Detailed explanation of MongoDB Multi-table Association query Operation example
This paper gives an example of MongoDB multi-table association query operation. Share with you for your reference, the details are as follows:
Multi-table Association query of Mongoose
First, let's recall that the statement of the MySQL multi-table associative query:
Student table:
Calss table:
Query the student name and class data through the classId association of student:
SELECT student.name,student.age,class.name FROM student,class WHERE student.classId = class.id
Mongoose multi-table federated query (or taking well-known students and classes as examples)
Definition of table structure (under schemas directory)
1. Student table (student.js)
Var mongoose = require ('mongoose'); var Schema = mongoose.Schema / * define data 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 ()}} / * update time * /}) Module.exports = StudentSchema
2. Class table (class.js)
Var mongoose = require ('mongoose'); var Schema = mongoose.Schema;/* define data schema * / var ClassSchema = new mongoose.Schema ({name: String, meta: {createAt: {type: Date, default: Date.now ()}, updateAt: {type: Date, default: Date.now ()}} / * update time * /}); module.exports = ClassSchema
Generate Model (under the model directory)
1. Student Model (student.js)
Var mongoose = require ('mongoose'); var StudentSchema = require ('.. / schemas/student'); / * compile model through model to model * / var Student = mongoose.model ('student', StudentSchema); / * Export Student model module * / module.exports = Student
2. Class Model (class.js)
Var mongoose = require ('mongoose'); var ClassSchema = require ('.. / schemas/class'); / * compile model through model to model * / var Class = mongoose.model ('class', ClassSchema); / * Export Class model module * / module.exports = Class
Model carries on the data query operation
1. Add methods of static classes to the compilation of Model
StudentSchema.static = {fetch: function (cb) {return this. Find ({}) .sort ('meta.updateAt') / / sort by updated time}}
two。 Add static class methods to Model
StudentSchema.static ('fetch', function (cb) {return this. Find ({}, cb). Sort (' meta.updateAt')})
3. Directly call the find () method of model
The results of the query are:
[
{
_ id: '5a05222f583e5720b8660191'
Name: 'Zhang San'
Age: 18
Number: 11
ClassId: '5a0036512b740f32e4371e66'
}
{
_ id: '5a05222f583e5720b8660091'
Name:'Li Si'
Age: 19
Number: 11
ClassId: '5a0036512b740f32e1371e66'
}
{
_ id: '5a05222f583e5720b18660191'
Name: 'Zhao Wu'
Age: 17
Number: 11
ClassId: '5a0036512b7420f32e4371e66'
}
]
Multi-table joint query (student corresponding class)
StudentSchema.static = {findStudentWithClass: function (cb) {return this. Find ({}) .populate ('classId') / / Note this is the key to federated queries. Sort (' meta.updateAt') .exec (cb)}}
Query results:
[
{
_ id: '5a05222f583e5720b8660191'
Name: 'Zhang San'
Age: 18
Number: 11
ClassId: {
_ id: '5a0036512b740f32e4371e66'
Name: "one class a year"
}
}
{
_ id: '5a05222f583e5720b8660091'
Name:'Li Si'
Age: 18
Number: 11
ClassId: {
_ id: '5a0036512b740f32e1371e66'
Name: "Class 2, year 2"
}
}
{
_ id: '5a05222f583e5720b18660191'
Name: 'Zhao Wu'
Age: 18
Number: 11
ClassId: {
_ id: '5a0036512b7420f32e4371e66'
Name:'2 classes a year'
}
}
]
As can be seen from the above example, the key to mongoose's multi-table federated query:
1. Data schema structure definition requires the use of the keyword ref to define associations
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)
It is hoped that what is described in this article will be helpful to the programming of MongoDB database.
