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POMongoose schema inheritance and model populate
 

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  1. POMongoose schema inheritance and model populate
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    <p>I have been trying this with the built in inheritance features of mongoose (rather than the extend plugin) but haven't been having much luck so far. This is a simplified example of code I am trying to use which exhibits the same problem. This is based on an expanded version of the mongoose documentation for schema inheritance using discriminators - <a href="http://mongoosejs.com/docs/api.html#model_Model.discriminator">http://mongoosejs.com/docs/api.html#model_Model.discriminator</a></p> <pre><code>var util = require('util'); var mongoose = require('mongoose'); mongoose.connect('mongodb://localhost/problem'); var Schema = mongoose.Schema; var ObjectId = Schema.ObjectId; function BaseSchema() { Schema.apply(this, arguments); this.add({ name: String, createdAt: Date }); } util.inherits(BaseSchema, Schema); var BossStatusSchema = new Schema({ status: String }); var BossStatus = mongoose.model('BossStatus', BossStatusSchema); var PersonSchema = new BaseSchema(); var Person = mongoose.model('Person', PersonSchema); var BossSchema = new BaseSchema({ department: String, bossStatus: { type: ObjectId, ref: 'BossStatus' } }); var Boss = Person.discriminator('Boss', BossSchema); </code></pre> <p>Example code to add the documents:</p> <pre><code>var superBoss = new BossStatus({ status: 'super' }); var normalBoss = new BossStatus({ status: 'normal' }); var andy = new Person({ name: 'Andy' }); var billy = new Boss({ name: 'Billy', bossStatus: superBoss._id }); var callback = function(err, result) { console.dir(err); console.dir(result); }; superBoss.save(callback); normalBoss.save(callback); andy.save(callback); billy.save(callback); </code></pre> <p>So when finding a record <strong>without</strong> populate:</p> <pre><code>Person .findOne({ name: 'Billy' }) .exec(callback); </code></pre> <p>The result is as expected, the bossStatus refers to an _id from the bossstatuses collection:</p> <pre><code>null { name: 'Billy', bossStatus: 52a20ab0185a7f4530000001, _id: 52a20ab0185a7f4530000004, __v: 0, __t: 'Boss' } </code></pre> <p>When adding the populate call:</p> <pre><code>Person .findOne({ name: 'Billy' }) .populate('bossStatus') .exec(callback); </code></pre> <p>The resulting bossStatus property of the Person result is <strong>null</strong>:</p> <pre><code>null { name: 'Billy', bossStatus: null, _id: 52a20ab0185a7f4530000004, __v: 0, __t: 'Boss' } </code></pre> <p>EDIT:</p> <p>Ok I've just put together what is probably a better example of what I'm trying to achieve, the schema structure lends itself more to a relational DB but hopefully makes the problem clearer.</p> <pre><code>var util = require('util'); var mongoose = require('mongoose'); mongoose.connect('mongodb://localhost/problem'); var Schema = mongoose.Schema; var ObjectId = Schema.ObjectId; function BaseSchema() { Schema.apply(this, arguments); this.add({ name: { type: String, unique: true, required: true } }); } util.inherits(BaseSchema, Schema); var DeviceSchema = new BaseSchema(); var LocalDeviceSchema = new BaseSchema({ driver: { type: ObjectId, ref: 'Driver' } }); var RemoteDeviceSchema = new BaseSchema({ networkAddress: { type: ObjectId, ref: 'NetworkAddress' } }); var DriverSchema = new Schema({ name: { type: String, unique: true, required: true } }); var NetworkHostSchema = new Schema({ host: { type: String, unique: true, required: true } }); var NetworkAddressSchema = new Schema({ networkHost: { type: ObjectId, ref: 'NetworkHost' }, port: { type: Number, min: 1, max: 65535 } }); var Driver = mongoose.model('Driver', DriverSchema); var NetworkHost = mongoose.model('NetworkHost', NetworkHostSchema); var NetworkAddress = mongoose.model('NetworkAddress', NetworkAddressSchema); var Device = mongoose.model('Device', DeviceSchema); var LocalDevice = Device.discriminator('LocalDevice', LocalDeviceSchema); var RemoteDevice = Device.discriminator('RemoteDevice', RemoteDeviceSchema); var networkHost = new NetworkHost({ host: '192.168.2.1' }); var networkAddress = new NetworkAddress({ networkHost: networkHost._id, port: 3000 }); var remoteDevice = new RemoteDevice({ name: 'myRemoteDevice', networkAddress: networkAddress._id }); var driver = new Driver({ name: 'ftdi' }); var localDevice = new LocalDevice({ name: 'myLocalDevice', driver: driver._id }); var callback = function(err, result) { if(err) { console.log(err); } console.dir(result); }; /* // Uncomment to save documents networkHost.save(function() { networkAddress.save(function() { remoteDevice.save(callback); }); }); driver.save(function() { localDevice.save(callback); }); */ var deviceCallback = function(err, device) { if(err) { console.log(err); } switch(device.__t) { case 'LocalDevice': console.log('Would create a local device instance passing populated result'); break; case 'RemoteDevice': console.log('Would create a remote device instance passing populated result'); break; } }; Device .findOne({name: 'myLocalDevice'}) .populate('driver') .exec(deviceCallback); </code></pre> <p>The LocalDevice and RemoteDevice schemas could (and probably would) include other differences.. The switch would for example use a DeviceFactory or something to create the instances. My thinking was it should be possible to search the devices table for a device by 'name' and populate the collection references (if this is the correct terminology?) without having to specify the collection to search in - this was my understanding of the point of schema inheritance - or have I completely misunderstood?</p> <p>Thanks for replies so far!</p>
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