Upgrade Instructions

Upgrade from 3.x to 4.x

If you are customizing the error messages of the following built-in validation rules, you may need to change the parameter placeholders from %v to the Go template variable placeholders.

• Length: use {{.min}} and {{.max}} in the error message to refer to the minimum and maximum lengths.
• Min: use {{.threshold}} in the error message to refer to the lower bound.
• Max: use {{.threshold}} in the error message to refer to the upper bound
• MultipleOf: use {{.base}} in the error message to refer to the base of the multiples.

For example, `go // 3.x lengthRule := validation.Length(2,10).Error("the length must be between %v and %v")

// 4.x lengthRule := validation.Length(2,10).Error("the length must be between {{.min}} and {{.max}}")

## Upgrade from 2.x to 3.x

* Instead of using `StructRules` to define struct validation rules, use `ValidateStruct()` to declare and perform
  struct validation. The following code snippet shows how to modify your code:
```go
// 2.x usage
err := validation.StructRules{}.
	Add("Street", validation.Required, validation.Length(5, 50)).
	Add("City", validation.Required, validation.Length(5, 50)).
	Add("State", validation.Required, validation.Match(regexp.MustCompile("^[A-Z]{2}$"))).
	Add("Zip", validation.Required, validation.Match(regexp.MustCompile("^[0-9]{5}$"))).
	Validate(a)

// 3.x usage
err := validation.ValidateStruct(&a,
	validation.Field(&a.Street, validation.Required, validation.Length(5, 50)),
	validation.Field(&a.City, validation.Required, validation.Length(5, 50)),
	validation.Field(&a.State, validation.Required, validation.Match(regexp.MustCompile("^[A-Z]{2}$"))),
	validation.Field(&a.Zip, validation.Required, validation.Match(regexp.MustCompile("^[0-9]{5}$"))),
)

• Instead of using Rules to declare a rule list and use it to validate a value, call Validate() with the rules directly.

data := "example"

// 2.x usage
rules := validation.Rules{
	validation.Required,      
	validation.Length(5, 100),
	is.URL,                   
}
err := rules.Validate(data)

// 3.x usage
err := validation.Validate(data,
	validation.Required,      
	validation.Length(5, 100),
	is.URL,                   
)

• The default struct tags used for determining error keys is changed from validation to json. You may modify

validation.ErrorTag to change it back.