Update validations README

README.md

@@ -1,10 +1,88 @@
 # Validations
 
-Validations provides a means to validate [GORM-backend](https://github.com/jinzhu/gorm) models when creating and updating them.
+Validations provides a means to [*validate*](https://en.wikipedia.org/wiki/Data_validation) [GORM](https://github.com/jinzhu/gorm) models when creating and updating them.
 
-## Documentation
+### Register GORM Callbacks
 
-<https://doc.getqor.com/plugins/validation.html>
+Validations uses [GORM](https://github.com/jinzhu/gorm) callbacks to handle *validations*, so you will need to register callbacks first:
+
+```go
+import (
+  "github.com/jinzhu/gorm"
+  "github.com/qor/validations"
+)
+
+func main() {
+  db, err := gorm.Open("sqlite3", "demo_db")
+
+  validations.RegisterCallbacks(db)
+}
+```
+
+### Usage
+
+After callbacks have been registered, attempting to create or update any record will trigger the `Validate` method that you have implemented for your model. If your implementation adds or returns an error, the attempt will be aborted.
+
+```go
+type User struct {
+  gorm.Model
+  Age uint
+}
+
+func (user User) Validate(db *gorm.DB) {
+  if user.Age <= 18 {
+    db.AddError(errors.New("age need to be 18+"))
+  }
+}
+
+db.Create(&User{Age: 10})         // won't insert the record into database, as the `Validate` method will return error
+
+var user User{Age: 20}
+db.Create(&user)                  // user with age 20 will be inserted into database
+db.Model(&user).Update("age", 10) // user's age won't be updated, will return error `age need to be 18+`
+
+// If you have added more than one error, could get all of them with `db.GetErrors()`
+func (user User) Validate(db *gorm.DB) {
+  if user.Age <= 18 {
+    db.AddError(errors.New("age need to be 18+"))
+  }
+  if user.Name == "" {
+    db.AddError(errors.New("name can't be blank"))
+  }
+}
+
+db.Create(&User{}).GetErrors() // => []error{"age need to be 18+", "name can't be blank"}
+```
+
+## [Govalidator](https://github.com/asaskevich/govalidator) integration
+
+Qor [Validations](https://github.com/qor/validations) supports [govalidator](https://github.com/asaskevich/govalidator), so you could add a tag into your struct for some common *validations*, such as *check required*, *numeric*, *length*, etc.
+
+```
+type User struct {
+  gorm.Model
+  Name           string `valid:"required"`
+  Password       string `valid:"length(6|20)"`
+  SecurePassword string `valid:"numeric"`
+  Email          string `valid:"email"`
+}
+```
+
+## Customize errors on form field
+
+If you want to display errors for each form field in [QOR Admin](http://github.com/qor/admin), you could register your error like this:
+
+```go
+func (user User) Validate(db *gorm.DB) {
+  if user.Age <= 18 {
+    db.AddError(validations.NewError(user, "Age", "age need to be 18+"))
+  }
+}
+```
+
+## Try it out for yourself
+
+Checkout the [http://demo.getqor.com/admin/products/1](http://demo.getqor.com/admin/products/1) demo, change `Name` to be a blank string and save to see what happens.
 
 ## License