#
Mongoose

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## Schemas

If you haven't yet done so, please take a minute to read the quickstart to get an idea of how Mongoose works.

This page covers `Schema` definition, plugins, instance methods, statics, indexes, virtuals and options. Let's start with `Schema` definition.

### Defining your schema

Everything in Mongoose starts with a Schema. Each schema maps to a MongoDB collection and defines the shape of the documents within that collection.

    var blogSchema = new Schema({
      title:  String,
      author: String,
      body:   String,
      comments: [{ body: String, date: Date }],
      date: { type: Date, default: Date.now },
      hidden: Boolean,
      meta: {
        votes: Number,
        favs:  Number
      }
    })

If you want to add additional keys later, use the Schema#add method.

Each key in our `blogSchema` defines a property in our documents which will be cast to its associated SchemaType. Keys may also be assigned nested objects containing further key/type definitions (e.g. the `meta` property above). For example, we've defined a `title` which will be cast to the String SchemaType and `date` which will be cast to a `Date` SchemaType.

The permitted SchemaTypes are

- String
- Number
- Date
- Buffer
- Boolean
- Mixed
- ObjectId
- Array

Read more about them here.

Schemas not only define the structure of your document and casting of properties, they also define document instance methods, static Model methods, compound indexes and document lifecycle hooks called middleware.

### Pluggable

Schemas are pluggable which allows us to package up reusable features into plugins that can be shared with the community or just between your projects.

### Instance methods

Models are just fancy `constructor` functions. As such they can have prototype methods inherited by their instances. In the case of Mongoose, instances are documents.

Defining an instance method is easy.

    var animalSchema = new Schema({ name: String, type: String });

    animalSchema.methods.findSimilarTypes = function (cb) {
      return this.model('Animal').find({ type: this.type }, cb);
    }

Now all of our `animal` instances have a `findSimilarTypes` method available to it.

    var Animal = mongoose.model('Animal', animalSchema);
    var dog = new Animal({ type: 'dog' })

    dog.findSimilarTypes(function (err, dogs) {
      console.log(dogs) // woof
    })

### Statics

Adding static constructor methods to Models is simple as well. Continuing with our `animalSchema`:

    animalSchema.statics.findByName = function (name, cb) {
      this.find({ name: new RegExp(name, 'i'), cb);
    }

    var Animal = mongoose.model('Animal', animalSchema);
    Animal.findByName('fido', function (err, animals) {
      console.log(animals);
    })

### Indexes

Indexes can be defined at the path level or the `schema` level. Defining indexes at the schema level is necessary when defining compound indexes.

    animalSchema.index({ name: 1, type: -1 });

When your application starts up, Mongoose automatically calls `ensureIndex` for each defined index. This behavior can be disabled by setting the `autoIndex` option of your schema to false.

    animalSchema.set('autoIndex', false)
    // or
    new Schema({..}, { autoIndex: false })

See also the `Model#ensureIndexes` method.

### Virtuals

Virtual attributes are attributes that are convenient to have around but that do not get persisted to MongoDB.

    var personSchema = new Schema({
      name: {
        first: String,
        last: String
      }
    });

    var Person = mongoose.model('Person', personSchema);

    var bad = new Person({
        name: { first: 'Walter', last: 'White' }
    });

Suppose we want to log the full name of `bad`. We could do this manually like so:

    console.log(bad.name.first + ' ' + bad.name.last); // Walter White

Or we could add a `virtual` attribute getter to our `personSchema` so we don't need to write out this string concatenation mess each time:

    personSchema.virtual('name.full').get(function () {
      return this.name.first + ' ' + this.name.last;
    })

Now, when we access our virtual full name property, our getter function will be invoked and the value returned:

    console.log('%s is insane', bad.name.full) // Walter White is insane

It would also be nice to be able to set `this.name.first` and `this.name.last` by setting `this.name.full`. For example, if we wanted to change `bad`'s `name.first` and `name.last` to 'Breaking' and 'Bad' respectively, it'd be nice to just:

    bad.name.full = 'Breaking Bad';

Mongoose let's you do this as well through its virtual attribute setters:

    personSchema.virtual('name.full').set(function (name) {
      var split = name.split(' ');
      this.name.first = split[0];
      this.name.last = split[1];
    })

    ...

    mad.name.full = 'Breaking Bad';
    console.log(mad.name.first) // Breaking

If you need attributes that you can get and set but that are not themselves persisted to MongoDB, virtual attributes is the Mongoose feature for you.

### Options

`Schema`s have a few configurable options which can be passed to the constructor or `set` directly:

    new Schema({..}, options);

    // or

    var schema = new Schema({..});
    schema.set(option, value);

Valid options:

- safe
- strict
- capped
- versionKey
- autoIndex

#### option: safe

This option is passed to MongoDB with all operations and let's us specify if errors should be returned to our callbacks as well as tune write behavior.

    var safe = true;
    new Schema({ .. }, { safe: safe })

By default this is set to `true` for all schemas which guarentees that any occurring error gets passed back to our callback. By setting `safe` to something else like `{ j: 1, w: 2, wtimeout: 10000 }` we can guarantee the write was committed to the MongoDB journal (j: 1), at least 2 replicas (w: 2), and that the write will timeout if it takes longer than 10 seconds (wtimeout: 10000). Errors will still be passed to our callback.

There are other write concerns like `{ w: "majority" }` too. See the MongoDB docs for more details.

    var safe = { w: "majority", wtimeout: 10000 };
    new Schema({ .. }, { safe: safe })

#### option: strict

The strict option, (enabled by default), ensures that values added to our model instance that were not specified in our schema do not get saved to the db. NOTE: do not set to false unless you have good reason.

    var thingSchema = new Schema({..})
    var Thing = db.model('Thing', schemaSchema);
    var thing = new Thing({ iAmNotInTheSchema: true });
    thing.save() // iAmNotInTheSchema is not saved to the db

    // set to false..
    var thingSchema = new Schema({..}, { strict: false });
    var thing = new Thing({ iAmNotInTheSchema: true });
    thing.save() // iAmNotInTheSchema is now saved to the db!!

This value can be overridden at the model instance level by passing a second boolean argument:

    var Thing = db.model('Thing');
    var thing = new Thing(doc, true);  // enables strict mode
    var thing = new Thing(doc, false); // disables strict mode

The `strict` option may also be set to `"throw"` which will cause errors to be produced instead of ignoring the bad data.

NOTE: in mongoose v2 the default was false.

#### option: shardKey

The `shardKey` option is used when we have a sharded MongoDB architecture. Each sharded collection is given a shard key which must be present in all insert/update operations. We just need to set this schema option to the same shard key and we’ll be all set.

    new Schema({ .. }, { shardkey: { tag: 1, name: 1 }})

Note that Mongoose does not send the `shardcollection` command for you. You must configure your shards yourself.

#### option: capped

Mongoose supports MongoDBs capped collections. To specify the underlying MongoDB collection be `capped`, set the `capped` option to the maximum size of the collection in bytes.

    new Schema({..}, { capped: 1024 })

The `capped` option may also be set to an object if you want to pass additional options like max or autoIndexId. In this case you must explicitly pass the `size` option which is required.

    new Schema({..}, { capped: { size: 1024, max: 1000, autoIndexId: true })

#### option: versionKey

The `versionKey` is a property set on each document when first created by Mongoose. This keys value contains the internal revision of the document. The name of this document property is configurable. The default is `__v`. If this conflicts with your application you can configure as such:

    var schema = new Schema({ name: 'string' });
    var Thing = db.model('Thing', schema);
    var thing = new Thing({ name: 'mongoose v3' });
    thing.save(); // { __v: 0, name: 'mongoose v3' }

    // customized versionKey
    new Schema({..}, { versionKey: '_somethingElse' })
    var Thing = db.model('Thing', schema);
    var thing = new Thing({ name: 'mongoose v3' });
    thing.save(); // { _somethingElse: 0, name: 'mongoose v3' }

Document versioning can also be disabled by setting the `versionKey` to false. DO NOT disable versioning unless you know what you are doing.

    new Schema({..}, { versionKey: false })
    var Thing = db.model('Thing', schema);
    var thing = new Thing({ name: 'no versioning please' });
    thing.save(); // { name: 'no versioning please' }

#### option: autoIndex

At application startup, Mongoose sends an `ensureIndex` command for each index declared in your `Schema`. As of Mongoose v3, indexes are created in the `background` by default. If you wish to disable the auto-creation feature and manually handle when indexes are created, set your `Schema`s `autoIndex` option to `false` and use the ensureIndexes method on your model.

    var schema = new Schema({..}, { autoIndex: false })
    var Clock = db.model('Clock', schema);
    Clock.ensureIndexes(callback);