Mongoose Schema

This post is about working with a database Schema with mongodb, using mongoose as a mongodb client. A Schema can be thought of as a blueprint of sorts for a Model that will be used to create many instances of said Model that will compose a collection. So in other words a Shema is a formal way of setting up the format of a database item, mainly its properties, and what types each property should be. This post will be a quick overview of how to define and use a Schema in with mongoose.

1 - What to know

This post is about making a Schema with mongoose the mongodb client. I am not going to get into detail about everything there is to write about with models, and mongodb here, just some basics with a Schema.

2 - A User Model Example of a Schema in mongoose

For an example of a Schema I will be writing about a Schema that I am making for a current project that is used for the User model. This Schema, the Model that uses it, and the project as a whole is a work in progress, but it should still serve well as a basic example of a Schema.

2.1 - Basic Schema example

So here is a basic example of a Schema in mongoose.

// grab mongoose
let mongoose = require('mongoose'),
Schema = mongoose.Schema;
 
// the User Schema
 
let UserSchema = new Schema({
        name: String,
        password: String,
        createDate: Date,
        lastOn: Date
    });

I start out by grabbing a reference to mongoose, and then Schema constructor. I then use the Schema constructor to create an instance of Schema. In doing so I pass the Schema constructor an object that contains the names of all the properties that define an instance of the Model that will use this Schema. In this object at a minimum contains the constructors that will be used for each property, but it can be more than that of course.

2.2 - Setting defaults for properties

It might be desirable to set some default values for each property in the Schema. This can be done by giving an object that contains a property called type that will then have the constructor that is used like before, but now I can add an additional property called default, and as the name suggests, yes this can be used to define what default values should be fore each property in the Schema.

// grab mongoose
let mongoose = require('mongoose'),
Schema = mongoose.Schema;
 
// the User Schema
 
let UserSchema = new Schema({
        name: { type: String, default: '_none'},
        password: { type: String, default: '1234'},
        createDate: { type: Date, default: Date.now},
        lastOn: { type: Date, default: Date.now}
    });

2.3 - Some pre save middleware hooks

it is possible to define some pre save middleware than can be used to do things like sanitation checks. For example I can have some pre save middleware that will throw an exception if a username is left at default, or has a value that evaluates to false. After that I can call next, or return a promise, and have another middleware that preforms another check and so on.

// Must have a name
UserSchema.pre('save', function (next) {
 
    let e = null;
 
    if (this.name === '_none' || !this.name) {
 
        e = new Error('name equals the default value _none, or evaluates to false');
 
    }
 
    next(e);
 
});
 
// The name must begin with a lowercase letter, and can not be longer than ten chars
UserSchema.pre('save', function (next) {
 
    let e = null;
 
    if (!this.name.match(/^[a-d]/) || this.name.length > 10) {
 
        e = new Error('must begin with a lowercase letter');
 
    }
 
    next(e);
 
});

Schema middleware is pretty useful, and these kinds of checks should be preformed to help keep things clean and sane in a deployment.

2.4 - Static methods

It is possible to define static methods that can then be used when working with the model elsewhere. I do so by appending the method to the statics object of a Schema instance. This differs from defining methods that apply to a single instance of a Model, as these methods apply to the whole collection.

// find by name
UserSchema.statics.findByName = function (name, cb) {
 
    return this.find({
        name: name
    }, cb);
 
};