golang mongodb 多表查询 mongodb多表联合查询

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;
/*定义数据模式*/
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()
        }
    }
    /*更新时间的*/
});
module.exports = StudentSchema;

2. class表(class.js)

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
/*定义数据模式*/
var ClassSchema = new mongoose.Schema({
    name: String,
    meta: {
        createAt: {
            type: Date,
            default: Date.now()
        },
        updateAt: {
            type: Date,
            default: Date.now()
        }
    }
    /*更新时间的*/
});
module.exports = ClassSchema;

· 生成Model（model目录下）

1. student Model（student.js）

var mongoose = require('mongoose');
var StudentSchema = require('../schemas/student');

/*通过model编译模式为模型*/
var Student = mongoose.model('student', StudentSchema);

/*导出Student模型 模块*/
module.exports = Student;

2. class Model（class.js）

var mongoose = require('mongoose');
var ClassSchema = require('../schemas/class');

/*通过model编译模式为模型*/
var Class = mongoose.model('class', ClassSchema);

/*导出Class模型 模块*/
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'
        }
    }
]

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 );