unable to create autoincrementing primary key with flask-sqlalchemy

Question

I want my model\'s primary key to be an autoincrementing integer. Here is how my model looks like

class Region(db.Model):
    __tablename__ = \'regions\'
            


        

Answer 1

So I landed here with an issue that my SQLite table wasn't auto-incrementing the primary key. I have a slightly complex use case where I want to use postgres in production but sqlite for testing to make life a bit easier when continuously deploying.

It turns out SQLite doesn't like columns defined as BigIntegers, and for incrementing to work they should be set as Integers. Remarkably SQLAlchemy can handle this scenario as follows using the with_variant function. Thought this may be useful for someone:

id = db.Column(db.BigInteger().with_variant(db.Integer, "sqlite"), primary_key=True)

Further details here https://docs.sqlalchemy.org/en/13/dialects/sqlite.html

Answer 2

Nothing is wrong with the above code. In fact, you don't even need autoincrement=True or db.Sequence('seq_reg_id', start=1, increment=1), as SQLAlchemy will automatically set the first Integer PK column that's not marked as a FK as autoincrement=True.

Here, I've put together a working setup based on yours. SQLAlechemy's ORM will take care of generating id's and populating objects with them if you use the Declarative Base based class that you've defined to create instances of your object.

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.debug = True
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://user:password@localhost/testdb'
app.config['SQLALCHEMY_ECHO'] = True
db = SQLAlchemy(app)

class Region(db.Model):
    __tablename__ = 'regions'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(100))

db.drop_all()
db.create_all()

region = Region(name='Over Yonder Thar')
app.logger.info(region.id) # currently None, before persistence

db.session.add(region)
db.session.commit()
app.logger.info(region.id) # gets assigned an id of 1 after being persisted

region2 = Region(name='Yet Another Up Yar')
db.session.add(region2)
db.session.commit()
app.logger.info(region2.id) # and 2

if __name__ == '__main__':
    app.run(port=9001)

Answer 3

I had this issue declaring Composite Keys on a model class.

If you are wanting an auto-incrementing id field for a composite key (ie. more than 1 db.Column(..) definition with primary_key=True, then adding autoincrement=True fixed the issue for me.

class S3Object(db.Model):
    __tablename__ = 's3_object'

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)

    # composite keys
    bucket_name = db.Column(db.String(), primary_key=True)
    key = db.Column(db.String(), primary_key=True)

So the statements above about not requiring autoincrement=True should be :

you don't even need autoincrement=True, as SQLAlchemy will automatically set the first Integer PK column that's not marked as a FK as autoincrement=True unless you are defining a composite key with more than one primary_key=True

Answer 4

I had the same error, even after adding autoincrement=True.

The problem was I already had the migration created. So I downgraded to the previous migration, deleted the migration, created the migration again and upgraded.

Then the error was gone.

Hope it helps someone stuck on this.

Wrapping off: Add autoincrement=True, and ensure your migration is updated and applied.

Answer 5

Your id auto increments by default even without setting the autoincrement=True flag.

So there's nothing wrong with using

id = db.Column(db.Integer, primary_key=True, autoincrement=True)

The error you're getting is as a result of attempting to populate the table with an id attribute. Your insert query shouldn't at any point contain an id attribute otherwise you'll get that error.

Answer 6

I think you do not need the autoincrement once you set ,

id = db.Column(db.Integer , primary_key=True , autoincrement=True)

I think that it should be ,

id = db.Column(db.Integer , primary_key=True)

it will give you the uniqueness your looking for .