBlob and creates Blob instead [1].

As a workaround it's recommended to explicitly specify column
type and size for mysql deployments [2].

[1] https://bitbucket.org/zzzeek/sqlalchemy/issues/3883/largebinary-type-fails-to-create-longblob
[2] https://stackoverflow.com/questions/43791725/sqlalchemy-how-to-make-a-longblob-column-in-mysql

Change-Id: I921a5ae86ced07ac0a04ba7e5dafcea07afebdb0

glare/db/migration/alembic_migrations/versions/003_add_database_blob_storage.py

@@ -27,6 +27,7 @@ down_revision = '002'
 
 from alembic import op
 import sqlalchemy as sa
+from sqlalchemy.dialects import mysql
 
 MYSQL_ENGINE = 'InnoDB'
 MYSQL_CHARSET = 'utf8'
@@ -36,7 +37,13 @@ def upgrade():
     op.create_table(
         'glare_blob_data',
         sa.Column('id', sa.String(255), primary_key=True, nullable=False),
-        sa.Column('data', sa.LargeBinary(), nullable=False),
+        # Because of strange behavior of mysql LargeBinary is converted to
+        # BLOB instead of LONGBLOB. So we have to fix it explicitly with
+        # 'with_variant' call.
+        sa.Column(
+            'data',
+            sa.LargeBinary().with_variant(mysql.LONGBLOB(), 'mysql'),
+            nullable=False),
         sa.PrimaryKeyConstraint('id'),
         mysql_engine=MYSQL_ENGINE,
         mysql_charset=MYSQL_CHARSET

glare/db/sqlalchemy/models.py

@@ -252,7 +252,7 @@ class ArtifactBlobData(BASE, ArtifactBase):
     __table_args__ = (
         {'mysql_engine': 'InnoDB', 'mysql_charset': 'utf8'},)
     id = Column(String(255), primary_key=True, nullable=False)
-    data = Column(LargeBinary, nullable=False)
+    data = Column(LargeBinary(length=(2 ** 32) - 1), nullable=False)
 
 
 def register_models(engine):