Seed Dump is a Rails 4 and 5 plugin that adds a rake task named db:seed:dump.

It allows you to create seed data files from the existing data in your database.

You can also use Seed Dump from the Rails console. See below for usage examples.

Note: if you want to use Seed Dump with Rails 3 or earlier, use version 0.5.3.

Add it to your Gemfile with:

gem 'seed_dump'

Or install it by hand:

$ gem install seed_dump

Dump all data directly to db/seeds.rb:

  $ rake db:seed:dump

Result:

Product.create!([
  { category_id: 1, description: "Long Sleeve Shirt", name: "Long Sleeve Shirt" },
  { category_id: 3, description: "Plain White Tee Shirt", name: "Plain T-Shirt" }
])
User.create!([
  { password: "123456", username: "test_1" },
  { password: "234567", username: "test_2" }
])

Dump only data from the users table and dump a maximum of 1 record:

$ rake db:seed:dump MODELS=User LIMIT=1

Result:

User.create!([
  { password: "123456", username: "test_1" }
])

Append to db/seeds.rb instead of overwriting it:

rake db:seed:dump APPEND=true

Use another output file instead of db/seeds.rb:

rake db:seed:dump FILE=db/seeds/users.rb

Exclude name and age from the dump:

rake db:seed:dump EXCLUDE=name,age

There are more options that can be set— see below for all of them.

Output a dump of all User records:

irb(main):001:0> puts SeedDump.dump(User)
User.create!([
  { password: "123456", username: "test_1" },
  { password: "234567", username: "test_2" }
])

Write the dump to a file:

irb(main):002:0> SeedDump.dump(User, file: 'db/seeds.rb')

Append the dump to a file:

irb(main):003:0> SeedDump.dump(User, file: 'db/seeds.rb', append: true)

Exclude name and age from the dump:

irb(main):004:0> SeedDump.dump(User, exclude: [:name, :age])

Options are specified as a Hash for the second argument.

In the console, any relation of ActiveRecord rows can be dumped (not individual objects though)

irb(main):001:0> puts SeedDump.dump(User.where(is_admin: false))
User.create!([
  { password: "123456", username: "test_1", is_admin: false },
  { password: "234567", username: "test_2", is_admin: false }
])

Options are common to both the Rake task and the console, except where noted.

append: If set to true, append the data to the file instead of overwriting it. Default: false.

batch_size: Controls the number of records that are written to file at a given time. Default: 1000. If you're running out of memory when dumping, try decreasing this. If things are dumping too slow, trying increasing this.

exclude: Attributes to be excluded from the dump. Pass a comma-separated list to the Rake task (i.e. name,age) and an array on the console (i.e. [:name, :age]). Default: [:id, :created_at, :updated_at].

file: Write to the specified output file. The Rake task default is db/seeds.rb. The console returns the dump as a string by default.

import: If true, output will be in the format needed by the activerecord-import gem, rather than the default format. Default: false.

limit: Dump no more than this amount of data. Default: no limit. Rake task only. In the console just pass in an ActiveRecord::Relation with the appropriate limit (e.g. SeedDump.dump(User.limit(5))).

conditions: Dump only specific records. In the console just pass in an ActiveRecord::Relation with the appropriate conditions (e.g. SeedDump.dump(User.where(state: :active))).

model[s]: Restrict the dump to the specified comma-separated list of models. Default: all models. If you are using a Rails engine you can dump a specific model by passing "EngineName::ModelName". Rake task only. Example: rake db:seed:dump MODELS="User, Position, Function"

models_exclude: Exclude the specified comma-separated list of models from the dump. Default: no models excluded. Rake task only. Example: rake db:seed:dump MODELS_EXCLUDE="User"