Brilliant - thank you very much for the thoughtful reply.
I actually set it as a session var bc there are several tables with a
decimal field that I want to be consistent with each other, BUT I really
appreciate your point about accidentally triggering db migrations. I hadn't
considered that.
-jl
On Thursday, December 28, 2017 at 3:18:41 PM UTC-7, Anthony wrote:
>
> On Thursday, December 28, 2017 at 11:22:25 AM UTC-5, Jordan Ladora wrote:
>>
>> Hi,
>>
>> I'm using postgres and have a table-
>>
>> db.define_table('volumes',
>> Field('vol', 'decimal(100, session.decplaces)', default=0,
>> readable=False, writable=False),
>> auth.signature, migrate=True,
>> )
>>
>
> Notice that 'decimal(100, session.decplaces)' is a string literal, not
> Python code calling a decimal() function. The string literal is parsed by
> the DAL, extracting the strings "100" and "session.decplaces", expecting
> each to be interpretable as an integer. Of course, the string
> "session.decplaces" is not an integer, so you get an error. Instead, you
> have to create a string that includes the relevant integer value:
>
> 'decimal(100, %s)' % session.decplaces
>
> which will ultimately generate the string:
>
> 'decimal(100, 7)'
>
> Generally, though, storing the number of decimal places in a session
> variable is probably not a good idea. Presumably you are using the session
> because you want to allow different user sessions to have different numbers
> of decimal places. But that doesn't work because the decimal places can
> affect the database schema (depending on the database) -- so every time a
> different user makes a request, you'll end up running a database migration
> if migrations are turned on, or otherwise there will be no point to
> specifying the different decimal places if migrations are turned off. In
> any case, you will not end up with custom decimal places for each user, as
> the decimal places are defined for an entire column, not per row. Pick one
> decimal place and use it for all users (which means there is no reason to
> store it in the session).
>
> Anthony
>
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