Validation with multiple fields

[ramalhoruben]

Is it possible to validate a field using information from a second field? For example to check if the object doesn't violate a compound key constraint? Here's an example of what I pretend to do:

def ClientExists(v):

    if client_exists(v):
        return v
    else:
        raise Invalid('Client does not exist')

def CodeIsValid(v):
    # Check if (client_id, fraction_code) is unique

sch_addfraction = Schema({
    Required('client_id') : All(Coerce(int), Range(min=1, max=10000), ClientExists),
    Required('fraction_code') : All(str, Length(min=1, max=4), CodeIsValid),
})

[tusharmakkar08]

Hey @ramalhoruben

I think it's not currently possible.

@alecthomas: What are your views on supporting these kind of constraints?

Thanks.

[alecthomas]

I think we should support a way of validating the parent object.

[nbob]

@alecthomas is it possible to pass to validator function entire data object as a second argument?

[erik-stephens]

Will partial function application work?

from functools import partial

def CodeIsValid(client_id, v):
    # Check if (client_id, fraction_code) is unique

sch_addfraction = Schema({
    Required('client_id') : All(Coerce(int), Range(min=1, max=10000), ClientExists),
    Required('fraction_code') : All(str, Length(min=1, max=4), partial(CodeIsValid, getClientId())),
})

Might get a bit cumbersome/verbose for more complicated use cases but it helps keep voluptuous simple.

[bruce-szalwinski]

One solution is given in #124.