SQLAlchemy default vs server_dafault

When defining a SQLAlchemy model, there're two main categories the ways we can assign default values to columns.

Client side

1. Use default parameter.
2. Pass a scalar value, such as 0 or True:

points: Column = Column(Integer, default=0)

The value will be used in an INSERT statement.

For example, when we define a model with an empty points and insert it into DB, it would carry a default value 0 from the client side.

The DB shcema has no default value.

See more details: https://docs.sqlalchemy.org/en/14/core/defaults.html#scalar-defaults

Server side

1. User server_default parameter.
2. Pass a text value, such as "0"or "2022-05-25"(Integer or Date value would cause an error):

points: Column = Column(Integer, server_default="0")

The value will be used in the CREATE TABLE statement.

For example, when we define a model with an empty points and insert it into DB, it would carry nothing from the client side, while the DB server would create a default value for it.

The DB shcema has the default value.

See more detalis: https://docs.sqlalchemy.org/en/14/core/defaults.html#server-invoked-ddl-explicit-default-expressions

Summary

Note that default has a different functionality (happens in python and not in DB) thus in most cases using server_default would be a better choice.