校验组件支持强大的递归校验（嵌套校验）特性。如果给定的校验数据中的属性或者键值为struct/map/slice类型时，将会被自动执行递归校验。我们来看几个示例：
示例1，递归校验：struct
package main
import (
"fmt"
"github.com/gogf/gf/v2/frame/g"
"github.com/gogf/gf/v2/os/gctx"
)
type SearchReq struct {
Key string `v:"required"`
Option SearchOption
}
type SearchOption struct {
Page int `v:"min:1"`
Size int `v:"max:100"`
}
func main() {
var (
ctx = gctx.New()
req = SearchReq{
Key: "GoFrame",
Option: SearchOption{
Page: 1,
Size: 10000,
},
}
)
err := g.Validator().Data(req).Run(ctx)
fmt.Println(err)
}执行后，终端输出：
The Size value `10000` must be equal or lesser than 100示例2，递归校验：slice
package main
import (
"fmt"
"github.com/gogf/gf/v2/frame/g"
"github.com/gogf/gf/v2/os/gctx"
)
func main() {
type Student struct {
Name string `v:"required#Student Name is required"`
Age int
}
type Teacher struct {
Name string
Students []Student
}
var (
ctx = gctx.New()
teacher = Teacher{}
data = g.Map{
"name": "john",
"students": `[{"age":2},{"name":"jack", "age":4}]`,
}
)
err := g.Validator().Assoc(data).Data(teacher).Run(ctx)
fmt.Println(err)
}执行后，终端输出：
Student Name is required示例3，递归校验：map
package main
import (
"fmt"
"github.com/gogf/gf/v2/frame/g"
"github.com/gogf/gf/v2/os/gctx"
)
func main() {
type Student struct {
Name string `v:"required#Student Name is required"`
Age int
}
type Teacher struct {
Name string
Students map[string]Student
}
var (
ctx = gctx.New()
teacher = Teacher{
Name: "Smith",
Students: map[string]Student{
"john": {Name: "", Age: 18},
},
}
)
err := g.Validator().Data(teacher).Run(ctx)
fmt.Println(err)
}执行后，终端输出：
Student Name is required注意事项：空对象对递归校验的影响
package main
import (
"fmt"
"github.com/gogf/gf/v2/frame/g"
"github.com/gogf/gf/v2/os/gctx"
)
func main() {
type Student struct {
Name string `v:"required"`
}
type Teacher struct {
Students Student
}
var (
ctx = gctx.New()
teacher = Teacher{}
data = g.Map{
"students": nil,
}
)
err := g.Validator().Assoc(data).Data(teacher).Run(ctx)
fmt.Println(err)
}执行后，终端输出：
Student Name is required有同学可能会觉得奇怪，明明我都没有传递Student字段值，为什么还会递归校验Student结构体里面的Name字段？这是因为这里的Student属性是个空结构体，是带有默认值的（Name默认值为空字符串）。递归校验里面，虽然Student不是必须参数，这个意思是你可以不传递，但是只要传递了就会按照里面属性的校验规则执行校验（带有默认值的空对象也算是有值）。可以对比和以下代码的差别：
package main
import (
"fmt"
"github.com/gogf/gf/v2/frame/g"
"github.com/gogf/gf/v2/os/gctx"
)
func main() {
type Student struct {
Name string `v:"required"`
}
type Teacher struct {
Students *Student
}
var (
ctx = gctx.New()
teacher = Teacher{}
data = g.Map{
"students": nil,
}
)
err := g.Validator().Assoc(data).Data(teacher).Run(ctx)
fmt.Println(err)
}和前一示例的唯一差异在于Student属性从结构体改为了结构体指针*Student，这样该属性不是空对象便没有默认值了。执行后，终端输出为空，表示校验通过。