Define your validation schema inline

Posted on by

The TurboGears docs show how to assign validators for individual parameters in the validate decorator like this:

@validate(validators={'a':validators.Int(), 'b':validators.DateConverter()})
@error_handler()
def f(self, a, b, tg_errors=None):
# Now a is already an integer and b is already a datetime.date object,
# unless there were some validation errors.

That’s great, but there are some validations that depend on numerous parameters at the same time. For example, you might want to make sure that an employee’s hire date precedes the termination date.

I already knew how to subclass validators.Schema to do this, and then pass that instance into the validate decorator like this:

class MattSchema(validators.Schema):
a = validators.Int()
b = validators.DateConverter()
chained_validators = [blah] # pretend that blah does some compound validation.

@validate(validators=MattSchema())
def f(self, a, b)

This approach is fine, but today I discovered that it is also possible to define a Schema inline, inside the validate decorator, and specify the chained_validators right there, like this:

@expose('.templates.shiftreports.overtime')
@validate(validators=validators.Schema(
a=validators.Int(),
dt=validators.DateConverter(),
chained_validators=[blah]),
state_factory=matt_state_factory)
def f(self, a, b):

What’s the point? Well, it seems wasteful to define a class and hide it in another file if that schema is only going to be used for exactly one controller. Also, this makes it really fast for me to mix and match comound validators with controllers. I don’t need to pop open my separate validators file where all my elaborate schemas live. I can define them right here.

I’m very forgetful too, so I like to keep my code shallow so that I can instantly see what the heck something does. With all the validators right there, I can easily figure out what the system intends to do.

However, I would define a Schema subclass as soon as I see that I need the same thing twice.

I’m happy that the FormEncode authors had the foresight to support this inline approach along with the declarative style.

30 thoughts on “Define your validation schema inline”

  3. Thanks for the post I liked reading it, keep posting interesting stuff like this coming!

    Lisa

  5. Thanks for explaining by means of giving code..Very useful and good post..I will try this and post my further comments here..

  8. I just wanted to document it so that I wouldn't forget how. Yeah, I
    agree that defining things inline is usually not ideal. It isn't easy
    to test or reuse the code. There are sometimes moments when it is
    useful though. It is nice to see everything all in one place.

  10. Declarative style is more appropriate and much easy to understand. Thank you for giving us some insights about schema.

  15. There are sometimes moments when it is useful though. It is nice to see everything all in one place. However, I would define a Schema subclass as soon as I see that I need the same thing twice.

    Thanks

  16. I’m very forgetful too, so I like to keep my code shallow so that I can instantly see what the heck something does. With all the validators right there, I can easily figure out what the system intends to do.

  22. I just wanted to document it so that I wouldn't forget how. Yeah, I
    agree that defining things inline is usually not ideal. It isn't easy
    to test or reuse the code. There are sometimes moments when it is
    useful though. It is nice to see everything all in one place.

  29. This article gives the light in which we can observe the reality. this is very nice one and gives in depth information. thanks for this nice article Good post…..Valuable information for all.I will recommend my friends to read this for sure

    Thanks
    Kane
    ______________________________________________
    british heart foundation diet | cayenne pepper detox | diets for quick weight loss | easy diet plans | maple syrup detox | miracle cabbage soup diet | sugar busters diet | weight gain diets | british heart foundation diet | cayenne pepper detox | diets for quick weight loss | easy diet plans | maple syrup detox | sugar busters diet | weight gain diets | miracle cabbage soup diet

  30. Also, this makes it really fast for me to mix and match comound validators with controllers. I don’t need to pop open my separate validators file where all my elaborate schemas live. I can define them right here.

Comments are closed.