For whatever reason you need or choose to store blobs in databases. Yet, you do not wish to mix blob columns in the same table as your regular attributes. BinaryColumnTable helps you store ALL blobs in a separate table, managed transparently by an ActiveRecord model. Optionally, it helps you record the content-type of the blob.

This plugin does nothing else.

In your existing model, e.g. Member, declare your binary columns (note: these columns does not exist in your “members” table)

class Member < ActiveRecord::Base
  has_binary_columns :photo, :resume, :secret_zip
end

For that to work, generate a model called BinaryColumn to contain these blobs.

rails generate model BinaryColumn original_table_type:string original_table_id:integer name:string content_type:string original_filename:string content:binary

You may wish to edit the generated migration file to add a custom index to the bottom of the “self.up” method,

class CreateBinaryColumns < ActiveRecord::Migration
  def self.up
    create_table :binary_columns do |t|
      t.string :original_table_type
      t.integer :original_table_id
      t.string :name
      t.string :content_type
      t.string :original_filename
      t.binary :content
      t.timestamps
    end
    add_index :binary_columns, [:original_table_id, :original_table_type, :name], :name => :by_owner_field_name # add this line
  end
  def self.down
    drop_table :binary_columns
  end
end

Then apply the schema change,

rake db:migrate

Finally, modify the generated app/models/binary_column.rb to have a polymorphic “belongs_to”

class BinaryColumn < ActiveRecord::Base
  belongs_to :original_table, :polymorphic => true
  def file_extension
    self.original_filename.to_s.split('.').last
  end
end

The usage is simple and straight-forward as-if the columns are in the original table.

m = Member.new
m.name   = "Michael"
m.photo  = IO.read("avatar.png")   #=> binary string
m.resume = File.open("resume.doc") #=> IO object (e.g. when uploading via http form)
m.save!
#=> creates a record in "members" table, saving "Michael" into the "name" column
#=> creates a record in "binary_columns" table, saving "avatar.png" binary into "content" column
#=> creates a record in "binary_columns" table, saving "resume.doc" binary into "content" column

m = Member.last
m.name                            #=> "Michael"
m.photo_attributes                #=> light-weight loading of BinaryColumn object (excludes BLOB)
m.photo_attributes.file_extension #=> "png"
m.photo                           #=> binary content of the "avatar.png" file
m.resume                          #=> binary content of the "resume.doc"

Note: If you MUST have your binary column table called something other than “binary_columns”, just edit ActiveRecord::Extensions::BinaryColumnTable::CLASS_NAME

Note: Population of the “content_type” attribute requires “file” command on OS, i.e. most Unix otherwise, remove “content_type” column from table definition to skip content_type extraction

Note: Accessing the content_type attribute is not sugar coated, add a “_binary_column.content_type” suffix. i.e. from our earlier example

m = Member.last
m.photo                             #=> binary content of the "avatar.png" file
m.photo_binary_column.content_type  #=> "image/png; charset=binary"

You may wish to generate index for that table as well

./script/generate migration AddIndexesToBinaryColumns

Edit the generated db/migrate/*_add_indexes_to_binary_columns.rb to look like this

class AddIndexesToBinaryColumns < ActiveRecord::Migration
  def self.up
    add_index :binary_columns, [:original_table_id, :original_table_type, :name], :name => 'by_original_table_name'
  end

  def self.down
    remove_index :binary_columns, :name => 'by_original_table_name'
  end
end

Then run migration to commit the schema change

rake db:migrate

Copyright © 2009 Chew Choon Keat, released under the MIT license