add model validation chapter

Home.md

@@ -22,6 +22,7 @@ This wiki is the main source of documentation for **developers** working with (o
 * [[Request Authentication]]
 * [[URL Query Parameters]]
 * [[Forms]]
+* [[Model Validation]]
 * [[File Server]]
 * [[View]]
 * [[Dependency Injection|dependency-injection]]

Model-validation.md

@@ -0,0 +1,125 @@
+Iris does not contain built-in method for validating request data such as "Models". However, you are not limited. In this example we will learn how to use the [**go-playground/validator.v9**](https://github.com/go-playground/validator) for request values validation.
+
+Check the full docs on tags usage [here](http://godoc.org/gopkg.in/go-playground/validator.v9#hdr-Baked_In_Validators_and_Tags).
+
+```sh
+$ go get gopkg.in/go-playground/validator.v9
+```
+
+Note that you need to set the corresponding binding tag on all fields you want to bind. For example, when binding from JSON, set `json:"fieldname"`.
+
+```go
+package main
+
+import (
+    "fmt"
+
+    "github.com/kataras/iris"
+
+    "gopkg.in/go-playground/validator.v9"
+)
+
+// User contains user information.
+type User struct {
+    FirstName      string     `json:"fname"`
+    LastName       string     `json:"lname"`
+    Age            uint8      `json:"age" validate:"gte=0,lte=130"`
+    Email          string     `json:"email" validate:"required,email"`
+    FavouriteColor string     `json:"favColor" validate:"hexcolor|rgb|rgba"`
+    Addresses      []*Address `json:"addresses" validate:"required,dive,required"`
+}
+
+// Address houses a users address information.
+type Address struct {
+    Street string `json:"street" validate:"required"`
+    City   string `json:"city" validate:"required"`
+    Planet string `json:"planet" validate:"required"`
+    Phone  string `json:"phone" validate:"required"`
+}
+
+// Use a single instance of Validate, it caches struct info.
+var validate *validator.Validate
+
+func main() {
+    validate = validator.New()
+
+    // Register validation for 'User'
+    // NOTE: only have to register a non-pointer type for 'User', validator
+    // internally dereferences during it's type checks.
+    validate.RegisterStructValidation(UserStructLevelValidation, User{})
+
+    app := iris.New()
+    app.Post("/user", func(ctx iris.Context) {
+        var user User
+        if err := ctx.ReadJSON(&user); err != nil {
+            // [handle error...]
+        }
+
+        // Returns InvalidValidationError for bad validation input,
+        // nil or ValidationErrors ( []FieldError )
+        err := validate.Struct(user)
+        if err != nil {
+
+            // This check is only needed when your code could produce
+            // an invalid value for validation such as interface with nil
+            // value most including myself do not usually have code like this.
+            if _, ok := err.(*validator.InvalidValidationError); ok {
+                ctx.StatusCode(iris.StatusInternalServerError)
+                ctx.WriteString(err.Error())
+                return
+            }
+
+            ctx.StatusCode(iris.StatusBadRequest)
+            for _, err := range err.(validator.ValidationErrors) {
+                fmt.Println()
+                fmt.Println(err.Namespace())
+                fmt.Println(err.Field())
+                fmt.Println(err.StructNamespace())
+                fmt.Println(err.StructField())
+                fmt.Println(err.Tag())
+                fmt.Println(err.ActualTag())
+                fmt.Println(err.Kind())
+                fmt.Println(err.Type())
+                fmt.Println(err.Value())
+                fmt.Println(err.Param())
+                fmt.Println()
+            }
+
+            return
+        }
+
+        // [save user to database...]
+    })
+
+    app.Run(iris.Addr(":8080"))
+}
+
+func UserStructLevelValidation(sl validator.StructLevel) {
+    user := sl.Current().Interface().(User)
+
+    if len(user.FirstName) == 0 && len(user.LastName) == 0 {
+        sl.ReportError(user.FirstName, "FirstName", "fname", "fnameorlname", "")
+        sl.ReportError(user.LastName, "LastName", "lname", "fnameorlname", "")
+    }
+}
+```
+
+Example request of JSON form:
+
+```json
+{
+    "fname": "",
+    "lname": "",
+    "age": 45,
+    "email": "mail@example.com",
+    "favColor": "#000",
+    "addresses": [{
+        "street": "Eavesdown Docks",
+        "planet": "Persphone",
+        "phone": "none",
+        "city": "Unknown"
+    }]
+}
+```
+
+Example can be found at: <https://github.com/kataras/iris/tree/master/_examples/http_request/read-json-struct-validation/main.go>.

_Sidebar.md

@@ -17,6 +17,7 @@
 * [[Request Authentication]]
 * [[URL Query Parameters]]
 * [[Forms]]
+* [[Model Validation]]
 * [[File Server]]
 * [[View]]
 * [[Dependency Injection|dependency-injection]]