Flask, prevent SQLAlchemy from adding values that are not specified when instantiating mapped classes

Question

I have this class:

class Payment(db.Model):
    __tablename__ = "payment"
    id = db.Column("payment_id", db.Integer, primary_key=True, autoincrement=True)
    date = db.Column("payment_date", db.DateTime)
    payment_collected = db.Column(db.Integer)
    amount_collected = db.Column(db.String(15))
    payment_type_id = db.Column("payment_type", db.Integer)
    reference_number = db.Column(db.String(255))
    is_invoice_data = db.Column(db.Integer)
    is_active = db.Column(db.Integer)
    payee_user_id = db.Column(db.Integer, db.ForeignKey("user.user_id"))
    services_rendered_id = db.Column(
        db.Integer, db.ForeignKey("services_rendered.service_id")
    )

which maps directly to a table in my database. The column payment_date (represented by the date property on the class) is set to default to CURRENT_TIMESTAMP. However, when calling this class as a constructor like:

new_payment = Payment(
    services_rendered_id=new_sr.id,
    payment_collected=True,
    payment_type_id=payment_type_id,
    payee_user_id=payee_id,
    amount_collected=amount_collected
)

the generated SQL inserts a value to ALL the map columns, including payment_date, and passes None for those columns that I do not specify in the constructor.

Example:

INSERT INTO 
    payment 
        (payment_date, payment_collected, amount_collected, payment_type, reference_number, is_invoice_data, is_active, payee_user_id, services_rendered_id) 
    VALUES 
        (None, 1, '258.40', '7', None, None, None, 3240, 28)

How could I avoid this behavior so that SQLAlchemy does not override the default values I've set in my database?

jwodder · Accepted Answer · 2018-12-06 21:45:26Z

1

Setting server_default=db.FetchedValue() for the date column will tell SQLAlchemy to get the default value for the column from the database upon INSERT. See the documentation for further information.

answered Dec 6, 2018 at 21:45

jwodder

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1 Comment

Robbie Milejczak Over a year ago

Awesome thank you! And thanks for the doc link, sql alchemy docs are so dense I sometimes have trouble finding the info I need

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