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，终端输出位空，表示校验通过。