Managing files

Marten gives you the ability to associate uploaded files with model records and to fully customize how and where those files are persisted. This section covers the basics of using files with models, how to interact with file objects, and introduces the concept of file storage.

Using files with models

You can make use of the file field when defining models: this allows to associate an uploaded file with specific model records.

For example, let's consider the following model:

class Attachment < Marten::Model
  field :id, :big_int, primary_key: true, auto: true
  field :file, :file, blank: false, null: false
end

Any Attachment model record will have a file attribute allowing interacting with the attached file:

attachment = Attachment.first!
attachment.file           # => #<Marten::DB::Field::File::File:0x102dd0ac0 ...>
attachment.file.attached? # => true
attachment.file.name      # => "test.txt"
attachment.file.size      # => 5796929
attachment.file.url       # => "/media/test.txt"

The object returned by the Attachment#file method is a "file object": an instance of Marten::DB::Field::File::File. These objects and their associated capabilities are described below in File objects.

Under which path are files persisted?

Files are stored at the root of the media storage by default. It should be noted that the path used to persist files in storages can be configured by setting the upload_to file field option.

For example, the previous Attachment model could be rewritten as follows to ensure that files are persisted in a foo/bar folder:

class Attachment < Marten::Model
  field :id, :big_int, primary_key: true, auto: true
  field :file, :file, blank: false, null: false, upload_to: "foo/bar"
end

It should also be noted that upload_to can correspond to a proc that takes the name of the file to save, which can be used to implement more complex file path generation logic if necessary:

class Attachment < Marten::Model
  field :id, :big_int, primary_key: true, auto: true
  field :file, :file, blank: false, null: false, upload_to: ->(name : String) { File.join("files/uploads", name) }
end

It should be noted that saving a model record will automatically result in any associated files being saved and persisted in the right storage automatically. For example, the following snippet reads a locally available file and attaches it to a new model record:

attachment = Attachment.new

File.open("test.txt") do |file|
  attachment.file = file
  attachment.save!
end

info

You don't need to take care of possible collisions between attached file names: Marten automatically ensures that uploaded files have a unique file name in the destination storage in order to avoid possible conflicts.

File objects

As mentioned previously, file objects are used internally by Marten to allow interacting with files that are associated with model records. These objects are instances of the Marten::DB::Field::File::File class. They give access to basic file properties and they allow to interact with the associated IO.

It should be noted that these "file objects" are always associated with a model record (persisted or not), and as such, they are only used in the context of the file model field.

Finally, it's worth mentioning that file objects can be attached and/or committed:

• an attached file object has an associated file set: in that case, its #attached? method returns true
• a committed file object has an associated file that is persisted to the underlying storage: in that case, its #committed? method returns true

For example:

attachment = Attachment.last!
attachment.file.attached?  # => true
attachment.file.committed? # => true

Accessing file properties

File objects give access to basic file properties through the use of the following methods:

Method	Description
#file	Returns the associated / "wrapped" file object. This can be a real File object, an uploaded file (instance of Marten::HTTP::UploadedFile), or nil if no file is associated yet.
#name	Returns the name of the file.
#size	Returns the size of the file, using the associated storage.
#url	Returns the URL of the file, using the associated storage.

Accessing the underlying file content

File objects allow you to access the underlying file content through the use of the #open method. This method returns an IO object.

For example:

attachment = Attachment.last!
file_io = attachment.file.open
puts file_io.gets_to_end

Updating the attached file

It is possible to update the actual file of a "file object" by using the #save method. This method allows saving the content of a specified IO object and associating it with a specific file path in the underlying storage.

For example:

attachment = Attachment.new

File.open("test.txt") do |file|
  attachment.file.save("path/to/test.txt", file)
  attachment.save!
end

attachment.file.url # => "/media/path/to/test.txt"

Deleting the attached file

It is also possible to manually "delete" the file associated with the "file object". To do so, the #delete method can be used. It should be noted that calling this method will remove the association between the model record and the file AND will also delete the file in the considered storage.

For example:

attachment = Attachment.last!
attachment.file.delete
attachment.file.attached?  # => false
attachment.file.committed? # => false

File storages

Marten uses a file storage mechanism to perform file operations like saving files, deleting files, generating URLs, ... This file storages mechanism allows to save files in different backends by leveraging a standardized API (eg. in the local file system, in a cloud bucket, etc).

By default, file model fields make use of the configured "media" storage. This storage uses the settings.media_files settings to determine what storage backend to use, and where to persist files. By default, the media storage uses the Marten::Core::Store::FileSystem storage backend, which ensures that files are persisted in the local file system, where the Marten application is running.

Interacting with the media file storage

You won't usually need to interact directly with the file storage, but it's worth mentioning that storage objects share the same API. Indeed, the class of these storage objects must inherit from the Marten::Core::Storage::Base abstract class and implement a set of mandatory methods which provide the following functionalities:

• saving files (#save)
• deleting files (#delete)
• opening files (#open)
• verifying that files exist (#exist?)
• retrieving file sizes (#size)
• retrieving file URLs (#url)

These capabilities are highlighted with the following example, where the media storage is used to interact with files:

file = File.open("test.txt")
storage = Marten.media_files_storage

filepath = storage.save("test.txt", file)
storage.exists?(filepath)  # => true
storage.exists?("unknown") # => false
storage.size(filepath)     # => 13
storage.url(filepath)      # => "/media/test_c43ba020.txt"
storage.delete(filepath)   # => nil
storage.exists?(filepath)  # => false

It should be noted that everything in the previous example could be done with a custom storage initialized manually as well:

file = File.open("test.txt")
storage = Marten::Core::Storage::FileSystem.new(root: "/tmp", base_url: "/tmp")

filepath = storage.save("test.txt", file)
storage.exists?(filepath)  # => true
storage.exists?("unknown") # => false
storage.size(filepath)     # => 13
storage.url(filepath)      # => "/tmp/test.txt"
storage.delete(filepath)   # => nil
storage.exists?(filepath)  # => false

Using a different storage with models

As mentioned previously, file model fields make use of the configured "media" storage by default. That being said, it is possible to leverage the storage option in order to make use of another storage if necessary.

For example:

custom_storage = Marten::Core::Storage::FileSystem.new(root: "/tmp", base_url: "/tmp")

class Attachment < Marten::Model
  field :id, :big_int, primary_key: true, auto: true
  field :file, :file, blank: false, null: false, storage: custom_storage
end

When doing this, all the file operations will be done using the configured storage instead of the default media storage.

Serving uploaded files during development

Marten provides a handler that you can use to serve media files in development environments only. This handler (Marten::Handlers::Defaults::Development::ServeMediaFile) is automatically mapped to a route when creating new projects through the use of the new management command:

Marten.routes.draw do
  # Other routes...

  if Marten.env.development?
    path "#{Marten.settings.media_files.url}<path:path>", Marten::Handlers::Defaults::Development::ServeMediaFile, name: "media_file"
  end
end

As you can see, this route will automatically use the URL that is configured as part of the url media files setting. For example, this means that a foo/bar.txt media file would be served by the /media/foo/bar.txt route in development if the url setting is set to /media/.

warning

It is very important to understand that this handler should only be used in development environments. Indeed, the Marten::Handlers::Defaults::Development::ServeMediaFile handler is not suited for production environments as it is not really efficient or secure. A better way to serve uploaded files is to leverage a web server or a cloud bucket for example (depending on the configured media files storage).