I want to create a schema where I can add the same item type as a child to itself.
For instance, a page can be a sub-page with the same properties.
You can use mongoose.Schema.ObjectId and make a reference to the same schema.
In your case, it might be like this:
const mongoose = require('mongoose')
const PageSchema = new mongoose.Schema({
name: {
type: String
},
subPage: {
type: mongoose.Schema.ObjectId,
ref: 'Page'
}
})
module.exports = mongoose.model('Page', PageSchema)
By the way, don't forget to register your schema with the same name as you use in the reference. In the above example, it is registered as Page.
Related
What is the difference between nesting schema in schema (subdocuments) vs creating two separate models and referring to them, What about their performance?
subdocuments:
const postSchema = new Schema({
title: String,
content: String
});
const userSchema = new Schema({
name: String,
posts: [postSchema]
});
module.export = mongoose.model('User', userSchema);
nested models (Populating by reference):
const postSchema = new Schema({
title: String,
content: String,
author: { type: String, ref: 'User' }
});
module.export = mongoose.model('Post', postSchema);
const userSchema = new Schema({
name: String,
posts: [{ type: Schema.Types.ObjectId, ref: 'Post'}]
});
module.export = mongoose.model('User', userSchema);
Edit: This is not a duplicate question.
In this question: Mongoose subdocuments vs nested schema - mongoose subdocuments and nested schema is exactly the same.
BUT nested models creating a separate collection in database.
My question is what is diffrence in nested schema vs nested models, not subdocuments vs nested schema.
When using subdocuments, you actually have a copy of the data within your parent-document, wich allows you to get all the document + sub-document-data in a single query.
When using "nested models" you're not really nesting them, but referencing from the parent-model to the child-model. In this case you have to use population, which means you can't get all the data in a single query.
In short: subdocuments actually nest the data, and your "nested models" only reference them via their id
This question is similar to: this question
Working with Mongoose, I have something like the following code. (I've prefixed the files with numbers, so I can load them in the order they appear in the 'models' directory, but still control the loading order.)
In 100-employee.server.model.js:
var mongoose = require('mongoose'),
Schema = mongoose.Schema;
var EmployeeSchema = new Schema({
name: {
type: String,
default: ''
},
company: {
type: Schema.ObjectId,
ref: 'Company'
},
subordinates: [EmployeeSchema],
});
mongoose.model('Employee', EmplyeeSchema);
Then, in 200-company-server.js, I have:
var mongoose = require('mongoose'),
Schema = mongoose.Schema;
var CompanySchema = new Schema({
name: {
type: String,
default: ''
},
CEO: {
type: Schema.ObjectId,
ref: 'Employee'
}
});
mongoose.model('Company', CompanySchema);
Obviously, this doesn't work, since Company is referenced before it is registered. And, loading these in the opposite order doesn't work for the same reason. What I need, is a logical data structure like:
{
name: 'Acme, Inc',
CEO: {
name: 'Karen',
subordinates: [{
name: 'Bob',
subordinates: [{
name: 'Lisa',
subordinates: []
},
name: 'Jerry',
subordinates: []
}]
}]
}
}
(I think I got all of my brackets in place. I just typed that JSON to illustrate the need.)
I could just use an ObjectId for 'company' in EmployeeSchema, but it doesn't fix the problem. I still get a complaint that Company hasn't been registered.
Someone will ask for the use case, so here it is:
I have a bunch of companies.I have a hierarchy of employees of a company. And, I've got a bunch of companies. For each company, I need to know the CEO, without having to search all of my employees for the one with no parent, that has an ObjectId ref Company, but that still runs into the same problem.
Any suggestions?
OK, I've come up with an answer, or at least a workaround. Doesn't feel very elegant. In fact I actively dislike it, but it works. Would love to see a better solution. In 100-company-server.js, define the parent entity first, like so:
var mongoose = require('mongoose'),
Schema = mongoose.Schema;
var CompanySchema = new Schema({
name: {
type: String,
default: ''
},
CEO: {
name: { // This is the company name, so probably a bad example
type: String,
default: ''
}, {
shoeSize: Number
}, etc ...
}
});
mongoose.model('Company', CompanySchema);
The key thing to notice here is that instead of making CEO an ObjectId ref 'Employee' I supplied an object that uses the same properties as my Employee schema. Depending on how you want to use it, you may have to coerce that into an Employee object in the controller. Or, there might be a clever way to use a virtual to do the same thing (http://mongoosejs.com/docs/guide.html) But, the virtual would just have to be defined AFTER the EmployeeSchema and model.
In 200-employee.server.js, something like the following:
var mongoose = require('mongoose'),
Schema = mongoose.Schema,
CompanySchema = mongoose.model('Company').schema; // so you can use this
// after your Employee
// is defined
var EmployeeSchema = new Schema({
name: {
type: String,
default: ''
},
company: {
type: Schema.ObjectId,
ref: 'Company'
},
subordinates: [], // Just an empty array. You fill it with Employees in the controller. You could use a virtual to do the same thing, probably.
});
mongoose.model('Employee', EmployeeSchema);
So, it's kind of ugly, but it works.
Key points:
In defining CompanySchema, you don't use an ObjectId ref 'Employee'.
Instead, you define an object that looks like a Company object.
Since this object doesn't have an _id, you have to work around that in the
controller. In my case, this works fine. But, for many/most use cases, this
probably would not. You'd have to work around this with clever virtuals
and/or the controller.
Use a simple array, without type, to store your children (suborinates in
this example.
The array works just fine, and returns objects just as if you used an array
of ObjectId ref Employee.
Making the Company refer to an Employee (which hasn't been defined yet), you
have to convert a generic object into an Employee object. But, there are
many ways to do that.
There is, undoubtedly, a better way to do this.
I have this 2 schemas in mongoose:
The Booking schema
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var bookingSchema = new Schema({
bookingNO: { type: Number, unique: true},
plateNO: String,
startDate: String,
bookedTime: Number,
creator: {type: Schema.Types.ObjectId, ref: 'User'}
});
var Booking = mongoose.model('Booking', bookingSchema);
The User schema:
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var userSchema = new Schema({
username: String,
password: String,
balance: Number,
bookings: [{type: Schema.Types.ObjectId, ref: 'Booking'}]
});
var User = mongoose.model('User', userSchema);
The problem with this design is:
Some Bookings were NOT created by a user - in which case the 'creator' field in Booking would be empty. Likewise, some Users do NOT necessarily contain a Booking - they may later on.
I was thinking about deleting the creator and bookings fields from the 2 Schemas, and using the { strict: false } option in Mongoose. Would this be the best option ?
If this is the case, I would have to add the 'creator' property to the Booking model, and 'bookings' property to the User, which would then get saved to the DB.
MOST importantly, due to the fact that I've removed the references from the Schema, how do I go about creating the reference in the case of using { strict: false } ?
Thanks in advance.
Unless a field has require:true flag, it can be left empty.
If you have a field which isn't defined in the Mongoose schema but is present in a document in MongoDB, you'll have to use doc.get('field') instead of just doc.field. Similarly for saving doc.set('field', value) and strict:false will be required otherwise it won't persist.
IMO you should have your schema inclusive rather than exclusive. Mongoose is just a wrapper for your data in MongoDB which at its heart is already schemaless.
In your specific case, you can create a booking without specifying a 'creator', because its of type ObjectId Mongoose will simply create the document and will leave that field empty. The user.bookings is a different matter as it is an Array, in which case Mongoose will always default to an empty array, even if it was left undefined when creating the document. In this case, would it be that bad to just leave the empty array there? It still represents the data accurately, where the user simply has no bookings, but are still able to potentially have them. If you explicitly don't want bookings, then yes, you'll either have to deal with strict: false, or manually $unset/delete the field from the documents.
My mongo record is like this:
{
"_id":{"$oid":"5550b6de437f572112a29f1a"},
"cv_count":177732,
"gender_info": {"male_count": 50, "female_count": 32}
"stability_info_list":[{"ratio":8.802558610369414e-05,"total_count":34081,"years":0},{"ratio":5.868372406912943e-05,"total_count":34081,"years":1}],
"zhineng_id":"IT Manager"
}
I write the schema like this:
var ZhinengGenderSchema = new Schema({
male_count: Number,
female_count: Number
});
var ZhinengStabilitySchema = new Schema({
ratio: Number,
total_count: Number,
years: Number
});
var ZhinengStats = new Schema({
cv_count: Number,
gender_info: ZhinengGenderSchema,
stability_info_list: [ZhinengStabilitySchema],
zhineng_id: String
})
But I got this excetion:
TypeError: Undefined type `undefined` at `gender_info`
Did you try nesting Schemas? You can only nest using refs or arrays.
so mongoose doesn't support nest schemas? But my database has already been there, I cannot change, so how can I define my schema?
Just don't create a new schema for the subdocuments and you should be fine, i.e.:
var ZhinengGenderSchema = {
male_count: Number,
female_count: Number
};
var ZhinengStabilitySchema = {
ratio: Number,
total_count: Number
years: Number
};
var ZhinengStats = new Schema({
cv_count: Number,
gender_info: ZhinengGenderSchema,
stability_info_list: [ZhinengStabilitySchema],
zhineng_id: String
})
With mongoose you can define nesting (embedded) schemas in Array, like this:
var mongoose = require('mongoose'),
Schema = mongoose.Schema;
var bookSchema = new Schema({
value: { type: String }
});
var authorSchema = new Schema({
books: [bookSchema]
});
Or by reference
var mongoose = require('mongoose'),
Schema = mongoose.Schema,
ObjectId = mongoose.Schema.Types.ObjectId;
var auhtorSchema = new Schema({
book: { type: ObjectId, ref: 'Book'}
});
You may choose what is more appropriate for you
As far as I know, this is due to a current limitation of Mongoose. You cannot
declare a schema field to include a single sub-document: you have to use an array, instead. See this: https://github.com/Automattic/mongoose/pull/585
You can set up later the proper business logic in order to ensure that only one sub-element will be added.
Try this:
var ZhinengStats = new Schema({
cv_count: Number,
gender_info: [ZhinengGenderSchema],
stability_info_list: [ZhinengStabilitySchema],
zhineng_id: String
})
This way, each sub-document has got its own _id in MongoDB (even though it does not lie in a specific collection). See more: http://mongoosejs.com/docs/subdocs.html
You could also prefer something like this:
var ZhinengStats = new Schema({
cv_count: Number,
gender_info: [{male_count: Number, female_count: Number}],
stability_info_list: [ZhinengStabilitySchema],
zhineng_id: String
})
In this case, you nest a schema inside another. The single gender_info element does not have the dignity of a document.
I have a question about nesting Mongoose schema.
Here is a simple code snippet
var aSchema = new Schema({bar: String});
var bSchema = new Schema({a: aSchema, foo: String});
var cSchema = new Schema({as: [aSchema], foo:String});
This will throw TypeError on bSchema: TypeError: Undefined type at 's' Did you try nesting Schemas? You can only nest using refs or arrays., but works fine for cSchema.
Just want to ask why bSchema does not work. Cannot find explanation in Mongoose doc. Thanks.
MongoDB is not a relational database. This can cause confusion for some who are used to the RDBS model (I still get tripped up occasionally...but I'm really not a DB guy).
Oftentimes, you'll find it beneficial to reference other documents in your Mongo entities. Mongoose schemas provide a very simple and effective way to do this that feels very relational.
When defining a schema that will store a reference to a different type of document, you define the relevant property as an object with a type and a ref. Typically when defining schema properties, you can simply say: a: Number; however, Mongoose provides many different options for a schema property other than type:
a: {
type: Number,
required: true
}
Setting required: true will prevent us from saving a document where the a property is not present.
Once you understand how to define your schemas with object definitions, you can leverage Mongoose's population mechanic:
a: {
type: Mongoose.Schema.ObjectId,
ref: 'a'
}
This tells Mongoose to store the ObjectId (a Mongoose-specific identifier) of a specific a document as the a property of our schema. Still following me?
When setting this property on a Mongoose document, you can simply say: doc.a = myA. When you go to save doc, Mongoose will automagically make the conversion and only store the ID in your database.
When retrieving a document that references another schema, you'll need to populate. I won't go into that, but its pretty simple - check out the documentation.
I was facing this issue as I was completely new to the MongoDB. Later I found we need to use the relationship as below with the help of Mongoose.
Below is my country schema.
var mongoose = require("mongoose");
var Schema = mongoose.Schema;
var ObjectId = Schema.Types.ObjectId;
var CountrySchema = new Schema({
name: { type: String, required: true },
activeStatus: Boolean,
createdOn: Date,
updatedOn: Date
});
And I can use this schema in my State schema as follows.
var mongoose = require("mongoose");
var Schema = mongoose.Schema;
var ObjectId = Schema.Types.ObjectId;
var StateSchema = new Schema({
name: { type: String, required: true },
country: {type: ObjectId, ref: "Country"},
activeStatus: Boolean,
createdOn: Date,
updatedOn: Date
});
Here I am using pointing to my other schema with the help of ref.