Defaults/calculated fields

[joshowen]

And only calculate defaults if they aren't set already.

We've found this very helpful, let me know what you guys think. Obviously it requires some documentation.

[joshowen]

We've been using this as follows:

class Position(pynamodb.models.Model):
    portfolio_id = NumberAttribute()
    position_date = DateAttribute()
    status = NumberAttribute(null=True)
    portfolio_date = BinaryAttribute(hash_key=True, default=lambda x: to_dated_attribute(x.position_date, x.portfolio_id))
    most_current = BooleanAttribute(null=True, calculator=lambda x: x.status == PositionStatus.MOST_CURRENT.value or None)

By encapsulating this logic in the model, we've been able to simplify a lot of our Position creation code.

• most_current is calculated on every object save
• portfolio_date is calculated at object creation

[joshowen]

@jlafon any thoughts

[jlafon]

@joshowen That really makes for succinct code! Can we add some tests?

[pappacena]

+1

[joshowen]

I'll try to add some tests this week or next.

[garrettheel]

Reopening with new default branch