I'm working on a project with Flask, SQLAlchemy, Alembic and their wrappers for Flask (Flask-SQLAlchemy and Flask-Migrate). I have four migrations:
1c5f54d4aa34 -> 4250dfa822a4 (head), Feed: Countries
312c1d408043 -> 1c5f54d4aa34, Feed: Continents
41984a51dbb2 -> 312c1d408043, Basic Structure
<base> -> 41984a51dbb2, Init Alembic
When I start a new and clean database and try to run the migrations I get an error:
vagrant@precise32:/vagrant$ python manage.py db upgrade
...
sqlalchemy.exc.ProgrammingError: (ProgrammingError) relation "continent" does not exist
...
If I ask Flask-Migrate to run all migrations but the last, it works. If after that I run the upgrade command again, it works – that is, it fully upgrades my database without a single change in code:
vagrant@precise32:/vagrant$ python manage.py db upgrade 312c1d408043
INFO [alembic.migration] Context impl PostgresqlImpl.
INFO [alembic.migration] Will assume transactional DDL.
INFO [alembic.migration] Running upgrade -> 41984a51dbb2, Init Alembic
INFO [alembic.migration] Running upgrade 41984a51dbb2 -> 312c1d408043, Basic Structure
vagrant@precise32:/vagrant$ python manage.py db upgrade
INFO [alembic.migration] Context impl PostgresqlImpl.
INFO [alembic.migration] Will assume transactional DDL.
INFO [alembic.migration] Running upgrade 312c1d408043 -> 1c5f54d4aa34, Feed: Continents
INFO [alembic.migration] Running upgrade 1c5f54d4aa34 -> 4250dfa822a4, Feed: Countries
TL;DR
The last migration (Feed: Countries) run queries on the table fed by the previous one (Feed: Continents). If I have the continents table create and fed, the scripts should work. But it doesn't. Why do I have to stop the migration process between then to re-start it in another command? I really don't get this. Is it some command Alembic executes after a serie of migrations? Any ideas?
Just in case
My models are defined as follows:
class Country(db.Model):
__tablename__ = 'country'
id = db.Column(db.Integer, primary_key=True)
alpha2 = db.Column(db.String(2), index=True, unique=True)
title = db.Column(db.String(140))
continent_id = db.Column(db.Integer, db.ForeignKey('continent.id'))
continent = db.relationship('Continent', backref='countries')
def __repr__(self):
return '<Country #{}: {}>'.format(self.id, self.title)
class Continent(db.Model):
__tablename__ = 'continent'
id = db.Column(db.Integer, primary_key=True)
alpha2 = db.Column(db.String(2), index=True, unique=True)
title = db.Column(db.String(140))
def __repr__(self):
return '<Continent #{}: {}>'.format(self.id, self.title)
Many thanks,
UPDATE 1: The upgrade method of the last two migrations
As @Miguel asked in a comment, here there are the upgrade methods of the last two migrations:
Feed: Continents
def upgrade():
csv_path = app.config['BASEDIR'].child('migrations', 'csv', 'en')
csv_file = csv_path.child('continents.csv')
with open(csv_file) as file_handler:
csv = list(reader(file_handler))
csv.pop(0)
data = [{'alpha2': c[0].lower(), 'title': c[1]} for c in csv]
op.bulk_insert(Continent.__table__, data)
Feed: Countries (which depends on the table fed on the last migration)
def upgrade():
# load countries iso3166.csv and build a dictionary
csv_path = app.config['BASEDIR'].child('migrations', 'csv', 'en')
csv_file = csv_path.child('iso3166.csv')
countries = dict()
with open(csv_file) as file_handler:
csv = list(reader(file_handler))
for c in csv:
countries[c[0]] = c[1]
# load countries-continents from country_continent.csv
csv_file = csv_path.child('country_continent.csv')
with open(csv_file) as file_handler:
csv = list(reader(file_handler))
country_continent = [{'country': c[0], 'continent': c[1]} for c in csv]
# loop
data = list()
for item in country_continent:
# get continent id
continent_guess = item['continent'].lower()
continent = Continent.query.filter_by(alpha2=continent_guess).first()
# include country
if continent is not None:
country_name = countries.get(item['country'], False)
if country_name:
data.append({'alpha2': item['country'].lower(),
'title': country_name,
'continent_id': continent.id})
The CSV I'm using are basically following this patterns:
continents.csv
...
AS, "Asia"
EU, "Europe"
NA, "North America"
...
iso3166.csv
...
CL,"Chile"
CM,"Cameroon"
CN,"China"
...
_country_continent.csv_
...
US,NA
UY,SA
UZ,AS
...
So Feed: Continents feeds the continent table, and Feed: Countries feeds the country table. But it has to query the continents table in order to make the proper link between the country and the continent.
UPDATE 2: Some one from Reddit already offered an explanation and a workaround
I asked the same question on Reddit, and themathemagician said:
I've run into this before, and the issue is that the migrations don't execute individually, but instead alembic batches all of them (or all of them that need to be run) and then executes the SQL. This means that by the time the last migration is trying to run, the tables don't actually exist yet so you can't actually make queries. Doing
from alembic import op def upgrade(): #migration stuff op.execute('COMMIT') #run queriesThis isn't the most elegant solution (and that was for Postgres, the command may be different for other dbs), but it worked for me. Also, this isn't actually an issue with Flask-Migrate as much as an issue with alembic, so if you want to Google for more info, search for alembic. Flask-Migrate is just a wrapper around alembic that works with Flask-Script easily.