![Data Integrity Test Suite
MAX_ERRORS = 50
def test_posts_are_valid
errors = []
Post.find_each do |post|
next if post.valid?
errors << [post.id, post.errors.full_messages]
break if errors.size > MAX_ERRORS
end
assert_equal [], errors
end](https://image.slidesharecdn.com/database-150204175643-conversion-gate02/85/Data-Integrity-in-Rails-54-320.jpg)
Data Integrity in Rails
- 1. Data Integrity in Rails Strategies and techniques to make your data bulletproof
- 3. Simple Complex Email ValidationsNot NULL constraint In ApplicationIn Database
- 6. The “NoMethodError” @blog.body.to_html Returns nil undefined method ‘to_html' for nil:NilClass
- 9. Fix in view unless @blog.body.nil? @blog.body.to_html end
- 10. Learnings Likely to encounter the same problem in other places Messy code littered with checks and guards These are all band-aid fixes
- 11. Fix using Rails Validation validates :body, presence: true, if: ->(record) { record.nil? } WTH?!?
- 12. Validations can still be bypassed blog = Blog.new blog.body = nil blog.save(validate: false)
- 13. Learnings Code is unnecessarily hard to read Validations can be bypassed, resulting in incoherent data
- 14. Fix in Database change_column :blog, :body, :text, null: false, default: ''
- 15. Learnings No Code Modification Less Complexity–you never have to deal with both nils and blank strings Work on the assumption that body is never nil
- 17. The “NoMethodError” @post.author.name Returns nil undefined method ‘name' for nil:NilClass Deleting parent but not children results in this error
- 18. Fix in view @post.author.name if @post.author
- 20. Learnings Likely to encounter the same problem in other places Messy code littered with checks and guards These are all band-aid fixes
- 21. Fix using ActiveRecord has_one :author, dependent: :destroy
- 22. Fix using ActiveRecord has_one :author, dependent: :destroy Inefficient if lots of records
- 23. Fix using ActiveRecord has_one :author, dependent: :delete_all Does only one query, but doesn’t run callbacks
- 24. Fix using ActiveRecord has_one :author, dependent: :restrict_with_exception Blows up if you try to delete a parent with children in DB
- 25. Fix using ActiveRecord has_one :author, dependent: :restrict_with_error Shows an error if you try to delete a parent with children in DB
- 26. These strategies can still be bypassed Post.find(1).delete
- 27. Learnings This is better than fixing locally in views But this can still introduce bad data
- 28. Fix in Database add_foreign_key :authors, :posts
- 29. Fix in Database add_foreign_key :authors, :posts Rails 4.2 Feature
- 30. Fix in Database ALTER TABLE `authors` ADD CONSTRAINT `authors_post_id_fk` FOREIGN KEY (`post_id`) REFERENCES `posts`(id);
- 31. Fix in Database add_foreign_key :authors, :posts, on_delete: :cascade Removes all authors when a post is deleted
- 32. Fix in Database add_foreign_key :authors, :posts, on_delete: :restrict :restrict is the default behavior of foreign keys
- 33. Ideal fix has_one :author, dependent: :delete_all add_foreign_key :authors, :posts, on_delete: :restrict
- 34. Learnings The ideal fix never allows someone to directly introduce orphan data, but still does the optimized cascading behavior when deleted in ActiveRecord.
- 35. Duplicate Data
- 36. Uniqueness Validation validates :name, uniqueness: true Author.where(name: "Mr. Duplicate").count # => 2
- 37. Uniqueness Validation author = Author.new author.name = "Mr. Duplicate" author.save(validate: false)
- 38. Unique Index add_index :authors, :name, unique: true
- 39. Unique Index PG::Error: ERROR: could not create unique index "index_authors_on_name" DETAIL: Key (name)=(Mr. Duplicate) is duplicated.
- 40. Ways of Removing Duplicate Data Use SQL to arbitrarily remove duplicates Use scripts to automatically merge content in rows Manually merge content/remove duplicate rows
- 41. Unique Index Protects Data from having Duplicates PG::Error: ERROR: duplicate key value violates unique constraint "index_authors_on_name" DETAIL: Key (title)=(Mr. Duplicate) already exists This error is thrown every time the Active Record validation is bypassed
- 42. Unique Index Protects Data from having Duplicates def save_with_retry_on_unique(*args) retry_on_exception(ActiveRecord::RecordNotUnique) do save(*args) end end Retries saving when error is thrown, so the validation can take over
- 43. Unique Index Protects Data from having Duplicates def save_with_retry_on_unique(*args) retry_on_exception(ActiveRecord::RecordNotUnique) do save(*args) end end Retries only once Calls the block only once
- 44. One-to-One Relationships add_index :authors, :name, unique: true Protects from associating multiple records to the parent
- 45. Learnings Active Record validations are not meant for data integrity. Incoherent Data can still be introduced. Database level index on unique makes sure data is never duplicated. Rails will skip validations a lot in concurrent situations, so always handle the underlying ActiveRecord::RecordNotUnique Error. Don’t forget to add unique index on one-to-one relationships.
- 47. Polymorphic Association class Post has_many :comments, as: :commentable end class Comment belongs_to :commentable, polymorphic: true end Both commentable_type and commentable_id are stored in the database.
- 48. Polymorphic Association class Post has_many :comments, as: :commentable end class Comment belongs_to :commentable, polymorphic: true end There is no way to add foreign keys to polymorphic associations.
- 49. Learnings There is no SQL standard way of adding polymorphic associations. Referential Integrity is compromised when we use this ActiveRecord pattern. Expensive to index. The data distribution isn’t usually uniform. Harder to JOIN in SQL.
- 50. Database-friendly Polymorphic Associations class Post has_many :comments, class_name: 'PostComment' end class PostComment include Commentable belongs_to :post end
- 51. Learnings Adding one table for each child type maintains data integrity. Foreign keys can be added. Extract similar behaviors using modules in Ruby in the application. Create a non-table backed Ruby class for creating comments Use class_name option to designate which class name to use when retrieving records.
- 52. Learnings Easier to grok and operate. Harder to aggregate over all comments regardless of type. More expensive to add another parent type. Use specific tables if you care for data integrity. If data integrity is a non-issue, use polymorphic associations. Event logging or activity feeds are good examples.
- 54. Data Integrity Test Suite MAX_ERRORS = 50 def test_posts_are_valid errors = [] Post.find_each do |post| next if post.valid? errors << [post.id, post.errors.full_messages] break if errors.size > MAX_ERRORS end assert_equal [], errors end
- 55. Data Integrity Test Suite def test_post_bodys_are_not_nil assert_equal 0, Post.where(body: nil).count end
- 56. Learnings Proactive techniques work best They’re not always feasible if you have bad data already Reactive integrity checks are a good alternative Run these regularly against production data to surface errors up. Avoid using complex constraints.
- 57. Recap Not null constraints Unique indexes Foreign keys Refactor Polymorphic association into separate tables Reactive integrity checks