schema: combining constrained with other predicates

[Bruno Bonacci]

Hi,

I'm extending schema to cover some common validations in my dataset,

and I'm trying to combine standard predicates with some custom one.

One example could be to validate that a value is a string and that isn't longer than a certain size.

My predicate look as follow:

 

(defn max-length

  [max-size]

  (s/pred (fn [s] (>= max-size (count s)))

          (str "max-length[" max-size "]")))

 

(s/validate (s/both s/Str (max-length 5)) "hello")

;;=> "hello"

 

(s/validate (s/both s/Str (max-length 5)) "hello!")

;;=> ExceptionInfo Value does not match schema: (not ("max-length[5]" "hello!"))

 

 

Now  both is deprecated in favour of constrained. However constrain doesn't accept predicated but just functions:

 

(s/validate (s/constrained s/Str (max-length 5)) "hello")

;;=> Not a function: schema.core.Predicate@b79b020b

 

If I turn the max-length predicate into a simple function it works but the errors messages are useless:

 

(defn max-length2

  [max-size]

  (fn [s] (>= max-size (count s))))

 

(s/validate (s/constrained s/Str (max-length2 5)) "hello!")

;;=> Value does not match schema: (not (user$max-length2/fn--23140 "hello!"))

 

 

Is there any reason why constrained doesn't accept predicates? 

Do you guys have any suggestion on how to improve this scenario?

Thanks

Bruno

[Jason Wolfe]

Hi Bruno,

Thanks for the detailed question. Constrained takes a third argument with predicate name. Or you can just give the predicate function a name.  Is that what you're looking for?

Best,
Jason

[Bruno Bonacci]

Hi Jason,

thanks for the quick reply.

I've seen the predicate name in constrained but that one is for the whole predicate which it doesn't tell you much 

about which of the individual constrained failed. consider

 

  (s/constrained s/Int is-fib? is-square? is-prime? "complex constraint")

 

 

the error will be something like:

 

  ;;=> ExceptionInfo Value does not match schema: (not ("complex constraint" 76))

 

 

but you don't have any clue which of the predicate function failed.

Bruno

[Jason Wolfe]

s/constrained only takes a single predicate.  If you want multiple constraints, you can wrap multiple times.  

(s/constrained (s/constrained s/Int is-fib?) is-square?).

Best,

Jason