Mysql key length

[x4base]

Attempt to fix #449

[landscape-bot]

Code quality remained the same when pulling d4c3ffa on x4base:mysql_key_length into 6c333d5 on airbnb:master.

[coveralls]

Coverage remained the same at 81.627% when pulling d4c3ffa on x4base:mysql_key_length into 6c333d5 on airbnb:master.

[mistercrunch]

Looks good, though I don't think you should alter the previous migration scripts.

[x4base]

For clean install, Alembic will iterate through all the migration scripts, from the oldest to the newest. If I don't alter the previous ones, The migration will crash on the very first migration script "4e6a06bad7a8_init.py" (see traceback below).
So I altered the previous scripts and created the new script because:

1. For clean install: It prevents the migration from crashing.
2. For those who are upgrading there existing SQLite: Alembic starts the iteration from the current version of the SQLite according to version_num in the alembic_versions table, so the previous migration scripts that I altered won't do any harm to the existing database.
   So I think it's ok to alter the previous ones.

Traceback:

caravel db upgrade head
....
INFO [alembic.runtime.migration] Running upgrade -> 4e6a06bad7a8, Init
Traceback (most recent call last):
File "/Users/clu/.pyenv/versions/druid/bin/caravel", line 6, in <module>
exec(compile(open(__file__).read(), __file__, 'exec'))
File "/projects/druid/panoramix/caravel/bin/caravel", line 113, in <module>
manager.run()
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/Flask_Script-2.0.5-py2.7.egg/flask_script/__init__.py", line 412, in run
result = self.handle(sys.argv[0], sys.argv[1:])
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/Flask_Script-2.0.5-py2.7.egg/flask_script/__init__.py", line 383, in handle
res = handle(*args, **config)
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/Flask_Script-2.0.5-py2.7.egg/flask_script/commands.py", line 216, in __call__
return self.run(*args, **kwargs)
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/Flask_Migrate-1.8.0-py2.7.egg/flask_migrate/__init__.py", line 235, in upgrade
command.upgrade(config, revision, sql=sql, tag=tag)
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/command.py", line 174, in upgrade
script.run_env()
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/script/base.py", line 397, in run_env
util.load_python_file(self.dir, 'env.py')
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/util/pyfiles.py", line 81, in load_python_file
module = load_module_py(module_id, path)
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/util/compat.py", line 79, in load_module_py
mod = imp.load_source(module_id, path, fp)
File "/projects/druid/panoramix/caravel/migrations/env.py", line 91, in <module>
run_migrations_online()
File "/projects/druid/panoramix/caravel/migrations/env.py", line 84, in run_migrations_online
context.run_migrations()
File "<string>", line 8, in run_migrations
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/runtime/environment.py", line 797, in run_migrations
self.get_context().run_migrations(**kw)
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/runtime/migration.py", line 312, in run_migrations
step.migration_fn(* *kw)
File "/projects/druid/panoramix/caravel/migrations/versions/4e6a06bad7a8_init.py", line 71, in upgrade
sa.UniqueConstraint('datasource_name')
File "<string>", line 8, in create_table
File "<string>", line 3, in create_table
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/operations/ops.py", line 1098, in create_table
return operations.invoke(op)
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/operations/base.py", line 318, in invoke
return fn(self, operation)
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/operations/toimpl.py", line 101, in create_table
operations.impl.create_table(table)
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/ddl/impl.py", line 194, in create_table
self._exec(schema.CreateTable(table))
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/alembic-0.8.5-py2.7.egg/alembic/ddl/impl.py", line 118, in _exec
return conn.execute(construct, *multiparams, **params)
File "build/bdist.macosx-10.9-x86_64/egg/sqlalchemy/engine/base.py", line 914, in execute
File "build/bdist.macosx-10.9-x86_64/egg/sqlalchemy/sql/ddl.py", line 68, in _execute_on_connection
File "build/bdist.macosx-10.9-x86_64/egg/sqlalchemy/engine/base.py", line 968, in _execute_ddl
File "build/bdist.macosx-10.9-x86_64/egg/sqlalchemy/engine/base.py", line 1146, in _execute_context
File "build/bdist.macosx-10.9-x86_64/egg/sqlalchemy/engine/base.py", line 1341, in _handle_dbapi_exception
File "build/bdist.macosx-10.9-x86_64/egg/sqlalchemy/util/compat.py", line 200, in raise_from_cause
File "build/bdist.macosx-10.9-x86_64/egg/sqlalchemy/engine/base.py", line 1139, in _execute_context
File "build/bdist.macosx-10.9-x86_64/egg/sqlalchemy/engine/default.py", line 450, in do_execute
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/MySQLdb/cursors.py", line 226, in execute
self.errorhandler(self, exc, value)
File "/Users/clu/.pyenv/versions/druid/lib/python2.7/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
raise errorvalue
sqlalchemy.exc.OperationalError: (_mysql_exceptions.OperationalError) (1071, 'Specified key was too long; max key length is 767 bytes') [SQL: u'\nCREATE TABLE datasources (\n\tcreated_on DATETIME NOT NULL, \n\tchanged_on DATETIME NOT NULL, \n\tid INTEGER NOT NULL AUTO_INCREMENT, \n\tdatasource_name VARCHAR(256), \n\tis_featured BOOL, \n\tis_hidden BOOL, \n\tdescription TEXT, \n\tdefault_endpoint TEXT, \n\tuser_id INTEGER, \n\tcluster_name VARCHAR(250), \n\tcreated_by_fk INTEGER, \n\tchanged_by_fk INTEGER, \n\tPRIMARY KEY (id), \n\tUNIQUE (datasource_name), \n\tCHECK (is_featured IN (0, 1)), \n\tCHECK (is_hidden IN (0, 1)), \n\tFOREIGN KEY(user_id) REFERENCES ab_user (id), \n\tFOREIGN KEY(cluster_name) REFERENCES clusters (cluster_name), \n\tFOREIGN KEY(created_by_fk) REFERENCES ab_user (id), \n\tFOREIGN KEY(changed_by_fk) REFERENCES ab_user (id)\n)\n\n']

[mistercrunch]

Ok, let's roll with it then!