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How to create a time Field for a model like django DateTimeField #370
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There are a few ways to do this, either via Pydantic or with SQLAlchemy.
SQLAlchemy is the way to go since implementing
updated_atin it seems easier, but I'll leave the Pydantic approach here anyway since I wrote it first 😛With Pydantic default factories or validators
With Pydantic you could use default factories:
from datetime import datetime from pydantic import BaseModel, Field class Model(BaseModel): created_at: datetime = Field(default_factory=datetime.utcnow) m1 = Model() m2 = Model() print(f'{m1.created_at} != {m2.created_at}') #> 2022-05-19 10:49:22.053624 != 2022-05-19 10:49:22.053641
Another approach would be validators:
from datetime import datetime from pydantic import BaseModel, validator class Model(BaseModel): created_at: datetime = None @validator('ts', pre=True, always=True) def set_created_at_now(cls, v): return v or datetime.now()
Having an automatic update time is a bit tougher... I think it should be possible with validators, but I can think of a few cases where the incorrect time can be set.
Doing this in SQLAlchemy is easy using
server_defaultandon_update:from sqlalchemy.sql import func time_created = Column(DateTime(timezone=True), server_default=func.now()) time_updated = Column(DateTime(timezone=True), onupdate=func.now())
The above column definitions would mean that if
time_createdisNone, thenfunc.now()is the default, and iftime_updatedis changed, then its value will be overwritten withfunc.now().Since you can directly use SQLAlchemy Columns in an SQLModel Field with the keyword argument
sa_column, the above can just be copy/pasted into an SQLModel model:from sqlmodel import Field, SQLModel from sqlalchemy.sql import func from sqlalchemy import Column, DateTime class Model(SQLModel, table=True): id: Optional[int] = Field(default=None, primary_key=True) foo: Optional[str] created_at: Optional[datetime] = Field( sa_column=Column(DateTime(timezone=True), server_default=func.now()) ) updated_at: Optional[datetime] = Field( sa_column=Column(DateTime(timezone=True), onupdate=func.now()) )
Gave it a quick test and it seems to work correctly, when an instance of
Modelis first added and committedcreated_atis set to the current time andupdated_atisNone, then iffoois changed and the change is saved,updated_atis set to the time the save was done andcreated_atremains unchanged.Reacted by Javier Soques, Sheldenburg and Graeme HollidayHere is my very rough example code:
import time from datetime import datetime from typing import Optional from sqlalchemy import Column, DateTime, func from sqlmodel import Field, Session, SQLModel, create_engine, select class Model(SQLModel, table=True): id: Optional[int] = Field(default=None, primary_key=True) foo: Optional[str] created_at: Optional[datetime] = Field( sa_column=Column(DateTime(timezone=True), server_default=func.now()) ) updated_at: Optional[datetime] = Field( sa_column=Column(DateTime(timezone=True), onupdate=func.now()) ) sqlite_file_name = "database.db" sqlite_url = f"sqlite:///{sqlite_file_name}" engine = create_engine(sqlite_url) def create_db_and_tables(): SQLModel.metadata.create_all(engine) def create_entry(): with Session(engine) as session: m = Model() print(f"created {m=}") session.add(m) session.commit() session.refresh(m) print(f"added and refreshed {m=}") def update_entry(): with Session(engine) as session: s = select(Model) m = session.exec(s).first() print(f"\nfound {m=}") m.foo = "bar" print(f"modified {m=}") session.add(m) session.commit() session.refresh(m) print(f"refreshed {m=}") def main(): create_db_and_tables() create_entry() time.sleep(5) update_entry() if __name__ == "__main__": main()
Running it outputs:
created m=Model(id=None, foo=None, created_at=None, updated_at=None) added and refreshed m=Model(foo=None, created_at=datetime.datetime(2022, 6, 29, 8, 14, 53), updated_at=None, id=1) found m=Model(foo=None, created_at=datetime.datetime(2022, 6, 29, 8, 14, 53), updated_at=None, id=1) modified m=Model(foo='bar', created_at=datetime.datetime(2022, 6, 29, 8, 14, 53), updated_at=None, id=1) refreshed m=Model(foo='bar', created_at=datetime.datetime(2022, 6, 29, 8, 14, 53), updated_at=datetime.datetime(2022, 6, 29, 8, 14, 58), id=1)
So
created_atis constant, andupdate_atis 5 seconds aftercreated_atas expected given the 5 second sleep between creation and update.Reacted by Junior, ronald-das, Paolo Dina, Johan Almquist, Ben Falk, FroggyBrid, sean huang and Amy Chen@RobertRosca This example is very detailed! thanks a lot!
Thanks! Happy it helped 😄
I wrote up an explanation and created PR #372 to add this to the documentation, since it does come up pretty often.
@RobertRosca This is really helpful but there is an issue with
created_atfield. datetime on created_at is fixed for every resource creation.server_defaultassigns default data directly to the table when using alembic.So when using the example code I showed with Alembic instead of
SQLModel.metadata.create_allthecreated_atfield always has the same value, as if the default value were set to a constant datetime?I haven't tested it with Alembic, but their docs show that the
server_default=func.now()should work to set the time to the current time for a timestamp column:from alembic import op from sqlalchemy import Column, TIMESTAMP, func # specify "DEFAULT NOW" along with the column add op.add_column('account', Column('timestamp', TIMESTAMP, server_default=func.now()) )
I guess there could be some issue with interactions between Alembic, SQLAlchemy, and SQLModel causing the default to be a constant instead of the now function, but I haven't had time to look.
Since this should be supported by Alembic then if this isn't working correctly it's probably an issue in SQLModel, so I'd say open an issue here with some example code. I'll try and have a look some time this week as well, but maybe somebody else would be able to help before I can 😄
Thanks a lot for the help here @RobertRosca ! 🍰
And thanks @regainOWO for coming back to close the issue. ☕
I don't understand... this definitely does not work for me.
I have a database containing some users, when I add the columncreated_atand executealembic upgrade headI get this error:sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) Cannot add a column with non-constant default [SQL: ALTER TABLE users ADD COLUMN created_at DATETIME DEFAULT (CURRENT_TIMESTAMP)]migration script:
def upgrade() -> None: # ### commands auto generated by Alembic - please adjust! ### op.add_column('users', sa.Column('created_at', sa.DateTime(timezone=True), server_default=sa.text('(CURRENT_TIMESTAMP)'), nullable=True)) # ### end Alembic commands ### def downgrade() -> None: # ### commands auto generated by Alembic - please adjust! ### op.drop_column('users', 'created_at') # ### end Alembic commands ###
I just added this line to
Userstable:created_at: Optional[datetime.datetime] = Field( sa_column=Column(DateTime(timezone=True), server_default=func.now()) )
I figured out this works:
I added these lines toUsertable:created_at: datetime.datetime = Field( default_factory=datetime.datetime.utcnow, nullable=False, )
In
env.pyI added the argumentrender_as_batch=Truetocontext.configure.
I autogenerated the migration.
I changed theupgradefunction to add thecreated_atcolumn with nullable=True, I updated the values withsa.func.nowand then Ibatch_alter_tableto make it nullable=False.def upgrade() -> None: # ### commands auto generated by Alembic - please adjust! ### print("Adding column created_at") op.add_column("users", sa.Column("created_at", sa.DateTime(), nullable=True)) # Get the users.created_at column user = sa.sql.table( "users", sa.sql.column("created_at", sa.DateTime()), ) # Update the users.created_at column op.execute(user.update().values(created_at=sa.func.now())) with op.batch_alter_table("users", schema=None) as batch_op: # Set the users.created_at column to not null batch_op.alter_column("created_at", nullable=False) # ### end Alembic commands ### def downgrade() -> None: # ### commands auto generated by Alembic - please adjust! ### with op.batch_alter_table("users", schema=None) as batch_op: batch_op.drop_column("created_at")
I also implemented
updated_atfield here with the following:
Add this to the yourSQLModel:updated_at: Optional[datetime.datetime] = Field( sa_column=Column(DateTime(), onupdate=func.now()) )
Alembic migration:
def upgrade() -> None: op.add_column("users", sa.Column("updated_at", sa.DateTime(), nullable=True)) def downgrade() -> None: op.drop_column("users", "updated_at")
Or in case you are using batch operation:
def upgrade() -> None: with op.batch_alter_table('users', schema=None) as batch_op: batch_op.add_column(sa.Column('updated_at', sa.DateTime(), nullable=True)) def downgrade() -> None: with op.batch_alter_table('users', schema=None) as batch_op: batch_op.drop_column('updated_at')
Reacted by sean huangThis doesn't work if I factor out a field with
sa_columnattribute to another class and inherit from it, like:class WithId(SQLModel): """ Database row with ID field """ id: UUID = Field(default_factory=lambda: ULID().to_uuid(), description='Row ULID', primary_key=True) class TimedRow(SQLModel): """ Database row with status times """ created: datetime = Field( default_factory=lambda: datetime.now(tz=config.timezone), sa_column=Column(DateTime(timezone=True), server_default=text('CURRENT_TIMESTAMP'), nullable=False), description='Time when row was created', ) updated: datetime | None = Field( sa_column=Column(DateTime(timezone=True)), description='Time when row was last updated', ) deleted: datetime | None = Field( sa_column=Column(DateTime(timezone=True)), description='Time when row was deleted', ) class Practice(TimedRow, WithId, table=True): name: str
If I have definitions like
Practicein more than one module, I get:sqlalchemy.exc.ArgumentError: Column object 'created' already assigned to Table '<tablename>'on the second and following import of such a module.
Reacted by Adrian Obelmejias and Matthias Harzer
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Example Code
Description
when i create a Image_Save_Record instance and commit it to db, the create_time field value should be that system time current.
when i change the Image_Save_Record instance which i created before and commit it to db, the update_time field value should be that system time current.
Is there sqlmodel have option to do the same like this?
Operating System
Windows
Operating System Details
No response
SQLModel Version
0.0.6
Python Version
3.7.9
Additional Context
No response