Update callback document

documents/callbacks.md

@@ -2,51 +2,66 @@
 
 <!-- toc -->
 
-Callbacks are methods defined on the pointer of struct.
-If any callback returns an error, gorm will stop future operations and rollback all changes.
-
-Here is the list of all available callbacks:
-(listed in the same order in which they will get called during the respective operations)
+You could define callback methods to pointer of model struct, it will be called when creating, updating, querying, deleting, if any callback returns an error, gorm will stop future operations and rollback all changes.
 
 ### Creating An Object
 
+Available Callbacks for creating
+
 ```go
+// begin transaction
 BeforeSave
 BeforeCreate
 // save before associations
+// update timestamp `CreatedAt`, `UpdatedAt`
 // save self
+// reload fields that have default value and its value is blank
 // save after associations
 AfterCreate
 AfterSave
+// commit or rollback transaction
 ```
+
 ### Updating An Object
 
+Available Callbacks for updating
+
 ```go
+// begin transaction
 BeforeSave
 BeforeUpdate
 // save before associations
+// update timestamp `UpdatedAt`
 // save self
 // save after associations
 AfterUpdate
 AfterSave
+// commit or rollback transaction
 ```
 
-### Destroying An Object
+### Deleting An Object
+
+Available Callbacks for deleting
 
 ```go
+// begin transaction
 BeforeDelete
 // delete self
 AfterDelete
+// commit or rollback transaction
 ```
 
-### After Find
+### Querying An Object
+
+Available Callbacks for querying
 
 ```go
 // load data from database
+// Preloading (edger loading)
 AfterFind
 ```
 
-### Example
+### Callback Examples
 
 ```go
 func (u *User) BeforeUpdate() (err error) {
@@ -65,10 +80,8 @@ func (u *User) AfterCreate() (err error) {
 }
 ```
 
-Save/delete operations in gorm are running in a transaction.
-Changes made in that transaction are not visible unless it is commited.
-So if you want to use those changes in your callbacks, you need to run your SQL in the same transaction.
-For this Gorm supports passing transactions to callbacks like this:
+Save/Delete operations in gorm are running in transactions, so changes made in that transaction are not visible unless it is commited.
+If you want to use those changes in your callbacks, you need to run your SQL in the same transaction. So you need to pass current transaction to callbacks like this:
 
 ```go
 func (u *User) AfterCreate(tx *gorm.DB) (err error) {
@@ -76,3 +89,10 @@ func (u *User) AfterCreate(tx *gorm.DB) (err error) {
 	return
 }
 ```
+
+```go
+func (u *User) AfterCreate(scope *gorm.Scope) (err error) {
+  scope.DB().Model(u).Update("role", "admin")
+	return
+}
+```