Update README for Updating

README.md

@@ -47,9 +47,14 @@ go get -u github.com/jinzhu/gorm
       - [Query Chains](#query-chains)
       - [Preloading (Eager loading)](#preloading-eager-loading)
   - [Update](#update)
-      - [Update Without Callbacks](#update-without-callbacks)
+      - [Update All Fields](#update-all-fields)
+      - [Update Changed Fields](#update-changed-fields)
+      - [Update Selected Fields](#update-selected-fields)
+      - [Update Changed Fields Without Callbacks](#update-changed-fields-without-callbacks)
       - [Batch Updates](#batch-updates)
       - [Update with SQL Expression](#update-with-sql-expression)
+      - [Change Updating Values In Callbacks](#change-updating-values-in-callbacks)
+      - [Extra Update option](#extra-update-option)
   - [Delete](#delete)
       - [Batch Delete](#batch-delete)
       - [Soft Delete](#soft-delete)
@@ -453,66 +458,86 @@ db.Preload("Orders", "state = ?", "paid").Preload("Orders.OrderItems").Find(&use
 
 ## Update
 
+### Update All Fields
+
+`Save` will include all fields when perform the Updating SQL, even it is not changed
+
 ```go
-// Update an existing struct
 db.First(&user)
+
 user.Name = "jinzhu 2"
 user.Age = 100
 db.Save(&user)
-//// UPDATE users SET name='jinzhu 2', age=100, updated_at = '2013-11-17 21:34:10' WHERE id=111;
 
-db.Where("active = ?", true).Save(&user)
+//// UPDATE users SET name='jinzhu 2', age=100, birthday='2016-01-01', updated_at = '2013-11-17 21:34:10' WHERE id=111;
-//// UPDATE users SET name='jinzhu 2', age=100, updated_at = '2013-11-17 21:34:10' WHERE id=111 AND active = true;
+```
 
-// Update an attribute if it is changed
+### Update Changed Fields
+
+If you only want to update changed Fields, you could use `Update`, `Updates`
+
+```go
+// Update single attribute if it is changed
 db.Model(&user).Update("name", "hello")
-//// UPDATE users SET name='hello', updated_at = '2013-11-17 21:34:10' WHERE id=111;
+//// UPDATE users SET name='hello', updated_at='2013-11-17 21:34:10' WHERE id=111;
 
+// Update single attribute with combined conditions
 db.Model(&user).Where("active = ?", true).Update("name", "hello")
-//// UPDATE users SET name='hello', updated_at = '2013-11-17 21:34:10' WHERE id=111 AND active = true;
+//// UPDATE users SET name='hello', updated_at='2013-11-17 21:34:10' WHERE id=111 AND active=true;
 
-db.First(&user, 111).Update("name", "hello")
-//// SELECT * FROM users LIMIT 1;
-//// UPDATE users SET name='hello', updated_at = '2013-11-17 21:34:10' WHERE id=111;
 
-// Update multiple attributes if they are changed
+// Update multiple attributes with `map`, will only update those changed fields
 db.Model(&user).Updates(map[string]interface{}{"name": "hello", "age": 18, "actived": false})
+//// UPDATE users SET name='hello', age=18, actived=false, updated_at='2013-11-17 21:34:10' WHERE id=111;
 
-// Update multiple attributes if they are changed (update with struct only works with none zero values)
+// Update multiple attributes with `struct`, will only update those changed & non blank fields
 db.Model(&user).Updates(User{Name: "hello", Age: 18})
 //// UPDATE users SET name='hello', age=18, updated_at = '2013-11-17 21:34:10' WHERE id = 111;
 
-// Add extra SQL option for updating SQL
+// WARNING when update with struct, GORM will only update those fields that with non blank value
-db.Model(&user).Set("gorm:update_option", "OPTION (OPTIMIZE FOR UNKNOWN)").Update("name, "hello")
+// For below Update, nothing will be updated as "", 0, false are blank values of their types
-//// UPDATE users SET name='hello', updated_at = '2013-11-17 21:34:10' WHERE id=111 OPTION (OPTIMIZE FOR UNKNOWN);
+db.Model(&user).Updates(User{Name: "", Age: 0, Actived: false})
 ```
 
-### Update Without Callbacks
+### Update Selected Fields
 
-By default, update will call BeforeUpdate, AfterUpdate callbacks, if you want to update w/o callbacks and w/o saving associations:
+If you only want to update or ignore some fields when updating, you could use `Select`, `Omit`
 
 ```go
+db.Model(&user).Select("name").Updates(map[string]interface{}{"name": "hello", "age": 18, "actived": false})
+//// UPDATE users SET name='hello', updated_at='2013-11-17 21:34:10' WHERE id=111;
+
+db.Model(&user).Omit("name").Updates(map[string]interface{}{"name": "hello", "age": 18, "actived": false})
+//// UPDATE users SET age=18, actived=false, updated_at='2013-11-17 21:34:10' WHERE id=111;
+```
+
+### Update Changed Fields Without Callbacks
+
+Updating operations above will invoke `BeforeUpdate`, `AfterUpdate`, Update UpdatedAt timestamp, Save Associations callbacks, if you don't call them, you could use `UpdateColumn`, `UpdateColumns`
+
+```go
+// Update single attribute, similar with `Update`
 db.Model(&user).UpdateColumn("name", "hello")
 //// UPDATE users SET name='hello' WHERE id = 111;
 
-// Update with struct only works with none zero values, or use map[string]interface{}
+// Update multiple attributes, similar with `Updates`
 db.Model(&user).UpdateColumns(User{Name: "hello", Age: 18})
 //// UPDATE users SET name='hello', age=18 WHERE id = 111;
 ```
 
 ### Batch Updates
 
+Callbacks won't run when do batch updates
+
 ```go
-db.Table("users").Where("id = ?", 10).Updates(map[string]interface{}{"name": "hello", "age": 18})
+db.Table("users").Where("id IN (?)", []int{10, 11}).Updates(map[string]interface{}{"name": "hello", "age": 18})
-//// UPDATE users SET name='hello', age=18 WHERE id = 10;
+//// UPDATE users SET name='hello', age=18 WHERE id IN (10, 11);
 
 // Update with struct only works with none zero values, or use map[string]interface{}
 db.Model(User{}).Updates(User{Name: "hello", Age: 18})
 //// UPDATE users SET name='hello', age=18;
 
-// Callbacks won't run when do batch updates
+// Get updated records count with `RowsAffected`
-
-// Use `RowsAffected` to get the count of affected records
 db.Model(User{}).Updates(User{Name: "hello", Age: 18}).RowsAffected
 ```
 
@@ -520,10 +545,10 @@ db.Model(User{}).Updates(User{Name: "hello", Age: 18}).RowsAffected
 
 ```go
 DB.Model(&product).Update("price", gorm.Expr("price * ? + ?", 2, 100))
-//// UPDATE "products" SET "code" = 'L1212', "price" = price * '2' + '100', "updated_at" = '2013-11-17 21:34:10' WHERE "id" = '2';
+//// UPDATE "products" SET "price" = price * '2' + '100', "updated_at" = '2013-11-17 21:34:10' WHERE "id" = '2';
 
 DB.Model(&product).Updates(map[string]interface{}{"price": gorm.Expr("price * ? + ?", 2, 100)})
-//// UPDATE "products" SET "code" = 'L1212', "price" = price * '2' + '100', "updated_at" = '2013-11-17 21:34:10' WHERE "id" = '2';
+//// UPDATE "products" SET "price" = price * '2' + '100', "updated_at" = '2013-11-17 21:34:10' WHERE "id" = '2';
 
 DB.Model(&product).UpdateColumn("quantity", gorm.Expr("quantity - ?", 1))
 //// UPDATE "products" SET "quantity" = quantity - 1 WHERE "id" = '2';
@@ -532,6 +557,26 @@ DB.Model(&product).Where("quantity > 1").UpdateColumn("quantity", gorm.Expr("qua
 //// UPDATE "products" SET "quantity" = quantity - 1 WHERE "id" = '2' AND quantity > 1;
 ```
 
+### Change Updating Values In Callbacks
+
+If you want to change updating values in callbacks using `BeforeUpdate`, `BeforeSave`, you could use `scope.SetColumn`, for example:
+
+```go
+func (user *User) BeforeSave(scope *gorm.Scope) (err error) {
+  if pw, err := bcrypt.GenerateFromPassword(user.Password, 0); err == nil {
+    scope.SetColumn("EncryptedPassword", pw)
+  }
+}
+```
+
+### Extra Update option
+
+```go
+// Add extra SQL option for updating SQL
+db.Model(&user).Set("gorm:update_option", "OPTION (OPTIMIZE FOR UNKNOWN)").Update("name, "hello")
+//// UPDATE users SET name='hello', updated_at = '2013-11-17 21:34:10' WHERE id=111 OPTION (OPTIMIZE FOR UNKNOWN);
+```
+
 ## Delete
 
 ```go