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HomeWeb Front-endJS Tutorialnode.js Sequelize implements single instance field or batch auto-increment and auto-decrement

一、单实例自增、自减

在Sequelize中,一个实例(Instance)表示数据库中的一行记录。Instance有两种:由Model.build()创建的非持久化实例,和由Model.create()等方法创建的持久化实例。无论是持久化还是非持久化实例,都会有increment() 、decrement()两人上方法,分别用于字段值的自增和自减两种操作。

instance.increment(fields, [options]) - 字段值自增

instance.decrement(fields, [options]) - 字段值自减

如,查找id为1的用户,并将其年龄自增1:

var User = sequelize.import('../lib/model/user/user');
User.findById(1).then(function(user){
 user.increment('age').then(function(user){
 console.log('success');
 })
})

   

其中increment()方法生成的SQL语句如下:

UPDATE `user` SET `age`=`age` + 1 WHERE `id` = 1

increment()和decrement()默认的自增、自减值是1。如果希望使用其它值,可在选项参数[options]中通过by参数指定。

如,将用户的number、age两个字段减小2,可以通过以下方式实现:

user.increment(['age', 'number'], {by:2}).then(function(user){
 console.log('success');
})

   

生成的SQL如下:

UPDATE `user` SET `age`=`age` + 2,`number`=`number` + 2 WHERE `id` = 1

   

fields参数还可以通过对象传入,并指定自增、自减值。这种情况下,会忽略options.by参数。

如,将用户的number增加2、age减小1:

user.increment({age:-1, number:2}, {by:5}).then(function(user){
 console.log('success');
})

   

生成的SQL如下:

UPDATE `user` SET `age`=`age` + -1,`number`=`number` + 2 WHERE `id` = 1

   

二、 批量自增、自减

increment()和decrement()都是针对单个实例进行自增或自减操作的,也就是说操作的数据为数据库中的一行数据。要实现类似如下批量自增、自减操作,就无法通过Instance操作:

UPDATE `user` SET `age`=`age` + 1 WHERE `number` > 10;

   

在Sequelize中,指量操作一般是通过模型(Model)来实现。但Model并没有increment()和decrement()方法,无法像Instance那样方便的进行自增或自减。

这时,我们可以通过Model.update()并借助sequelize中的顶级方法sequelize.literal()来实现:

sequelize.literal(val) - 创建字面量对象

sequelize.literal()方法用于创建一个字面量对象,该对象(val)会被直接传入所生成的SQL语句中,而不会进行任何转义。

如,将number大于10的用户年龄增加1:

User.update({sex:sequelize.literal('`age` +1')}, {where:{number:{$gt:10}}}).then(function(user){
 console.log('success');
})

   

生成的SQL语句如下:

UPDATE `user` SET `age`=`age` +1 WHERE `number` > 10

   

总结

以上就是这篇文章的全部内容了,希望本文的内容对大家的学习或者工作能带来一定的帮助,如果有疑问大家可以留言交流。

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