本文实例讲述了MongoDB多表关联查询操作。分享给大家供大家参考，具体如下：

Mongoose的多表关联查询

首先，我们回忆一下，MySQL多表关联查询的语句：

student表：

calss表：

通过student的classId关联进行查询学生名称，班级的数据：

SELECT student.name,student.age,class.name FROM student,class WHERE student.classId = class.id

Mongoose多表联合查询(还是以众所周知的学生、班级作为实例)

· 表结构的定义(schemas目录下)

1. student表(student.js)

var mongoose = require('mongoose');var Schema = mongoose.Schema;var StudentSchema = new mongoose.Schema({ name: String, calssId: { type: Schema.Types.objectId, ref: 'class' }, age: Number, number: Number, meta: { createAt: { type: Date, default: Date.now() }, updateAt: { type: Date, default: Date.now() } } });module.exports = StudentSchema;

2. class表(class.js)

var mongoose = require('mongoose');var Schema = mongoose.Schema;var ClassSchema = new mongoose.Schema({ name: String, meta: { createAt: { type: Date, default: Date.now() }, updateAt: { type: Date, default: Date.now() } } });module.exports = ClassSchema;

· 生成Model（model目录下）

1. student Model（student.js）

var mongoose = require('mongoose');var StudentSchema = require('../schemas/student');var Student = mongoose.model('student', StudentSchema);module.exports = Student;

2. class Model（class.js）

var mongoose = require('mongoose');var ClassSchema = require('../schemas/class');var Class = mongoose.model('class', ClassSchema);module.exports = Class;

· Model进行数据的查询操作

1. 将静态类的方法加到Model的编译中

StudentSchema.static = { fetch: function(cb){ return this .find({}) .sort('meta.updateAt') //按更新的时间排序 }}

2. 将静态类方法加到Model中

StudentSchema.static('fetch', function(cb){ return this .find({}, cb) .sort('meta.updateAt')})

3. 直接调用model的find()方法

查询的结果均为：

[
{
_id: '5a05222f583e5720b8660191',
name: '张三',
age: 18,
number: 11,
classId: '5a0036512b740f32e4371e66'
},
{
_id: '5a05222f583e5720b8660091',
name: '李四',
age: 19,
number: 11,
classId: '5a0036512b740f32e1371e66'
},
{
_id: '5a05222f583e5720b18660191',
name: '赵五',
age: 17,
number: 11,
classId: '5a0036512b7420f32e4371e66'
}
]

· 多表联合查询（学生对应班级）

StudentSchema.static = { findStudentWithClass: function (cb) { return this .find({}) .populate('classId')//注意这是联合查询的关键 .sort('meta.updateAt') .exec(cb) }}

查询结果：

[
{
_id: '5a05222f583e5720b8660191',
name: '张三',
age: 18,
number: 11,
classId: {
_id: '5a0036512b740f32e4371e66',
name: '一年1班'
}
},
{
_id: '5a05222f583e5720b8660091',
name: '李四',
age: 18,
number: 11,
classId: {
_id: '5a0036512b740f32e1371e66',
name: '二年2班'
}
},
{
_id: '5a05222f583e5720b18660191',
name: '赵五',
age: 18,
number: 11,
classId: {
_id: '5a0036512b7420f32e4371e66',
name: '一年2班'
}
}
]

· 由上面的实例可知，mongoose的多表联合查询的关键：

1. 数据模式结构定义需要利用关键字ref定义关联

var Schema = new mongoose.Schema({ field: { type: mongoose.Schema.Type.ObjectId, ref: 'model' }});Schema.static = { fetch: function(cb){ return this .find({}) .populate('field') .exec(cb) } }var Model = mongoose.Model('model',Schema );

希望本文所述对大家MongoDB数据库程序设计有所帮助。