Implementing Timestamped Models in PeeWee

April 15, 2015

date_created and date_updated (or variations of the same) are important fields for any table. date_created to show when a record was created, date_updated to show when it was last updated. They are invaluable, especially for audit logs.

I’ve been using PeeWee, a lightweight Python ORM, for a small project at work. Since I’m using SQLite3 for the project, I decided to use the ORM to ease the database access work. This post will show how I implemented a Timestamped Model.

The rules for my timestamped model are:

• Set date_created field to current timestamp any time a record is created
• Set date_updated field to current timestamp any time a record is updated

I have a BaseModel from which all my PeeWee models inherit

database = SqliteDatabase(Config.get("DATABASE"), **{})

class BaseModel(Model):
    class Meta:
        database = database

Then my TimestampedModel inherits from the BaseModel:

class TimestampedModel(BaseModel):
    def save(self, *args, **kwargs):
        if self._get_pk_value() is None:
            # this is a create operation, set the date_created field
            self.date_created = datetime.datetime.now().strftime(
                "%Y-%m-%d %H:%M:%S")
        self.date_updated = datetime.datetime.now().strftime(
            "%Y-%m-%d %H:%M:%S")
        return super(TimestampedModel, self).save(*args, **kwargs)

In the snippet above, I’ve overridden the save method to do my “timestamping”. I found the _get_pk_value() in the source code (go open source!).

Then in my model, I just inherit from the TimestampedModel:

class Person(TimestampedModel):
    date_created = DateTimeField()
    date_updated = DateTimeField()

    # other cool fields

An alternative, especially for the date_created field, would have been to have a default value in the model, i.e. something like:

class Person(BaseModel):
    date_created = DateTimeField(default=datetime.datetime.now().strftime(
        "%Y-%m-%d %H:%M:%S"))

However, I noticed that for create operations that were close together, e.g. a few seconds apart, they were being given the same date_created value. I’m not sure if I was doing something wrong, but the solution above resolved this issue for me.

Of course, using the SQL triggers (e.g. ON CREATE CURRENT_TIMESTAMP) would also work (especially for MySQL). For SQLite however, you run into issues when writing tests and you want to use the memory for temporary storage. You might get value missing errors for columns that are NOT NULL, since the SQL schema isn’t used when accessing the database from within the tests.

Check out this Gist for a complete example.

I hope this helps someone out there! All the best!

– Back to code!

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