validator

Overview ¶

Package validator implements value validations for structs and individual fields based on tags.

Built In Validator ¶

The package contains a built in Validator instance for use, but you may also create a new instance if needed.

// built in
errs := validator.ValidateStruct(//your struct)
valErr := validator.ValidateFieldByTag(field, "omitempty,min=1,max=10")

// new
newValidator = validator.New("struct tag name", validator.BakedInFunctions)

A simple example usage:

type UserDetail {
	Details string `validate:"-"`
}

type User struct {
	Name         string     `validate:"required,max=60"`
	PreferedName string     `validate:"omitempty,max=60"`
	Sub          UserDetail
}

user := &User {
	Name: "",
}

// errs will contain a hierarchical list of errors
// using the StructValidationErrors struct
// or nil if no errors exist
errs := validator.ValidateStruct(user)

// in this case 1 error Name is required
errs.Struct will be "User"
errs.StructErrors will be empty <-- fields that were structs
errs.Errors will have 1 error of type FieldValidationError

Error Handling ¶

The error can be used like so

fieldErr, _ := errs["Name"]
fieldErr.Field    // "Name"
fieldErr.ErrorTag // "required"

Both StructValidationErrors and FieldValidationError implement the Error interface but it's intended use is for development + debugging, not a production error message.

fieldErr.Error() // Field validation for "Name" failed on the "required" tag
errs.Error()
// Struct: User
// Field validation for "Name" failed on the "required" tag

Why not a better error message? because this library intends for you to handle your own error messages

Why should I handle my own errors? Many reasons, for me building an internationalized application I needed to know the field and what validation failed so that I could provide an error in the users specific language.

if fieldErr.Field == "Name" {
	switch fieldErr.ErrorTag
	case "required":
		return "Translated string based on field + error"
	default:
	return "Translated string based on field"
}

The hierarchical structure is hard to work with sometimes.. Agreed Flatten function to the rescue! Flatten will return a map of FieldValidationError's but the field name will be namespaced.

// if UserDetail Details field failed validation
Field will be "Sub.Details"

// for Name
Field will be "Name"

Custom Functions ¶

Custom functions can be added

//Structure
func customFunc(field interface{}, param string) bool {

	if whatever {
		return false
	}

	return true
}

validator.AddFunction("custom tag name", customFunc)
// NOTE: using the same tag name as an existing function
//       will overwrite the existing one

Custom Tag Name ¶

A custom tag name can be set to avoid conficts, or just have a shorter name

validator.SetTag("valid")

Multiple Validators ¶

Multiple validators on a field will process in the order defined

type Test struct {
	Field `validate:"max=10,min=1"`
}

// max will be checked then min

Bad Validator definitions are not handled by the library

type Test struct {
	Field `validate:"min=10,max=0"`
}

// this definition of min max will never validate

Baked In Validators and Tags ¶

Here is a list of the current built in validators:

-
	Tells the validation to skip this struct field; this is particularily
	handy in ignoring embedded structs from being validated. (Usage: -)

|
	This is the 'or' operator allowing multiple validators to be used and
	accepted. (Usage: rbg|rgba) <-- this would allow either rgb or rgba
	colors to be accepted. This can also be combined with 'and' for example
	( Usage: omitempty,rgb|rgba)

omitempty
	Allows conitional validation, for example if a field is not set with
	a value (Determined by the required validator) then other validation
	such as min or max won't run, but if a value is set validation will run.
	(Usage: omitempty)

required
	This validates that the value is not the data types default value.
	For numbers ensures value is not zero. For strings ensures value is
	not "". For slices, arrays, and maps, ensures the length is not zero.
	(Usage: required)

len
	For numbers, max will ensure that the value is
	equal to the parameter given. For strings, it checks that
	the string length is exactly that number of characters. For slices,
	arrays, and maps, validates the number of items. (Usage: len=10)

max
	For numbers, max will ensure that the value is
	less than or equal to the parameter given. For strings, it checks
	that the string length is at most that number of characters. For
	slices, arrays, and maps, validates the number of items. (Usage: max=10)

min
	For numbers, min will ensure that the value is
	greater or equal to the parameter given. For strings, it checks that
	the string length is at least that number of characters. For slices,
	arrays, and maps, validates the number of items. (Usage: min=10)

gt
	For numbers, this will ensure that the value is greater than the
	parameter given. For strings, it checks that the string length
	is greater than that number of characters. For slices, arrays
	and maps it validates the number of items. (Usage: gt=10)

gte
	Same as 'min' above. Kept both to make terminology with 'len' easier
	(Usage: gte=10)

lt
	For numbers, this will ensure that the value is
	less than the parameter given. For strings, it checks
	that the string length is less than that number of characters.
	For slices, arrays, and maps it validates the number of items.
	(Usage: lt=10)

lte
	Same as 'max' above. Kept both to make terminology with 'len' easier
	(Usage: lte=10)

alpha
	This validates that a strings value contains alpha characters only
	(Usage: alpha)

alphanum
	This validates that a strings value contains alphanumeric characters only
	(Usage: alphanum)

numeric
	This validates that a strings value contains a basic numeric value.
	basic excludes exponents etc...
	(Usage: numeric)

hexadecimal
	This validates that a strings value contains a valid hexadecimal.
	(Usage: hexadecimal)

hexcolor
	This validates that a strings value contains a valid hex color including
	hashtag (#)
	(Usage: hexcolor)

rgb
	This validates that a strings value contains a valid rgb color
	(Usage: rgb)

rgba
	This validates that a strings value contains a valid rgba color
	(Usage: rgba)

hsl
	This validates that a strings value contains a valid hsl color
	(Usage: hsl)

hsla
	This validates that a strings value contains a valid hsla color
	(Usage: hsla)

email
	This validates that a strings value contains a valid email
	This may not conform to all possibilities of any rfc standard, but neither
	does any email provider accept all posibilities...
	(Usage: email)
url
	This validates that a strings value contains a valid url
	This will accept any url the golang request uri accepts but must contain
	a schema for example http:// or rtmp://
	(Usage: url)
uri
	This validates that a strings value contains a valid uri
	This will accept any uri the golang request uri accepts (Usage: uri)

Validator notes:

regex
	a regex validator won't be added because commas and = signs can be part of
	a regex which conflict with the validation definitions, although workarounds
	can be made, they take away from using pure regex's. Furthermore it's quick
	and dirty but the regex's become harder to maintain and are not reusable, so
	it's as much as a programming philosiphy as anything.

	In place of this new validator functions should be created; a regex can be
	used within the validator function and even be precompiled for better efficiency.

	And the best reason, you can sumit a pull request and we can keep on adding to the
	validation library of this package!

Panics ¶

This package panics when bad input is provided, this is by design, bad code like that should not make it to production.

type Test struct {
	TestField string `validate:"nonexistantfunction=1"`
}

t := &Test{
	TestField: "Test"
}

validator.ValidateStruct(t) // this will panic