为什么这个 Rails 迁移会给出'no such table'错误？

Question

在一个新的Rails6项目中，我有一个名为object_classes的表，其中有一列名为ClassList_id。来自schema.rb:

create_table "object_classes", force: :cascade do |t|
t.string "name"
t.integer "ClassList_id", null: false
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.index ["ClassList_id"], name: "index_object_classes_on_ClassList_id"
end

我已经意识到该列应该命名为class_list_id，以符合Rails预期的命名约定。因此，我生成了一个新的迁移：

class FixColumnName < ActiveRecord::Migration[6.0]
def change
rename_column :object_classes, :ClassList_id, :class_list_id
end
end

然而，当我运行此迁移时，我会得到以下错误：

/bin/bash -c "env RBENV_VERSION=2.6.1 /home/asfarley/.rbenv/libexec/rbenv exec bundle exec ruby /home/asfarley/imgseq/bin/spring rails 'db:migrate'"
== 20200716060501 FixColumnName: migrating ====================================
-- rename_column(:object_classes, :ClassList_id, :class_list_id)
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:
SQLite3::SQLException: no such table: main.ClassLists
/home/asfarley/imgseq/db/migrate/20200716060501_fix_column_name.rb:3:in `change'
/home/asfarley/imgseq/bin/rails:9:in `<top (required)>'
/home/asfarley/imgseq/bin/spring:15:in `require'
/home/asfarley/imgseq/bin/spring:15:in `<main>'
Caused by:
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such table: main.ClassLists
/home/asfarley/imgseq/db/migrate/20200716060501_fix_column_name.rb:3:in `change'
/home/asfarley/imgseq/bin/rails:9:in `<top (required)>'
/home/asfarley/imgseq/bin/spring:15:in `require'
/home/asfarley/imgseq/bin/spring:15:in `<main>'
Caused by:
SQLite3::SQLException: no such table: main.ClassLists
/home/asfarley/imgseq/db/migrate/20200716060501_fix_column_name.rb:3:in `change'
/home/asfarley/imgseq/bin/rails:9:in `<top (required)>'
/home/asfarley/imgseq/bin/spring:15:in `require'
/home/asfarley/imgseq/bin/spring:15:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
Process finished with exit code 1

我在这里做错了什么？我正在寻找一个解释，具体解决这里的错误，这样我就可以了解如何在未来避免这种情况。

Answer 1

很难知道故障是Rails还是SQLite，但问题似乎是我为object_classes表定义了一个外键，指向一个不存在的表。通过这次迁移，我能够修复外键约束并重命名列：

class FixColumnName < ActiveRecord::Migration[6.0]
def change
remove_foreign_key :object_classes, :ClassLists
rename_column :object_classes, :ClassList_id, :class_list_id
add_foreign_key :object_classes, :class_lists
end
end

Answer 2

您的语法是正常的，因此错误必须是保留名称错误。可能会尝试删除该列并再次创建该列，请注意迁移时的大写字母，因为它们会使代码不必要地复杂化。试试这个：

rails g migration RemoveClassListIdFromObjectClasses

这将创建一个类似这样的迁移：

def drop 
remove column :object_classes, :class_lis_id
end 

然后运行

rails g migration AddClassListIdToObjectClasses

迁移应该是这样的：

def change
add_column :object_classes, :class_list_id
end

请记住添加数据类型和您可能需要的任何其他内容。在那里，你可以检查它创建的迁移，你可以更改它，也许添加数据类型，也许更改列的大小写，你就可以开始了。

注意：如果有效的话，如果你接受这个答案，我将不胜感激，谢谢！