Invoke method on SQLite connection in Flask-SQLAlchemy

Question

I'm developing a web app with Flask-SQLAlchemy backed by a SQLite database. I need to call a method (create_collation) right after connecting. Without the SQLAlchemy framework, I can do that like this:

conn = sqlite3.connect(path)
conn.create_collation('my_collate', my_collate)
# ... go on and do fancy "order_by" stuff.

How do I do that in Flask-SQLAlchemy? Based on the API I was thinking of the following, but I get AttributeError: 'Engine' object has no attribute 'create_collation'.

from flask_sqlalchemy import SQLAlchemy

class MySQLAlchemy(SQLAlchemy):
    def create_engine(self, sa_url, engine_opts):
        engine = super().create_engine(sa_url, engine_opts)
        engine.create_collation('my_collate', self.my_collate)
        return engine

    @staticmethod
    def my_collate(string1, string2):
        return string1.locateCompare(string2)

Following the SQLAlchemy docs I think I need to get the connection rather than the engine. But I can't find out how.

Also, where should this go specifically in Flask-SQLAlchemy? What part ultimately "connect"s, and how do I tune into that?

Janne Karila · Accepted Answer · 2019-09-13 10:41:06Z

3

SQLAlchemy has an Events API that allows you to create a function that will be called whenever the connection pool creates a new connection:

from sqlalchemy.event import listens_for
from sqlalchemy.pool import Pool

@listens_for(Pool, "connect")
def my_on_connect(dbapi_con, connection_record):
    dbapi_con.create_collation('my_collate', my_collate)

answered Sep 13, 2019 at 10:41

Janne Karila

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