SQLAlchemy with MySQL won't auto increment - mysql

Question

I'm using MySQL 8.0 and SQLAlchemy. My id column isn't incrementing, and I don't understand why.
SQLAlchemy Model:
class Show(db.Model):
__tablename__ = "shows"
id = Column(Integer, primary_key=True, index=True)
name = Column(String)
type = Column(String)
status = Column(String)
episodes = Column(Integer)
series_entry_id = Column(Integer, ForeignKey("series.id"))
series_id = Column(Integer, ForeignKey("series.id"))
lists = relationship("List", secondary=show_list, back_populates="shows")
recommendations = relationship("Recommendation", backref=backref("shows"))
user_ratings = relationship("Rating", backref=backref("shows"))
alt_names = relationship("User", secondary=alt_names, back_populates="alt_show_names")
series_entry = relationship("Series", foreign_keys=[series_entry_id], uselist=False)
series = relationship("Series", foreign_keys=[series_id], post_update=True)
Breaking code:
show = Show(
name=new_data["title"]["english"],
type=new_data["format"],
status=new_data["status"],
episodes=new_data["episodes"],
)
db.session.add(show)
db.session.commit()
The original error I received was:
sqlalchemy.exc.DatabaseError: (mysql.connector.errors.DatabaseError) 1364 (HY000):
Field 'id' doesn't have a default value
From this answer, I added the index parameter to my id column and edited the my.ini file to take it out of STRICT_TRANS_TABLES mode. The new error is:
sqlalchemy.exc.IntegrityError: (mysql.connector.errors.IntegrityError) 1062 (23000):
Duplicate entry '0' for key 'shows.PRIMARY'
All answers I've found on the topic talk about AUTO_INCREMENT, but the SQLAlchemy docs say that that should be the default here, given that it's an integer primary key without it specified to false. I did try adding autoincrement=True just in case, but when I tried to migrate it alembic told me that no changes were detected.

Answer 1

From comments to the question:
does this mean that SQLAlchemy is wrong and [AUTO_INCREMENT] isn't set by default [for the first integer primary key column]?
No, that is indeed how it works. Specifically, for a model like
class Account(Base):
__tablename__ = "account"
account_number = Column(Integer, primary_key=True)
customer_name = Column(String(50))
alembic revision --autogenerate will generate
def upgrade():
# ### commands auto generated by Alembic - please adjust! ###
op.create_table('account',
sa.Column('account_number', sa.Integer(), nullable=False),
sa.Column('customer_name', sa.String(length=50), nullable=True),
sa.PrimaryKeyConstraint('account_number')
)
(which doesn't explicitly specify autoincrement=) but when alembic upgrade head gets SQLAlchemy to actually create the table SQLAlchemy emits
CREATE TABLE account (
account_number INTEGER NOT NULL AUTO_INCREMENT,
customer_name VARCHAR(50),
PRIMARY KEY (account_number)
)
Since alembic didn't detect any changes when I set autoincrement=True, does that mean that for every table I make, I'll have to set AUTO_INCREMENT in the database manually?
No. As illustrated above, Alembic properly handles AUTO_INCREMENT when the table is first created. What it doesn't detect is when an ORM model with an existing table has a column changed from autoincrement=False to autoincrement=True (or vice versa).
This is known behaviour, as indicated by the commit message here:
"Note that this flag does not support alteration of a column's "autoincrement" status, as this is not portable across backends."
MySQL does support changing the AUTO_INCREMENT property of a column via ALTER_TABLE, so we could achieve that by changing the "empty" upgrade method
def upgrade():
# ### commands auto generated by Alembic - please adjust! ###
pass
# ### end Alembic commands ###
to
def upgrade():
op.alter_column(
'account',
'account_number',
existing_type=sa.Integer(),
existing_nullable=False,
autoincrement=True
)
which renders
ALTER TABLE account MODIFY account_number INTEGER NOT NULL AUTO_INCREMENT