validator treat json.Number as string

[Tevic]

Package version eg. v8, v9:

v10

Issue, Question or Enhancement:

validator treat json.Number as string

Code sample, to showcase or reproduce:

package main

import (
    "encoding/json"
    "fmt"

    "github.com/go-playground/validator/v10"
)

type Test struct {
    Val json.Number `validate:"min=20"`
}

func main() {
    validate := validator.New()
    test := Test{
        Val: "100",
    }
    fmt.Println(validate.Struct(test))
}


Output:
Key: 'Test.Val' Error:Field validation for 'Val' failed on the 'min' tag
Expect:
No Error

I know json.Number is string,but if we define a type as json.Number,we prefer this value act as a number value, so is there any way to let validator behavior act as number too?

[elias19r]

Hi @Tevic

Yes, I think there is a way to let the validator act as a numeric value for encoding/json.Number

I've implemented it in PR https://github.com/go-playground/validator/pull/634

I'm not very knowledgeable about this codebase yet, but as encoding/json.Number's underlying type is string, I think that creating a special case for string validations would make sense

Let's wait for maintainers to review it

[deankarn]

Hey @Tevic @elias19r

As much as I'd like to merge that PR json.Number is in fact a string and not a number as so I'm hesitant to add this special case because:

1. It may be a breaking change for those relying on it validating as a string already.
2. Treating this type as a special case would open up the door for every other type of special case and it's a door I don't want to open.

Having said that, this sort of thing has been thought of and there are 3 options for dealing with this sort of thing from least to most recommended:

1. Create a struct validation to handle this specific case if it's a one-off.
2. Create a custom validation that converts the value to an int for the validation.
3. Register a Custom Type Func. this is specifically designed to do what you want by converting the type to a different one prior to doing any validation. Here is an example of your use case: https://play.golang.org/p/MS_Dv4Nr3CE

Please let me know if this helps :)