Golang parameter validation, which can replace go-playground/validator, includes ncluding Cross Field, Map, Slice and Array diving, provides readable,flexible, configurable validation.



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Checker is a parameter validation package, can be use in struct/non-struct validation, including cross field validation in struct, elements validation in Slice/Array/Map, and provides customized validation rule.


Go 1.13 or above.


go get -u github.com/liangyaopei/checker


When use Add to add rule,fieldExpr has three situations:

  • fieldExpr is empty,validate the value directly.
  • fieldExpr is single field,fetch value in struct, then validate.
  • fieldExpr is string separated by ., fetch value in struct according hierarchy of struct, then validate.

When fetching value by fieldExpr, if the field is pointer, it will fetch the underlying value of pointer to validate; if the field is nil pointer, it failed validation rule.

For special use of validating nil pointer, Nil rule can be used.

example from checker_test.go

// Item.Email is the format of email address
type Item struct {
	Info  typeInfo
	Email string

type typeStr string
// Item.Info.Type = "range",typeInfo.Type 's length is 2,elements with format of "2006-01-02"
// Item.Info.Type = "last",typeInfo.Type 'is length is 1,elements is positive integer,Granularity is one of day/week/month
type typeInfo struct {
	Type        typeStr
	Range       []string
	Unit        string
	Granularity string

// rules are as follow
rule := And(
					EqStr("Type", "range"),
					Length("Range", 2, 2),
					Array("Range", isDatetime("", "2006-01-02")),
					EqStr("Type", "last"),
					InStr("Granularity", "day", "week", "month"),
itemChecker := NewChecker()
// validate parameter
itemChecker.Add(rule, "wrong item")

rule variable in above code constructs a rule tree. rule tree

To Note that, different rule tree can produce same validation rule, above rule can be rewritten as

rule := And(
				EqStr("Info.Type", "range"),
				Length("Info.Range", 2, 2),
				Array("Info.Range", Time("", "2006-01-02")),
				EqStr("Info.Type", "last"),
				InStr("Info.Granularity", "day", "week", "month"),

rule tree2

Although rule trees are different, fieldExpr of leaf nodes in trees are same, which can be used as cache, and the validation logic is same.


Rule is an interface, it has many implementations. Its implementations can be categorized into two kinds: composite rule and singleton rule.

Composite Rule

Composite Rule contains other rules.

Name Usage
Field(fieldExpr string, rule Rule) Rule Applies rule to validate fieldExpr
And(rules ...Rule) Rule It needs all rules pass
Or(rules ...Rule) Rule It needs any rule passed
Not(innerRule Rule) Rule opposite the rule
Array(fieldExpr string, innerRule Rule) Rule Applies rule to elements in array
Map(fieldExpr string, keyRule Rule, valueRule Rule) Rule Applies keyRule and valueRule to key and value in map

Singleton Rule

Singleton Rule can be categorized into comparison rule, enum rule and format rule.

Comparison Rule

Comparison Rule can be categorized into single field comparison rule and multi-field comparison rule

single field comparison rule includes:

EqInt(filedExpr string, equivalent int) Rule
NeInt(filedExpr string, inequivalent int) Rule
RangeInt(filedExpr string, ge int, le int) Rule

It also has the implementation of uint, stringfloattime.Time , Comparable.

multi-field comparison rule includes

CrossComparable(fieldExprLeft string, fieldExprRight string, op operand) Rule

fieldExprLeftfieldExprRight is to located the field involving comparsion, op is the operand.

CrossComparable supports int`uint\float\string\time.Time\Comparable`.

Enum Rule

Enum Rule includes

InStr(filedExpr string, enum ...string) Rule
InInt(filedExpr string, enum ...int) Rule
InUint(filedExpr string, enum ...uint) Rule
InFloat(filedExpr string, enum ...float64) Rule

Format Rule

Format Rule includes

Email(fieldExpr string) Rule
Number(fieldExpr string) Rule
URL(fieldExpr string) Rule
Ip(fieldExpr string) Rule


Customized Rule

In addition to above rules, user can pass validation function to Custome to achieve purpose of implementing customized rule, refer to example


Checekr is an interface

  • Add(rule Rule, prompt string). Add rule and error prompt of failing the rule.
  • Check(param interface{}) (bool, string, string). Validate a parameter. It returns if it passes the rule, error prompt and error message to tell which field doesn't pass which rule.

Error log And Customized Error Prompt

When defining rules, it can define the error prompt when rule failed.example

rule := checker.And(
		checker.Email("Email").Prompt("Wrong email format") // [1],
			checker.EqStr("Info.Type", "range"),
			checker.Length("Info.Range", 2, 2).Prompt("Range's length should be 2") // [2],
			checker.Array("Info.Range", checker.Time("", "2006-01-02")).
				Prompt("Range's element should be time format") // [3],

	validator := checker.NewChecker()
	validator.Add(rule, "wrong parameter") // [4]
    isValid, prompt, errMsg := validator.Check(item)

When rule fails, checker tries to return the rule's prompt([1]/[2]/[3] in code). If rule doesn't have its prompt, checker returns the prompt when adding the rule([4] in code).

errMsg is error log, is used to locate the filed that fails, refer it to example

Field Cache

From above graphic representation of rule tree, it can be found that when leaf node with same field expression, its value can be cached to reduce the cost of reflection.

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