如何完全删除 Rails 中的模型及其关联？
How to completely remove a model and its associations in Rails?
描述
我在 Ruby 版本 2.6.6 和 Ruby 在 Rails 版本 6.0.3.2.
型号
- 图书
- 作者
协会
一本书属于一位作者。
一位作者 有很多 本书。
目标
删除 Author 模型并将其作为列添加到 Book（字符串类型）。
我做了什么
我创建了 运行 3 个迁移，顺序如下：
AddAuthorToBooks
class AddAuthorToBooks < ActiveRecord::Migration[6.0]
def change
add_column :books, :author, :string
end
end
DropAuthors
class DropAuthors < ActiveRecord::Migration[6.0]
def change
drop_table :authors do |t|
t.string "full_name", null: false
t.timestamps null: false
end
end
end
RemoveAuthorForeignKeyFromBooks
class RemoveAuthorForeignKeyFromBooks < ActiveRecord::Migration[6.0]
def change
remove_foreign_key :books, :authors
end
end
架构
不幸的是，在我 运行 迁移之前我没有架构。 （我尝试检查一个较旧的提交，但模式文件顽固地拒绝更改。）
这是当前版本：
ActiveRecord::Schema.define(version: 2020_08_11_125724) do
create_table "books", force: :cascade do |t|
t.string "title"
t.text "description"
t.string "cover_url"
t.decimal "price"
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.integer "author_id", null: false
t.string "author"
t.index ["author_id"], name: "index_books_on_author_id"
end
create_table "books_genres", id: false, force: :cascade do |t|
t.integer "book_id", null: false
t.integer "genre_id", null: false
t.index ["book_id", "genre_id"], name: "index_books_genres_on_book_id_and_genre_id"
t.index ["genre_id", "book_id"], name: "index_books_genres_on_genre_id_and_book_id"
end
create_table "genres", force: :cascade do |t|
t.string "name"
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
end
create_table "reviews", force: :cascade do |t|
t.string "username"
t.decimal "rating"
t.text "body"
t.integer "book_id", null: false
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.index ["book_id"], name: "index_reviews_on_book_id"
end
add_foreign_key "reviews", "books"
end
问题
作者table被删除了，add_foreign_key "books", "authors"（我想就是这样）也不见了，但是author_id固执地留在了books table.
此外，还有一个整数author_id和一个同名索引。
我在计划什么
我想通过另一次迁移删除这两列，但我不知道那是否会...
- ...解决问题并完全删除旧作者模型，
- ...这是 clean/recommended 做事的方式。如果需要，我可以回滚迁移并尝试更好的方法。
关于异常 `schema.rb` 行为
I tried checking out an older commit, but the schema file stubbornly refuses to change.
这很不寻常。请确认您正在使用 git 跟踪 db/schema.rb 文件。如果它被跟踪，没有理由不检查旧提交 return 到旧状态。届时，您应该能够：
$ rails db:drop
$ rails db:create
$ rails db:schema:load
...将旧模式加载到数据库中。然后，您应该能够 return 使用 git 到最新代码，并且 运行 在创建旧模式的日期之后等待迁移。
关于更简洁的实现方式
在编写以下迁移之前，第一步是删除 Book class 中写入的任何现有关系。例如：
# app/models/book.rb
class Book < ApplicationRecord
# The line below should be deleted! Otherwise, it will probably interfere
# with the `book.update!(author: ...)` line in the migration.
belongs_to :author
end
我已经开始在一个文件中编写相关的迁移，因为它们都是相关的。对我来说，这看起来像：
class MoveAuthorToBooks < ActiveRecord::Migration[6.0]
class Author < ApplicationRecord
end
class Book < ApplicationRecord
end
def up
# Start by adding a string column.
add_column :books, :author, :string
# Let's preserve existing author names.
Book.all.each do |book|
author = Author.find(book.author_id)
book.update!(author: author.name)
end
# Now that the names have been moved to the books table, we don't
# need the relationship to `authors` table anymore. This should
# also delete any related foreign keys - manual foreign key deletion
# should not be required.
remove_column :books, :author_id
# Alternative: If you'd created the `authors_id` column using the
# `add_reference` command, then it's probably best to use the opposite
# `remove_reference` command.
#
#remove_reference :books, :author, index: true, foreign_key: true
# Finally, remove the `authors` table.
drop_table :authors
end
def down
# This can be technically be reversed, but that'll need some more code that
# reverses the action of the `up` function, and it may not be needed.
raise ActiveRecord::IrreversibleMigration
end
end
描述
我在 Ruby 版本 2.6.6 和 Ruby 在 Rails 版本 6.0.3.2.
型号
- 图书
- 作者
协会
一本书属于一位作者。
一位作者 有很多 本书。
目标
删除 Author 模型并将其作为列添加到 Book（字符串类型）。
我做了什么
我创建了 运行 3 个迁移，顺序如下：
AddAuthorToBooks
class AddAuthorToBooks < ActiveRecord::Migration[6.0]
def change
add_column :books, :author, :string
end
end
DropAuthors
class DropAuthors < ActiveRecord::Migration[6.0]
def change
drop_table :authors do |t|
t.string "full_name", null: false
t.timestamps null: false
end
end
end
RemoveAuthorForeignKeyFromBooks
class RemoveAuthorForeignKeyFromBooks < ActiveRecord::Migration[6.0]
def change
remove_foreign_key :books, :authors
end
end
架构
不幸的是，在我 运行 迁移之前我没有架构。 （我尝试检查一个较旧的提交，但模式文件顽固地拒绝更改。）
这是当前版本：
ActiveRecord::Schema.define(version: 2020_08_11_125724) do
create_table "books", force: :cascade do |t|
t.string "title"
t.text "description"
t.string "cover_url"
t.decimal "price"
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.integer "author_id", null: false
t.string "author"
t.index ["author_id"], name: "index_books_on_author_id"
end
create_table "books_genres", id: false, force: :cascade do |t|
t.integer "book_id", null: false
t.integer "genre_id", null: false
t.index ["book_id", "genre_id"], name: "index_books_genres_on_book_id_and_genre_id"
t.index ["genre_id", "book_id"], name: "index_books_genres_on_genre_id_and_book_id"
end
create_table "genres", force: :cascade do |t|
t.string "name"
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
end
create_table "reviews", force: :cascade do |t|
t.string "username"
t.decimal "rating"
t.text "body"
t.integer "book_id", null: false
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.index ["book_id"], name: "index_reviews_on_book_id"
end
add_foreign_key "reviews", "books"
end
问题
作者table被删除了，add_foreign_key "books", "authors"（我想就是这样）也不见了，但是author_id固执地留在了books table.
此外，还有一个整数author_id和一个同名索引。
我在计划什么
我想通过另一次迁移删除这两列，但我不知道那是否会...
- ...解决问题并完全删除旧作者模型，
- ...这是 clean/recommended 做事的方式。如果需要，我可以回滚迁移并尝试更好的方法。
关于异常 `schema.rb` 行为
I tried checking out an older commit, but the schema file stubbornly refuses to change.
这很不寻常。请确认您正在使用 git 跟踪 db/schema.rb 文件。如果它被跟踪，没有理由不检查旧提交 return 到旧状态。届时，您应该能够：
$ rails db:drop
$ rails db:create
$ rails db:schema:load
...将旧模式加载到数据库中。然后，您应该能够 return 使用 git 到最新代码，并且 运行 在创建旧模式的日期之后等待迁移。
关于更简洁的实现方式
在编写以下迁移之前，第一步是删除 Book class 中写入的任何现有关系。例如：
# app/models/book.rb
class Book < ApplicationRecord
# The line below should be deleted! Otherwise, it will probably interfere
# with the `book.update!(author: ...)` line in the migration.
belongs_to :author
end
我已经开始在一个文件中编写相关的迁移，因为它们都是相关的。对我来说，这看起来像：
class MoveAuthorToBooks < ActiveRecord::Migration[6.0]
class Author < ApplicationRecord
end
class Book < ApplicationRecord
end
def up
# Start by adding a string column.
add_column :books, :author, :string
# Let's preserve existing author names.
Book.all.each do |book|
author = Author.find(book.author_id)
book.update!(author: author.name)
end
# Now that the names have been moved to the books table, we don't
# need the relationship to `authors` table anymore. This should
# also delete any related foreign keys - manual foreign key deletion
# should not be required.
remove_column :books, :author_id
# Alternative: If you'd created the `authors_id` column using the
# `add_reference` command, then it's probably best to use the opposite
# `remove_reference` command.
#
#remove_reference :books, :author, index: true, foreign_key: true
# Finally, remove the `authors` table.
drop_table :authors
end
def down
# This can be technically be reversed, but that'll need some more code that
# reverses the action of the `up` function, and it may not be needed.
raise ActiveRecord::IrreversibleMigration
end
end