*************** CRUD Operations *************** .. default-domain:: mongodb .. contents:: On this page :local: :backlinks: none :depth: 2 :class: singlecol Saving Documents ================ 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. .. list-table:: :header-rows: 1 :widths: 30 60 * - Operation - Example * - ``Model.create!`` *Insert a document or multiple documents into the database, raising an error if a validation or server error occurs.* *Pass a hash of attributes to create one document with the specified attributes, or an array of hashes to create multiple documents. If a single hash is passed, the corresponding document is returned. If an array of hashes is passed, an array of documents corresponding to the hashes is returned.* *If a block is given to* ``create!`` *, it will be invoked with each document as the argument in turn prior to attempting to save that document.* *If there is a problem saving any of the documents, such as a validation error or a server error, an exception is raised and, consequently, none of the documents are returned. However, if an array of hashes was passed and previous documents were successfully saved, those documents will remain in the database.* - .. code-block:: ruby Person.create!( first_name: "Heinrich", last_name: "Heine" ) # => Person instance Person.create!([ { first_name: "Heinrich", last_name: "Heine" }, { first_name: "Willy", last_name: "Brandt" } ]) # => Array of two Person instances Person.create!(first_name: "Heinrich") do |doc| doc.last_name = "Heine" end # => Person instance * - ``Model.create`` *Instantiate a document or multiple documents and, if validations pass, insert them into the database.* ``create`` *is similar to* ``create!`` *but does not raise exceptions on validation errors. It still raises errors on server errors, such as trying to insert a document with an* ``_id`` *that already exists in the collection.* *If any validation errors are encountered, the respective document is not inserted but is returned along with documents that were inserted. Use* ``persisted?`` *,* ``new_record?`` *or* ``errors`` *methods to check which of the returned documents were inserted into the database.* - .. code-block:: ruby Person.create( first_name: "Heinrich", last_name: "Heine" ) # => Person instance Person.create([ { first_name: "Heinrich", last_name: "Heine" }, { first_name: "Willy", last_name: "Brandt" } ]) # => Array of two Person instances Person.create(first_name: "Heinrich") do |doc| doc.last_name = "Heine" end # => Person instance class Post include Mongoid::Document validates_uniqueness_of :title end posts = Post.create([{title: "test"}, {title: "test"}]) # => array of two Post instances posts.map { |post| post.persisted? } # => [true, false] * - ``Model#save!`` *Save the changed attributes to the database atomically, or insert the document if new. Raises an exception if validations fail or there is a server error.* *Returns true if the changed attributes were saved, raises an exception otherwise.* - .. code-block:: ruby person = Person.new( first_name: "Heinrich", last_name: "Heine" ) person.save! person.first_name = "Christian Johan" person.save! * - ``Model#save`` *Save the changed attributes to the database atomically, or insert the document if new.* *Returns true if the changed attributes were saved. Returns false if there were any validation errors. Raises an exception if the document passed validation but there was a server error during the save.* *Pass* ``validate: false`` *option to bypass validations.* *Pass* ``touch: false`` *option to ignore the updates to the updated_at field. If the document being save has not been previously persisted, this option is ignored and the created_at and updated_at fields will be updated with the current time.* - .. code-block:: ruby person = Person.new( first_name: "Heinrich", last_name: "Heine" ) person.save person.save(validate: false) person.save(touch: false) 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.* - .. code-block:: ruby 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.* - .. code-block:: ruby person.update_attributes!( first_name: "Leo", last_name: "Tolstoy" ) * - ``Model#update_attribute`` *Update a single attribute, bypassing validations.* - .. code-block:: ruby person.update_attribute(:first_name, "Jean") * - ``Model#upsert`` *Performs a MongoDB replace with upsert on the document. If the document exists in the database, it will get overwritten with the current document in the application (any attributes present in the database but not in the application's document instance will be lost). If the document does not exist in the database, it will be inserted. Note that this only runs the* ``{before|after|around}_upsert`` *callbacks.* - .. code-block:: ruby 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`` *associations of the document with the option set. This operation skips validations and callbacks.* *Attempting to touch a destroyed document will raise* ``FrozenError``, *same as if attempting to update an attribute on a destroyed document.* - .. code-block:: ruby person.touch person.touch(:audited_at) * - ``Model#delete`` *Deletes the document from the database without running callbacks.* *If the document is not persisted, Mongoid will attempt to delete from the database any document with the same* ``_id``. - .. code-block:: ruby person.delete person = Person.create!(...) unsaved_person = Person.new(id: person.id) unsaved_person.delete person.reload # raises Mongoid::Errors::DocumentNotFound because the person was deleted * - ``Model#destroy`` *Deletes the document from the database while running destroy callbacks.* *If the document is not persisted, Mongoid will attempt to delete from the database any document with the same* ``_id``. - .. code-block:: ruby person.destroy person = Person.create!(...) unsaved_person = Person.new(id: person.id) unsaved_person.destroy person.reload # raises Mongoid::Errors::DocumentNotFound because the person was deleted * - ``Model.delete_all`` *Deletes all documents from the database without running any callbacks.* - .. code-block:: ruby 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.* - .. code-block:: ruby Person.destroy_all Mongoid provides the following persistence-related attributes: .. list-table:: :header-rows: 1 :widths: 30 60 * - Attribute - Example * - ``Model#new_record?`` *Returns* ``true`` *if the model instance has not yet been saved to the database. Opposite of* ``persisted?`` - .. code-block:: ruby person = Person.new( first_name: "Heinrich", last_name: "Heine" ) person.new_record? # => true person.save! person.new_record? # => false * - ``Model#persisted?`` *Returns* ``true`` *if the model instance has been saved to the database. Opposite of* ``new_record?`` - .. code-block:: ruby person = Person.new( first_name: "Heinrich", last_name: "Heine" ) person.persisted? # => false person.save! person.persisted? # => true Atomic ------ Mongoid exposes :manual:`MongoDB update operators ` as methods on Mongoid documents. When these methods are used, callbacks are not invoked and validations are not performed. The supported update operators are: .. list-table:: :header-rows: 1 :widths: 30 60 * - Operation - Example * - ``Model#add_to_set`` *Performs an atomic $addToSet on the field.* - .. code-block:: ruby person.add_to_set(aliases: "Bond") * - ``Model#bit`` *Performs an atomic $bit on the field.* - .. code-block:: ruby person.bit(age: { and: 10, or: 12 }) * - ``Model#inc`` *Performs an atomic $inc on the field.* - .. code-block:: ruby person.inc(age: 1) * - ``Model#pop`` *Performs an atomic $pop on the field.* - .. code-block:: ruby person.pop(aliases: 1) * - ``Model#pull`` *Performs an atomic $pull on the field.* - .. code-block:: ruby person.pull(aliases: "Bond") * - ``Model#pull_all`` *Performs an atomic $pullAll on the field.* - .. code-block:: ruby person.pull_all(aliases: [ "Bond", "James" ]) * - ``Model#push`` *Performs an atomic $push on the field.* - .. code-block:: ruby person.push(aliases: ["007","008"]) * - ``Model#rename`` *Performs an atomic $rename on the field.* - .. code-block:: ruby person.rename(bday: :dob) * - ``Model#set`` *Updates an attribute on the model instance and, if the instance is already persisted, performs an atomic $set on the field, bypassing validations.* ``set`` *can also deeply set values on Hash fields.* ``set`` *can also deeply set values on* ``embeds_one`` *associations. If such an association's document is nil, one will be created prior to the update.* ``set`` *should not be used with* ``has_one`` *associations, as it does not correctly work in such cases.* - .. code-block:: ruby person = Person.create!(name: "Ricky Bobby") person.set(name: "Tyler Durden") # updates name in the database person = Person.new person.set(name: "Tyler Durden") # does not write to database person.name # => "Tyler Durden" person.persisted? # => true class Post include Mongoid::Document field :metadata, type: Hash end post = Post.create! post.set('metadata.published_at' => Time.now) post.metadata['published_at'] # => Time instance post.set('metadata.approved.today' => true) post.metadata['approved'] # => {'today' => true} class Flight include Mongoid::Document embeds_one :plan end class Plan include Mongoid::Document embedded_in :flight field :route, type: String end flight = Flight.create! flight.plan # => nil flight.set('plan.route', 'test route') flight.plan # => Plan instance flight.plan.route # => "test route" * - ``Model#unset`` *Performs an atomic $unset on the field.* - .. code-block:: ruby person.unset(:name) Note that, because these methods skip validations, it is possible to both save invalid documents into the database and end up with invalid documents in the application (which would subsequently fail to save via a ``save`` call due to the failing validations). .. _atomic-operation-grouping: Atomic Operation Grouping ````````````````````````` Atomic operations may be grouped together using the ``#atomically`` method on a document. All operations inside the block given to ``#atomically`` are sent to the cluster in a single atomic command. For example: .. code-block:: ruby person.atomically do person.inc(age: 1) person.set(name: 'Jake') end ``#atomically`` blocks may be nested. The default behavior is to write changes performed by each block as soon as the block ends: .. code-block:: ruby person.atomically do person.atomically do person.inc(age: 1) person.set(name: 'Jake') end raise 'An exception' # name and age changes are still persisted end This behavior can be changed by specifying the ``join_context: true`` option to ``#atomically``, or globally by setting the ``join_contexts`` :ref:`configuration option ` to ``true``. When context joining is enabled, nested ``#atomically`` blocks are joined with the outer blocks, and only the outermost block (or the first block where ``join_contexts`` is false) actually writes changes to the cluster. For example: .. code-block:: ruby person.atomically do person.atomically(join_context: true) do person.inc(age: 1) person.set(name: 'Jake') end raise 'An exception' # name and age changes are not persisted end The context joining behavior can be enabled globally by default by setting ``join_context`` option in Mongoid configuration. In this case specifying ``join_context: false`` on an ``#atomically`` block can be used to obtain the independent persistence context behavior. If an exception is raised in an ``#atomically`` block which has not yet persisted its changes to the cluster, any pending attribute changes on Mongoid models are reverted. For example: .. code-block:: ruby person = Person.new(name: 'Tom') begin person.atomically do person.inc(age: 1) person.set(name: 'Jake') person.name # => 'Jake' raise 'An exception' end rescue Exception person.name # => 'Tom' end Atomic operations described in this section apply to one document at a time, therefore nesting ``#atomically`` blocks invoked on multiple documents does not make changes to the different documents be persisted atomically together. However, MongoDB offers :ref:`multi-document transactions ` as of server version 4.0 which provide atomic persistence across multiple documents. Reloading ========= Use the ``reload`` method to fetch the most recent version of a document from the database. Any unsaved modifications to the document's attributes are lost: .. code-block:: ruby band = Band.create!(name: 'foo') # => # band.name = 'bar' band # => # band.reload # => # When a document is reloaded, all of its embedded associations are also reloaded in the same query (since embedded documents are stored in the parent document on the server). If a document has referenced associations, the loaded associations' are not reloaded but their values are cleared, such that these associations would be loaded from the database at the next access. .. note:: Some operations on associations, for example assignment, persists the new document. In these cases there may not be any unsaved modifications to revert by reloading. In the following example, the assignment of the empty array to the association is immediately persisted and reloading does not make any changes to the document: .. code-block:: ruby # Assuming band has many tours, which could be referenced: band = Band.create!(tours: [Tour.create!]) # ... or embedded: band = Band.create!(tours: [Tour.new]) # This writes the empty tour list into the database. band.tours = [] # There are no unsaved modifications in band at this point to be reverted. band.reload # Returns the empty array since this is what is in the database. band.tours # => [] If the model has a :ref:`shard key ` defined, the shard key value is included in the reloading query. If the database does not contain a matching document, Mongoid normally raises ``Mongoid::Errors::DocumentNotFound``. However, if the configuration option ``raise_not_found_error`` is set to ``false``, and the database does not contain a matching document, Mongoid replaces the current document with a newly created document whose attributes are set to default values. Importantly, this generally causes the ``_id`` of the document to change, as the following example demonstrates: .. code-block:: ruby band = Band.create! # => # Mongoid.raise_not_found_error = false band.destroy band.reload # => # For this reason, it is not recommended to use ``reload`` when ``raise_not_found_error`` is set to ``false``. Reloading Unsaved Documents --------------------------- ``reload`` can be called when the document has not yet been persisted. In this case ``reload`` performs a ``find`` query using the ``id`` value specified in the document (and the shard key value, if a shard key is defined): .. code-block:: ruby existing = Band.create!(name: 'Photek') # Unsaved document band = Band.new(id: existing.id) band.reload band.name # => "Photek" Accessing Field Values ====================== Mongoid provides several ways of accessing field values. .. note:: All of the access methods described below raise ``Mongoid::Errors::AttributeNotLoaded`` when the field being accessed is :ref:`projected out `, either by virtue of not being included in :ref:`only ` or by virtue of being included in :ref:`without `. This applies to both reads and writes. Getters & Setters ----------------- The recommended way is to use the getter and setter methods generated for each declared field: .. code-block:: ruby class Person include Mongoid::Document field :first_name end person = Person.new person.first_name = "Artem" person.first_name # => "Artem" To use this mechanism, each field must be explicitly declared, or the model class must enable :ref:`dynamic fields `. Custom Getters & Setters ------------------------ It is possible to explicitly define the getter and setter methods to provide custom behavior when reading or writing fields, for example value transformations or storing values under different field names. In this case ``read_attribute`` and ``write_attribute`` methods can be used to read and write the values directly into the attributes hash: .. code-block:: ruby class Person include Mongoid::Document def first_name read_attribute(:fn) end def first_name=(value) write_attribute(:fn, value) end end person = Person.new person.first_name = "Artem" person.first_name # => "Artem" person.attributes # => {"_id"=>BSON::ObjectId('606477dc2c97a628cf47075b'), "fn"=>"Artem"} .. _read-write-attribute: ``read_attribute`` & ``write_attribute`` ---------------------------------------- The ``read_attribute`` and ``write_attribute`` methods can be used explicitly as well. Note that if a field specifies its :ref:`storage field name `, both ``read_attribute`` and ``write_attribute`` accept either the declared field name or the storage field name for operations: .. code-block:: ruby class Person include Mongoid::Document field :first_name, as: :fn field :last_name, as: :ln end person = Person.new(first_name: "Artem") # => # person.read_attribute(:first_name) # => "Artem" person.read_attribute(:fn) # => "Artem" person.write_attribute(:last_name, "Pushkin") person # => # person.write_attribute(:ln, "Medvedev") person # => # ``read_attribute`` and ``write_attribute`` do not require that a field with the used name is defined, but writing field values with ``write_attribute`` does not cause the respective field to be defined either: .. code-block:: ruby person.write_attribute(:undefined, "Hello") person # => # person.attributes # => {"_id"=>BSON::ObjectId('60647b212c97a6292c195b4c'), "first_name"=>"Artem", "last_name"=>"Medvedev", "undefined"=>"Hello"} person.read_attribute(:undefined) # => "Hello" person.undefined # raises NoMethodError When ``read_attribute`` is used to access a missing field, it returns ``nil``. Hash Access ----------- Mongoid model instances define the ``[]`` and ``[]=`` methods to provide ``Hash`` style access to the attributes. ``[]`` is an alias for ``read_attribute`` and ``[]=`` is an alias for ``write_attribute``; see the section on :ref:`read_attribute and write_attribute ` for the detailed description of their behavior. .. code-block:: ruby class Person include Mongoid::Document field :first_name, as: :fn field :last_name, as: :ln end person = Person.new(first_name: "Artem") person["fn"] # => "Artem" person[:first_name] # => "Artem" person[:ln] = "Medvedev" person # => # person["last_name"] = "Pushkin" person # => # Bulk Attribute Writes --------------------- In cases where you want to set multiple field values at once, there are a few different ways of accomplishing this as well. .. code-block:: ruby # Get the field values as a hash. person.attributes # Set the field values in the document. Person.new(first_name: "Jean-Baptiste", middle_name: "Emmanuel") person.attributes = { first_name: "Jean-Baptiste", middle_name: "Emmanuel" } person.write_attributes( first_name: "Jean-Baptiste", middle_name: "Emmanuel", ) Dirty Tracking ============== Mongoid supports tracking of changed or "dirty" fields with an API that mirrors that of Active Model. If a defined field has been modified in a model the model will be marked as dirty and some additional behavior comes into play. Viewing Changes --------------- There are various ways to view what has been altered on a model. Changes are recorded from the time a document is instantiated, either as a new document or via loading from the database up to the time it is saved. Any persistence operation clears the changes. .. code-block:: ruby class Person include Mongoid::Document field :name, type: String end person = Person.first person.name = "Alan Garner" # Check to see if the document has changed. person.changed? # true # Get an array of the names of the changed fields. person.changed # [ :name ] # Get a hash of the old and changed values for each field. person.changes # { "name" => [ "Alan Parsons", "Alan Garner" ] } # Check if a specific field has changed. person.name_changed? # true # Get the changes for a specific field. person.name_change # [ "Alan Parsons", "Alan Garner" ] # Get the previous value for a field. person.name_was # "Alan Parsons" .. note:: Setting the associations on a document does not cause the ``changes`` or ``changed_attributes`` hashes to be modified. This is true for all associations whether referenced or embedded. Note that changing the _id(s) field on referenced associations does cause the changes to show up in the ``changes`` and the ``changed_attributes`` hashes. Resetting Changes ----------------- You can reset changes of a field to its previous value by calling the reset method. .. code-block:: ruby person = Person.first person.name = "Alan Garner" # Reset the changed name back to the original person.reset_name! person.name # "Alan Parsons" Persistence ----------- Mongoid uses dirty tracking as the core of its persistence operations. It looks at the changes on a document and atomically updates only what has changed, unlike other frameworks that write the entire document on each save. If no changes have been made, Mongoid will not hit the database on a call to ``Model#save``. Viewing Previous Changes ------------------------ After a document has been persisted, you can see what the changes were previously by calling ``Model#previous_changes``. .. code-block:: ruby person = Person.first person.name = "Alan Garner" person.save # Clears out current changes. # View the previous changes. person.previous_changes # { "name" => [ "Alan Parsons", "Alan Garner" ] } Updating Container Fields ========================= Be aware that, until `MONGOID-2951 `_ is resolved, all fields including container ones must be assigned to for their values to be persisted to the database. For example, adding to a set like this does not work: .. code-block:: ruby class Band include Mongoid::Document field :tours, type: Set end band = Band.new band.tours # => # band.tours << 'London' # => # band.tours # => # Instead, the field value must be modified outside of the model and assigned back to the model as follows: .. code-block:: ruby class Band include Mongoid::Document field :tours, type: Set end band = Band.new tours = band.tours # => # tours << 'London' # => # band.tours = tours # => # band.tours # => #