Persistence¶

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Standard
Atomic
Custom

Mongoid supports all expected CRUD operations for those familiar with other Ruby mappers like Active Record or Data Mapper. What distinguishes Mongoid from other mappers for MongoDB is that the general persistence operations perform atomic updates on only the fields that have changed instead of writing the entire document to the database each time.

The persistence sections will provide examples on what database operation is performed when executing the documented command.

Standard¶

Mongoid’s standard persistence methods come in the form of common methods you would find in other mapping frameworks. The following table shows all standard operations with examples.

Operation	Example
`Model.create` Insert a document or multiple documents into the database.	copy Person.create( first_name: "Heinrich", last_name: "Heine" ) Person.create([ { first_name: "Heinrich", last_name: "Heine" }, { first_name: "Willy", last_name: "Brandt" } ]) Person.create(first_name: "Heinrich") do \|doc\| doc.last_name = "Heine" end
`Model.create!` Insert a document or multiple documents into the database, raising an error if a validation error occurs.	copy Person.create!( first_name: "Heinrich", last_name: "Heine" ) Person.create!([ { first_name: "Heinrich", last_name: "Heine" }, { first_name: "Willy", last_name: "Brandt" } ]) Person.create!(first_name: "Heinrich") do \|doc\| doc.last_name = "Heine" end
`Model#save` Saves the changed attributes to the database atomically, or insert the document if flagged as a new record via `Model#new_record?` . Can bypass validations if wanted.	copy person = Person.new( first_name: "Heinrich", last_name: "Heine" ) person.save person.save(validate: false) person.first_name = "Christian Johan" person.save
`Model#save!` Saves the changed attributes to the database atomically, or insert the document if new. Will raise an error of validations fail.	copy person = Person.new( first_name: "Heinrich", last_name: "Heine" ) person.save! person.first_name = "Christian Johan" person.save!
`Model#update_attributes` Update the document attributes in the database. Will return true if validation passed, false if not.	copy person.update_attributes( first_name: "Jean", last_name: "Zorg" )
`Model#update_attributes!` Update the document attributes in the database and raise an error if validation failed.	copy person.update_attributes!( first_name: "Leo", last_name: "Tolstoy" )
`Model#update_attribute` Update a single attribute, bypassing validations.	copy person.update_attribute(:first_name, "Jean")
`Model#upsert` Performs a MongoDB upsert on the document. If the document exists in the database, it will get overwritten with the current attributes of the document in memory. If the document does not exist in the database, it will be inserted. Note that this only runs the `{before\|after\|around}_upsert` callbacks.	copy person = Person.new( first_name: "Heinrich", last_name: "Heine" ) person.upsert
`Model#touch` Update the document’s updated_at timestamp, optionally with one extra provided time field. This will cascade the touch to all `belongs_to` relations of the document with the option set. This operation skips validations and callbacks.	copy person.touch person.touch(:audited_at)
`Model#delete` Deletes the document from the database without running callbacks.	copy person.delete
`Model#destroy` Deletes the document from the database while running destroy callbacks.	copy person.destroy
`Model.delete_all` Deletes all documents from the database without running any callbacks.	copy Person.delete_all
`Model.destroy_all` Deletes all documents from the database while running callbacks. This is a potentially expensive operation since all documents will be loaded into memory.	copy Person.destroy_all

Atomic¶

Although Mongoid performs atomic operations under the covers by default, there may be cases where you want to do this explicitly without persisting other fields. Mongoid provides support for all of these operations as well. When executing atomic operations via these methods, no callbacks will ever get run, nor will any validations.

Operation	Example
`Model#add_to_set` Performs an atomic $addToSet on the field.	copy person.add_to_set(aliases: "Bond")
`Model#bit` Performs an atomic $bit on the field.	copy person.bit(age: { and: 10, or: 12 })
`Model#inc` Performs an atomic $inc on the field.	copy person.inc(age: 1)
`Model#pop` Performs an atomic $pop on the field.	copy person.pop(aliases: 1)
`Model#pull` Performs an atomic $pull on the field.	copy person.pull(aliases: "Bond")
`Model#pull_all` Performs an atomic $pullAll on the field.	copy person.pull_all(aliases: [ "Bond", "James" ])
`Model#push` Performs an atomic $push on the field.	copy person.push(aliases: ["007","008"])
`Model#rename` Performs an atomic $rename on the field.	copy person.rename(bday: :dob)
`Model#set` Performs an atomic $set on the field.	copy person.set(name: "Tyler Durden")
`Model#unset` Performs an atomic $unset on the field.	copy person.unset(:name)

Persistence Context Attributes¶

Mongoid provides client_name, database_name and collection_name methods on model classes to determine the client, database and collection names used for persistence:

copy

Band.client_name
# => :default

Band.database_name
# => "mongoid"

Band.collection_name
# => :bands

Custom¶

There may be cases where you want to persist documents to different sources from their defaults, or with different options from the default. Mongoid provides run-time support for this as well as support on a per-model basis.

On a per-model basis, you can tell it to store in a custom collection name, a different database, or a different client. The following example would store the Band class by default into a collection named “artists” in the database named “music”, with the client “secondary”.

Note that the value supplied to the client option must be configured under clients in your mongoid.yml.

copy

class Band
  include Mongoid::Document
  store_in collection: "artists", database: "music", client: "secondary"
end

If no store_in macro would have been provided, Mongoid would store the model in a collection named “bands” in the default database in the default client.

It is possible to change the client, database and collection, as well as any of the MongoDB client options, used for persistence for a group of operations by using the with method on a model class or instance:

copy

Band.with(database: "music-non-stop") do |klass|
  klass.create(...)

  band = Band.first

  Band.create(...)
end

Band.with(collection: "artists") do |klass|
  klass.delete_all

  Band.delete_all
end

band.with(client: :tertiary) do |band_object|
  band_object.save!

  band.save!
end

The with method creates a temporary persistence context and a MongoDB client to be used for operations in the context. For the duration of the block, the persistence context on the model class or instance that with was called on is changed to the temporary persistence context. For convenience, the model class or instance that with was called on is yielded to the block.

The temporary persistence context applies to both queries and writes.

Care should be taken when performing persistence operations across different persistence contexts. For example, if a document is saved in a temporary persistence context, it may not exist in the default persistence context, failing subsequent updates:

copy

band = Band.new(name: "Scuba")
band.with(collection: "artists") do |band_object|
  band_object.save!
end

# This will not save - updates the collection "bands" which does not have
# the Scuba band
band.update_attribute(likes: 1000)

# This will update the document.
band.with(collection: "artists") do |band_object|
  band_object.update_attribute(likes: 1000)
end

As of Mongoid 6.0, the with method must always be called with a block, and the temporary persistence context exists only for the duration of the block. This is because a new client is created under the covers with the options passed to with. To ensure that this client is closed and its associated resources are freed, the scope when this client could be used must be well-defined.

If you want to switch the persistence context for all operations at runtime, but don’t want to be using with all over your code, Mongoid provides the ability to do this as the client and database level globally. The methods for this are Mongoid.override_client and Mongoid.override_database. A useful case for this are internationalized applications that store information for different locales in different databases or clients, but the schema in each remains the same.

copy

class BandsController < ApplicationController
  before_filter :switch_database
  after_filter :reset_database

  private

  def switch_database
    I18n.locale = params[:locale] || I18n.default_locale
    Mongoid.override_database("my_db_name_#{I18n.locale}")
  end

  def reset_database
    Mongoid.override_database(nil)
  end
end

In the above example, all persistence operations would be stored in the alternative database for all remaining operations on this thread. This is why the after request set the override back to nil - it ensures subsequent requests with no local params use the default option.

If you want to drop down to the driver level to perform operations, you can grab the Mongo client or collection from the model or document instance:

copy

Band.mongo_client
band.mongo_client
Band.collection
band.collection

From here you also have the same runtime persistence options using the client’s #with:

copy

client = Band.mongo_client.with(write: { w: 0 }, database: "musik")
client[:artists].find(...)

You can also override the :read or :write options on the collection using the collections #with:

copy

collection_w_0 = Band.collection.with(write: { w: 0 })
collection_w_0[:artists].find(...)

Mongoid does not provide a mechanism for creating capped collections on the fly - you will need to create these yourself one time up front either with the driver or via the Mongo console.

To create a capped collection with the driver:

copy

client["name", :capped => true, :size => 1024].create

To create a capped collection from the Mongo console:

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db.createCollection("name", { capped: true, size: 1024 });

Mongoid does not provide a mechanism for creating a collection with a default collation. Like capped collections, you will need to create the collection yourself one time, up-front, either with the driver or via the Mongo console.

To create a collection with a default collation with the driver:

copy

client["name", :collation => { :locale => 'fr'}].create

To create a collection with a default collation from the Mongo console:

copy

db.createCollection("name", { collation: { locale: 'fr' } });

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