💯Go Struct and Field validation, including Cross Field, Cross Struct, Map, Slice and Array diving
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validator/doc.go

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/*
Package validator implements value validations for structs and individual fields based on tags.
Built In Validator
myValidator = validator.New("validate", validator.BakedInFunctions)
errs := myValidator.ValidateStruct(//your struct)
valErr := myValidator.ValidateFieldByTag(field, "omitempty,min=1,max=10")
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 := myValidator.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 error 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(top interface{}, current interface{}, field interface{}, param string) bool {
if whatever {
return false
}
return true
}
myValidator.AddFunction("custom tag name", customFunc)
// NOTES: using the same tag name as an existing function
// will overwrite the existing one
Cross Field Validation
Cross Field Validation can be implemented, for example Start & End Date range validation
// NOTE: when calling myValidator.validateStruct(val) val will be the top level struct passed
// into the function
// when calling myValidator.ValidateFieldByTagAndValue(val, field, tag) val will be
// whatever you pass, struct, field...
// when calling myValidator.ValidateFieldByTag(field, tag) val will be nil
//
// Because of the specific requirements and field names within each persons project that
// uses this library it is likely that custom functions will need to be created.
// however there are some build in Generic Cross Field validation, see Baked In Validators and
// Tags below
func isDateRangeValid(val interface{}, field interface{}, param string) bool {
myStruct := val.(myStructType)
if myStruct.Start.After(field.(time.Time)) {
return false
}
return true
}
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
NOTE: Baked In Cross field validation only compares fields on the same struct,
if cross field + cross struct validation is needed your own custom validator
should be implemented.
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)
structonly
When a field that is a nest struct in encountered and contains this flag
any validation on the nested struct such as "required" will be run, but
none of the nested struct fields will be validated. This is usefull if
inside of you program you know the struct will be valid, but need to
verify it has been assigned.
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)
For time.Time ensures the time value is greater than time.Now.UTC()
(Usage: gt)
gte
Same as 'min' above. Kept both to make terminology with 'len' easier
(Usage: gte=10)
For time.Time ensures the time value is greater than or equal to time.Now.UTC()
(Usage: gte)
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)
For time.Time ensures the time value is less than time.Now.UTC()
(Usage: lt)
lte
Same as 'max' above. Kept both to make terminology with 'len' easier
(Usage: lte=10)
For time.Time ensures the time value is less than or equal to time.Now.UTC()
(Usage: lte)
gtfield
Only valid for Numbers and time.Time types, this will validate the field value
against another fields value either within a struct or passed in field.
usage examples are for validation of a Start and End date:
Validation on End field using ValidateByStruct Usage(gtfield=Start)
Validating by field ValidateFieldByTagAndValue(start, end, "gtfield")
gtefield
Only valid for Numbers and time.Time types, this will validate the field value
against another fields value either within a struct or passed in field.
usage examples are for validation of a Start and End date:
Validation on End field using ValidateByStruct Usage(gtefield=Start)
Validating by field ValidateFieldByTagAndValue(start, end, "gtefield")
ltfield
Only valid for Numbers and time.Time types, this will validate the field value
against another fields value either within a struct or passed in field.
usage examples are for validation of a Start and End date:
Validation on End field using ValidateByStruct Usage(ltfield=Start)
Validating by field ValidateFieldByTagAndValue(start, end, "ltfield")
ltefield
Only valid for Numbers and time.Time types, this will validate the field value
against another fields value either within a struct or passed in field.
usage examples are for validation of a Start and End date:
Validation on End field using ValidateByStruct Usage(ltefield=Start)
Validating by field ValidateFieldByTagAndValue(start, end, "ltefield")
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"
}
myValidator.ValidateStruct(t) // this will panic
*/
package validator