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https://github.com/rtomayko/replicate

Dump and load relational objects between Ruby environments.
https://github.com/rtomayko/replicate

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Dump and load relational objects between Ruby environments.

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README 

        
Dump and load relational objects between Ruby environments.

===========================================================



*This repository is archived and no longer actively maintained by @rtomayko as of 2017-11-08. Issues and PRs documenting current issues have been intentionally left open for informational purposes.*



The project started at GitHub to simplify the process of getting real production

data into development and staging environments. We use it to replicate entire

repository data (including associated issue, pull request, commit comment, etc.

records) from production to our development environments with a single command.

It's excessively useful for troubleshooting issues, support requests, and

exception reports as well as for establishing real data for evaluating design

concepts.



Synopsis

--------



### Installing



    $ gem install replicate



### Dumping objects



Evaluate a Ruby expression, dumping all resulting objects to standard output:



    $ replicate -r ./config/environment -d "User.find(1)" > user.dump

    ==> dumped 4 total objects:

    Profile        1

    User           1

    UserEmail      2



The `-r ./config/environment` option is used to require environment setup and

model instantiation code needed by the ruby expression.



### Dumping many objects with a dump script



Dump scripts are normal ruby source files evaluated in the context of the

dumper. The `dump(object)` method is used to put objects into the dump stream.



```ruby

# config/replicate/dump-stuff.rb

require 'config/environment'



%w[rtomayko/tilt rtomayko/bcat].each do |repo_name|

  repo = Repository.find_by_name_with_owner(repo_name)

  dump repo

  dump repo.commit_comments

  dump repo.issues

end

```



Run the dump script:



    $ replicate -d config/replicate/dump-stuff.rb > repos.dump

    ==> dumped 1479 total objects:

    AR::Habtm                   101

    CommitComment                95

    Issue                       101

    IssueComment                427

    IssueEvent                  308

    Label                         5

    Language                     19

    LanguageName                  1

    Milestone                     3

    Organization                  4

    Profile                      82

    PullRequest                  44

    PullRequestReviewComment      8

    Repository                   20

    Team                          4

    TeamMember                    6

    User                         89

    UserEmail                   162



### Loading many objects:



    $ replicate -r ./config/environment -l < repos.dump

    ==> loaded 1479 total objects:

    AR::Habtm                   101

    CommitComment                95

    Issue                       101

    IssueComment                427

    IssueEvent                  308

    Label                         5

    Language                     19

    LanguageName                  1

    Milestone                     3

    Organization                  4

    Profile                      82

    PullRequest                  44

    PullRequestReviewComment      8

    Repository                   20

    Team                          4

    TeamMember                    6

    User                         89

    UserEmail                   162



### Dumping and loading over ssh



    $ remote_command="replicate -r /app/config/environment -d 'User.find(1234)'"

    $ ssh example.org "$remote_command" |replicate -r ./config/environment -l



ActiveRecord

------------



Basic support for dumping and loading ActiveRecord objects is included. The

tests pass under ActiveRecord versions 2.2.3, 2.3.5, 2.3.14, 3.0.10, 3.1.0, and 3.2.0 under

MRI 1.8.7 as well as under MRI 1.9.2.



To use customization macros in your models, require the replicate library after

ActiveRecord (in e.g., `config/initializers/libraries.rb`):



```ruby

require 'active_record'

require 'replicate'

```



ActiveRecord support works sensibly without customization so this isn't strictly

necessary to use the `replicate` command. The following sections document the

available customization macros.



### Association Dumping



The baked in support adds some more or less sensible default behavior for all

subclasses of `ActiveRecord::Base` such that dumping an object will bring in

objects related via `belongs_to` and `has_one` associations.



Unlike 1:1 associations, `has_many` and `has_and_belongs_to_many` associations

are not automatically included. Doing so would quickly lead to the entire

database being sucked in. It can be useful to mark specific associations for

automatic inclusion using the `replicate_associations` macro. For instance,

to always include `EmailAddress` records belonging to a `User`:



```ruby

class User < ActiveRecord::Base

  belongs_to :profile

  has_many   :email_addresses



  replicate_associations :email_addresses

end

```



You may also do this by passing an option in your dump script:



```ruby

dump User.all, :associations => [:email_addresses]

```



### Natural Keys



By default, the loader attempts to create a new record with a new primary key id

for all objects. This can lead to unique constraint errors when a record already

exists with matching attributes. To update existing records instead of

creating new ones, define a natural key for the model using the `replicate_natural_key`

macro:



```ruby

class User < ActiveRecord::Base

  belongs_to :profile

  has_many   :email_addresses



  replicate_natural_key :login

  replicate_associations :email_addresses

end



class EmailAddress < ActiveRecord::Base

  belongs_to :user

  replicate_natural_key :user_id, :email

end

```



Multiple attribute names may be specified to define a compound key. Foreign key

column attributes (`user_id`) are often included in natural keys.



### Omission of attributes and associations



You might want to exclude some attributes or associations from being dumped. For

this, use the replicate_omit_attributes macro:



```ruby

class User < ActiveRecord::Base

  has_one    :profile



  replicate_omit_attributes :created_at, :profile

end

```



You can omit belongs_to associations by omitting the foreign key column.



You may also do this by passing an option in your dump script:



```ruby

dump User.all, :omit => [:profile]

```



### Validations and Callbacks



__IMPORTANT:__ All ActiveRecord validations and callbacks are disabled on the

loading side. While replicate piggybacks on AR for relationship information and

uses `ActiveRecord::Base#save` to write objects to the database, it's designed

to act as a simple dump / load tool.



It's sometimes useful to run certain types of callbacks on replicate. For

instance, you might want to create files on disk or load information into a

separate data store any time an object enters the database. The best way to go

about this currently is to override the model's `load_replicant` class method:



```ruby

class User < ActiveRecord::Base

  def self.load_replicant(type, id, attrs)

    id, object = super

    object.register_in_redis

    object.some_other_callback

    [id, object]

  end

end

```



This interface will be improved in future versions.



Custom Objects

--------------



Other object types may be included in the dump stream so long as they implement

the `dump_replicant` and `load_replicant` methods.



### dump_replicant



The dump side calls `#dump_replicant(dumper, opts={})` on each object. The method must

call `dumper.write()` with the class name, id, and hash of primitively typed

attributes for the object:



```ruby

class User

  attr_reader   :id

  attr_accessor :name, :email



  def dump_replicant(dumper, opts={})

    attributes = { 'name' => name, 'email' => email }

    dumper.write self.class, id, attributes, self

  end

end

```



### load_replicant



The load side calls `::load_replicant(type, id, attributes)` on the class to

load each object into the current environment. The method must return an

`[id, object]` tuple:



```ruby

class User

  def self.load_replicant(type, id, attributes)

    user = User.new

    user.name  = attributes['name']

    user.email = attributes['email']

    user.save!

    [user.id, user]

  end

end

```



How it works

------------



The dump format is designed for streaming relational data. Each object is

encoded as a `[type, id, attributes]` tuple and marshalled directly onto the

stream. The `type` (class name string) and `id` must form a distinct key when

combined, `attributes` must consist of only string keys and simply typed values.



Relationships between objects in the stream are managed as follows:



 - An object's attributes may encode references to objects that precede it

   in the stream using a simple tuple format: `[:id, 'User', 1234]`.



 - The dump side ensures that objects are written to the dump stream in

   "reference order" such that when an object A includes a reference attribute

   to an object B, B is guaranteed to arrive before A.



 - The load side maintains a mapping of ids from the dumping system to the newly

   replicated objects on the loading system. When the loader encounters a

   reference value `[:id, 'User', 1234]` in an object's attributes, it converts it

   to the load side id value.



Dumping and loading happens in a streaming fashion. There is no limit on the

number of objects included in the stream.