View source for Mongo DB - Related Models

[[Category:Node.js]]
[[Category:MongoDb]]

== Using References (Normalization) ==
Consistency
 let author = { 
    name:'Ali'
 }

 let course = {
    author:'id' 
 }
=== How it's defined in model ===
 const Course = mongoose.model('Course', new mongoose.Schema({
    name:string
    author:{
       type:mongoose.Schema.Types.ObjectId,
       ref:'Author'
    } 
 }));
=== Querying data (Population) ===
 async function listCourses(){
    const courses = await Course
       .find()
       .populate('author')
       .select('name author');
    console.log(courses);
  }

in order to include only some of the fields of populated data
       .populate('author', 'name')
in order to exclude some of the fields of populated data
       .populate('author', 'name -_id')

== Using Embedded Documents (Denormalization) ==
Performance
 let course = {
    author:{
      name:'Ali'
    } 
 }
[https://www.udemy.com/nodejs-master-class/learn/v4/t/lecture/9993130?start=0 https://www.udemy.com/nodejs-master-class/learn/v4/t/lecture/9993130?start=0]
=== How it's defined in model ===
By giving the schema name :
 const Course = mongoose.model('Course', new mongoose.Schema({
    name:string
    author: authorSchema
 }));
=== Creating ===
 async function createCourse(name, author){
   const course = new Course({
     name,
     author
 });
 
 createCourse('Node Course', new Author({ name:'Ali'}));
it saves as subdocuments and only updated by parent doc. 

=== Update directly in DB ===
 async function updateAuthor(courseId){
   const course = await Course.update({ _id: courseId }, {
      $set: {
        'author.name:'John Smith'
      }
    });
  }
 
 updateAuthor('123123123');
== Hybrid ==
it's good for snapshot of data in a given point of time
 let author = {
    name : 'Ali'
    // other properties 
 }

 let course = {
    author: {
      id:'ref',
      name:'Ali'
     }
 }
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See Also : [[Mongo DB usage in Node]]