mirror of
https://github.com/rails/rails.git
synced 2022-11-09 12:12:34 -05:00
de6b4efa3e
In a multiple database application, associations can't join across databases. When set, this option tells Rails to make 2 or more queries rather than using joins for associations. Set the option on a has many through association: ```ruby class Dog has_many :treats, through: :humans, disable_joins: true has_many :humans end ``` Then instead of generating join SQL, two queries are used for `@dog.treats`: ``` SELECT "humans"."id" FROM "humans" WHERE "humans"."dog_id" = ? [["dog_id", 1]] SELECT "treats".* FROM "treats" WHERE "treats"."human_id" IN (?, ?, ?) [["human_id", 1], ["human_id", 2], ["human_id", 3]] ``` This code is extracted from a gem we use internally at GitHub which means the implementation here is used in production daily and isn't experimental. I often get the question "why can't Rails do this automatically" so I figured I'd include the answer in the commit. Rails can't do this automatically because associations are lazily loaded. `dog.treats` needs to load `Dog`, then `Human` and then `Treats`. When `dog.treats` is called Rails pre-generates the SQL that will be run and puts that information into a reflection object. Because the SQL parts are pre-generated, as soon as `dog.treats` is loaded it's too late to skip a join. The join is already available on the object and that join is what's run to load `treats` from `dog` through `humans`. I think the only way to avoid setting an option on the association is to rewrite how and when the SQL is generated for associations which is a large undertaking. Basically the way that Active Record associations are designed, it is currently impossible to have Rails figure out to not join (loading the association will cause the join to occur, and that join will raise an error if the models don't live in the same db). The original implementation was written by me and Aaron. Lee helped port over tests, and I refactored the extraction to better match Rails style. Co-authored-by: Lee Quarella <leequarella@gmail.com> Co-authored-by: Aaron Patterson <aaron@rubyonrails.org>
304 lines
14 KiB
Ruby
304 lines
14 KiB
Ruby
# frozen_string_literal: true
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class Author < ActiveRecord::Base
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has_many :posts
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has_many :serialized_posts
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has_one :post
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has_many :very_special_comments, through: :posts
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has_many :posts_with_comments, -> { includes(:comments) }, class_name: "Post"
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has_many :popular_grouped_posts, -> { includes(:comments).group("type").having("SUM(legacy_comments_count) > 1").select("type") }, class_name: "Post"
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has_many :posts_with_comments_sorted_by_comment_id, -> { includes(:comments).order("comments.id") }, class_name: "Post"
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has_many :posts_sorted_by_id, -> { order(:id) }, class_name: "Post"
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has_many :posts_sorted_by_id_limited, -> { order("posts.id").limit(1) }, class_name: "Post"
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has_many :posts_with_categories, -> { includes(:categories) }, class_name: "Post"
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has_many :posts_with_comments_and_categories, -> { includes(:comments, :categories).order("posts.id") }, class_name: "Post"
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has_many :posts_with_special_categorizations, class_name: "PostWithSpecialCategorization"
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has_one :post_about_thinking, -> { where("posts.title like '%thinking%'") }, class_name: "Post"
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has_one :post_about_thinking_with_last_comment, -> { where("posts.title like '%thinking%'").includes(:last_comment) }, class_name: "Post"
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has_many :comments, through: :posts do
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def ratings
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Rating.joins(:comment).merge(self)
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end
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end
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has_many :comments_with_order, -> { ordered_by_post_id }, through: :posts, source: :comments
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has_many :no_joins_comments, through: :posts, disable_joins: :true, source: :comments
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has_many :comments_with_foreign_key, through: :posts, source: :comments, foreign_key: :post_id
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has_many :no_joins_comments_with_foreign_key, through: :posts, disable_joins: :true, source: :comments, foreign_key: :post_id
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has_many :members,
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through: :comments_with_order,
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source: :origin,
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source_type: "Member"
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has_many :no_joins_members,
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through: :comments_with_order,
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source: :origin,
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source_type: "Member",
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disable_joins: true
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has_many :ordered_members,
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-> { order(id: :desc) },
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through: :comments_with_order,
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source: :origin,
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source_type: "Member"
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has_many :no_joins_ordered_members,
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-> { order(id: :desc) },
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through: :comments_with_order,
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source: :origin,
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source_type: "Member",
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disable_joins: true
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has_many :ratings, through: :comments
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has_many :good_ratings,
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-> { where("ratings.value > 5") },
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through: :comments,
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source: :ratings
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has_many :no_joins_ratings, through: :no_joins_comments, disable_joins: :true, source: :ratings
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has_many :no_joins_good_ratings,
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-> { where("ratings.value > 5") },
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through: :comments,
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source: :ratings,
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disable_joins: true
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has_many :comments_containing_the_letter_e, through: :posts, source: :comments
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has_many :comments_with_order_and_conditions, -> { order("comments.body").where("comments.body like 'Thank%'") }, through: :posts, source: :comments
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has_many :comments_with_include, -> { includes(:post).where(posts: { type: "Post" }) }, through: :posts, source: :comments
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has_many :comments_for_first_author, -> { for_first_author }, through: :posts, source: :comments
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has_many :first_posts
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has_many :comments_on_first_posts, -> { order("posts.id desc, comments.id asc") }, through: :first_posts, source: :comments
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has_one :first_post
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has_one :comment_on_first_post, -> { order("posts.id desc, comments.id asc") }, through: :first_post, source: :comments
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has_many :thinking_posts, -> { where(title: "So I was thinking") }, dependent: :delete_all, class_name: "Post"
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has_many :welcome_posts, -> { where(title: "Welcome to the weblog") }, class_name: "Post"
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has_many :welcome_posts_with_one_comment,
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-> { where(title: "Welcome to the weblog").where(comments_count: 1) },
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class_name: "Post"
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has_many :welcome_posts_with_comments,
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-> { where(title: "Welcome to the weblog").where("legacy_comments_count > 0") },
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class_name: "Post"
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has_many :comments_desc, -> { order("comments.id DESC") }, through: :posts_sorted_by_id, source: :comments
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has_many :unordered_comments, -> { unscope(:order).distinct }, through: :posts_sorted_by_id_limited, source: :comments
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has_many :funky_comments, through: :posts, source: :comments
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has_many :ordered_uniq_comments, -> { distinct.order("comments.id") }, through: :posts, source: :comments
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has_many :ordered_uniq_comments_desc, -> { distinct.order("comments.id DESC") }, through: :posts, source: :comments
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has_many :readonly_comments, -> { readonly }, through: :posts, source: :comments
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has_many :special_posts
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has_many :special_post_comments, through: :special_posts, source: :comments
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has_many :special_posts_with_default_scope, class_name: "SpecialPostWithDefaultScope"
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has_many :sti_posts, class_name: "StiPost"
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has_many :sti_post_comments, through: :sti_posts, source: :comments
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has_many :special_nonexistent_posts, -> { where("posts.body = 'nonexistent'") }, class_name: "SpecialPost"
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has_many :special_nonexistent_post_comments, -> { where("comments.post_id" => 0) }, through: :special_nonexistent_posts, source: :comments
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has_many :nonexistent_comments, through: :posts
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has_many :hello_posts, -> { where "posts.body = 'hello'" }, class_name: "Post"
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has_many :hello_post_comments, through: :hello_posts, source: :comments
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has_many :posts_with_no_comments, -> { where("comments.id" => nil).includes(:comments) }, class_name: "Post"
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has_many :posts_with_no_comments_2, -> { left_joins(:comments).where("comments.id": nil) }, class_name: "Post"
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has_many :hello_posts_with_hash_conditions, -> { where(body: "hello") }, class_name: "Post"
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has_many :hello_post_comments_with_hash_conditions, through: :hello_posts_with_hash_conditions, source: :comments
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has_many :other_posts, class_name: "Post"
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has_many :posts_with_callbacks, class_name: "Post", before_add: :log_before_adding,
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after_add: :log_after_adding,
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before_remove: :log_before_removing,
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after_remove: :log_after_removing
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has_many :posts_with_thrown_callbacks, class_name: "Post", before_add: :throw_abort,
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after_add: :ensure_not_called,
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before_remove: :throw_abort,
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after_remove: :ensure_not_called
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has_many :posts_with_proc_callbacks, class_name: "Post",
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before_add: Proc.new { |o, r| o.post_log << "before_adding#{r.id || '<new>'}" },
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after_add: Proc.new { |o, r| o.post_log << "after_adding#{r.id || '<new>'}" },
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before_remove: Proc.new { |o, r| o.post_log << "before_removing#{r.id}" },
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after_remove: Proc.new { |o, r| o.post_log << "after_removing#{r.id}" }
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has_many :posts_with_multiple_callbacks, class_name: "Post",
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before_add: [:log_before_adding, Proc.new { |o, r| o.post_log << "before_adding_proc#{r.id || '<new>'}" }],
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after_add: [:log_after_adding, Proc.new { |o, r| o.post_log << "after_adding_proc#{r.id || '<new>'}" }]
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has_many :unchangeable_posts, class_name: "Post", before_add: :raise_exception, after_add: :log_after_adding
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has_many :categorizations, -> { }
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has_many :categories, through: :categorizations
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has_many :named_categories, through: :categorizations
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has_many :special_categorizations
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has_many :special_categories, through: :special_categorizations, source: :category
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has_one :special_category, through: :special_categorizations, source: :category
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has_many :general_categorizations, -> { joins(:category).where("categories.name": "General") }, class_name: "Categorization"
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has_many :general_posts, through: :general_categorizations, source: :post
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has_many :special_categories_with_conditions, -> { where(categorizations: { special: true }) }, through: :categorizations, source: :category
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has_many :nonspecial_categories_with_conditions, -> { where(categorizations: { special: false }) }, through: :categorizations, source: :category
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has_many :categories_like_general, -> { where(name: "General") }, through: :categorizations, source: :category, class_name: "Category"
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has_many :categorized_posts, through: :categorizations, source: :post
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has_many :unique_categorized_posts, -> { distinct }, through: :categorizations, source: :post
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has_many :nothings, through: :kateggorisatons, class_name: "Category"
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has_many :author_favorites
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has_many :favorite_authors, -> { order("name") }, through: :author_favorites
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has_many :taggings, through: :posts, source: :taggings
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has_many :taggings_2, through: :posts, source: :tagging
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has_many :tags, through: :posts
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has_many :ordered_tags, through: :posts
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has_many :post_categories, through: :posts, source: :categories
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has_many :tagging_tags, through: :taggings, source: :tag
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has_many :similar_posts, -> { distinct }, through: :tags, source: :tagged_posts
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has_many :ordered_posts, -> { distinct }, through: :ordered_tags, source: :tagged_posts
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has_many :distinct_tags, -> { select("DISTINCT tags.*").order("tags.name") }, through: :posts, source: :tags
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has_many :tags_with_primary_key, through: :posts
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has_many :books
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has_many :published_books, class_name: "PublishedBook"
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has_many :unpublished_books, -> { where(status: [:proposed, :written]) }, class_name: "Book"
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has_many :subscriptions, through: :books
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has_many :subscribers, -> { order("subscribers.nick") }, through: :subscriptions
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has_many :distinct_subscribers, -> { select("DISTINCT subscribers.*").order("subscribers.nick") }, through: :subscriptions, source: :subscriber
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has_one :essay, primary_key: :name, as: :writer
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has_one :essay_category, through: :essay, source: :category
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has_one :essay_owner, through: :essay, source: :owner
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has_one :essay_2, primary_key: :name, class_name: "Essay", foreign_key: :author_id
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has_one :essay_category_2, through: :essay_2, source: :category
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has_many :essays, primary_key: :name, as: :writer
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has_many :essay_categories, through: :essays, source: :category
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has_many :essay_owners, through: :essays, source: :owner
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has_many :essays_2, primary_key: :name, class_name: "Essay", foreign_key: :author_id
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has_many :essay_categories_2, through: :essays_2, source: :category
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belongs_to :owned_essay, primary_key: :name, class_name: "Essay"
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has_one :owned_essay_category, through: :owned_essay, source: :category
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belongs_to :author_address, dependent: :destroy
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belongs_to :author_address_extra, dependent: :delete, class_name: "AuthorAddress"
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has_many :category_post_comments, through: :categories, source: :post_comments
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has_many :misc_posts, -> { where(posts: { title: ["misc post by bob", "misc post by mary"] }) }, class_name: "Post"
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has_many :misc_post_first_blue_tags, through: :misc_posts, source: :first_blue_tags
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has_many :misc_post_first_blue_tags_2, -> { where(posts: { title: ["misc post by bob", "misc post by mary"] }) },
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through: :posts, source: :first_blue_tags_2
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has_many :posts_with_default_include, class_name: "PostWithDefaultInclude"
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has_many :comments_on_posts_with_default_include, through: :posts_with_default_include, source: :comments
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has_many :posts_with_signature, ->(record) { where("posts.title LIKE ?", "%by #{record.name.downcase}%") }, class_name: "Post"
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has_many :posts_mentioning_author, ->(record = nil) { where("posts.body LIKE ?", "%#{record&.name&.downcase}%") }, class_name: "Post"
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has_one :recent_post, -> { order(id: :desc) }, class_name: "Post"
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has_one :recent_response, through: :recent_post, source: :comments
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has_many :posts_with_extension, -> { order(:title) }, class_name: "Post" do
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def extension_method; end
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end
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has_many :posts_with_extension_and_instance, ->(record) { order(:title) }, class_name: "Post" do
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def extension_method; end
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end
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has_many :top_posts, -> { order(id: :asc) }, class_name: "Post"
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has_many :other_top_posts, -> { order(id: :asc) }, class_name: "Post"
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has_many :topics, primary_key: "name", foreign_key: "author_name"
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has_many :topics_without_type, -> { select(:id, :title, :author_name) },
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class_name: "Topic", primary_key: "name", foreign_key: "author_name"
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has_many :lazy_readers_skimmers_or_not, through: :posts
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has_many :lazy_readers_skimmers_or_not_2, through: :posts_with_no_comments, source: :lazy_readers_skimmers_or_not
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has_many :lazy_readers_skimmers_or_not_3, through: :posts_with_no_comments_2, source: :lazy_readers_skimmers_or_not
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attr_accessor :post_log
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after_initialize :set_post_log
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def set_post_log
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@post_log = []
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end
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def label
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"#{id}-#{name}"
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end
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def social
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%w(twitter github)
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end
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validates_presence_of :name
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private
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def throw_abort(_)
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throw(:abort)
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end
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def ensure_not_called(_)
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raise
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end
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def log_before_adding(object)
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@post_log << "before_adding#{object.id || '<new>'}"
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end
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def log_after_adding(object)
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@post_log << "after_adding#{object.id}"
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end
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def log_before_removing(object)
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@post_log << "before_removing#{object.id}"
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end
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def log_after_removing(object)
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@post_log << "after_removing#{object.id}"
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end
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def raise_exception(object)
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raise Exception.new("You can't add a post")
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end
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end
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class AuthorAddress < ActiveRecord::Base
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has_one :author
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def self.destroyed_author_address_ids
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@destroyed_author_address_ids ||= []
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end
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before_destroy do |author_address|
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AuthorAddress.destroyed_author_address_ids << author_address.id
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end
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end
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class AuthorFavorite < ActiveRecord::Base
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belongs_to :author
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belongs_to :favorite_author, class_name: "Author"
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end
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class AuthorFavoriteWithScope < ActiveRecord::Base
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self.table_name = "author_favorites"
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default_scope { order(id: :asc) }
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belongs_to :author
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belongs_to :favorite_author, class_name: "Author"
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end
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