Go-Validators

Go-Validators is a library written in Go allowing to validate any field of a struct.

Usage

Basic

// define a public object to validate
type ObjectToBeValidated struct {
    First string
    Second int
    Third *bool
}

// validators definition function
// the object passed as parameter needs to be a pointer
func getValidators(object *ObjectToBeValidated) []validators.Validator {
	return []validators.Validator{
        validators.String(object, "first").
            Default("fallback").
            OneOf("fallback", "valid"),
        validators.Int(object, "second").
            Gt(1).
            Lte(10),
        validators.Pointer(object, "third", func(field, value bool) validators.Validator {
            return validators.BoolFromValue(field, value).Equal("true")
        })}
}

func main() {
    third := true
    o := ObjectToBeValidated{
        First: "any value", // nok
        Second: 3, // ok
        Third: &third // ok
    }

    // validation step
    if err := validators.Validate(getValidators(&o)); err != nil {
        panic(err)
    }

    ...
}

Conditional

It is also possible to create conditional validation statements with Or and And functions.

You can use them in the following way:

func validate(object *ObjectToBeValidated) []validators.Validator {
	return []validators.Validator{
		validators.Or(
			validators.And(
				validators.String(object, "first").Equal("first"),
                validators.Int(object, "second").Equal(2),
			),
			validators.And(
				validators.String(object, "first").Equal("first"),
                validators.Int(object, "second").Equal(2),
			),
		),
	}
}

And is simple syntactic sugar that becomes useful when dealing with complex validations. It is not mandatory as it is the default validation behavior.

Rules

There are a few rules that are worth to notice:

• Implementation impose validated to be exposed publicly (must start with a capital letter). This is particularly important when using the Default method as it will update the input object and that will only work if it is a pointer
• Parameters in validators.String or validators.Int or any other validator factories are:
  1. the address of the object to be validated
  2. the name of the field to validate (case insensitive) as a string

Besides, primitive types, there are also validators for time.Time, maps, slices, emails (and pointers).

You will find below the validation methods by data type:

Strings

• Equal
• NotEqual
• IsNotZeroValue
• IsZeroValue
• OneOf
• Default
• UpdateBeforeValidation
• MatchRegex
• Contains
• DoesNotContain
• StartsWith
• DoesNotStartWith
• EndsWith
• DoesNotEndWith
• MaxSize
• MinSize
• MinMaxSize

Ints

• Equal
• NotEqual
• IsNotZeroValue
• IsZeroValue
• OneOf
• Default
• UpdateBeforeValidation
• Gt
• Lt
• Gte
• Lte

Floats

• Equal
• NotEqual
• IsNotZeroValue
• IsZeroValue
• OneOf
• Default
• UpdateBeforeValidation
• Gt
• Lt
• Gte
• Lte

Bools

• Equal
• NotEqual
• IsNotZeroValue
• IsZeroValue
• OneOf
• Default
• UpdateBeforeValidation

time.Time

• After
• Before
• Equal
• NotEqual
• IsNotZeroValue
• IsZeroValue
• OneOf
• Default
• UpdateBeforeValidation

Maps

• ContainsKey
• ContainsValue
• DoesNotContainKey
• DoesNotContainValue
• Default
• UpdateBeforeValidation
• MaxSize
• MinSize
• MinMaxSize

Slices

• Contains
• DoesNotContain
• Default
• UpdateBeforeValidation
• MaxSize
• MinSize
• MinMaxSize

Pointers

• IsDefined
• IsNotDefined
• Default
• UpdateBeforeValidation

It is also possible to validate the value addressed by the pointer (see previous example).

Emails

• Equal
• NotEqual
• IsNotZeroValue
• IsZeroValue
• OneOf
• Default
• UpdateBeforeValidation
• MatchRegex
• Contains
• DoesNotContain
• StartsWith
• DoesNotStartWith
• EndsWith
• DoesNotEndWith
• MaxSize
• MinSize
• MinMaxSize
• IsValid