Ruby on rails Rails迁移-Mysql2:：错误：指定的键太长；最大密钥长度为767字节

我正在从事RubyonRails项目

我使用MySQL2作为适配器

这是一个迁移文件

class CreatePages < ActiveRecord::Migration[6.0]
  def change
    create_table :pages do |t|
      t.string :base_url, null: false
      t.string :html, null: false
      t.string :styles, null: false
      t.text :images, null: false

      t.timestamps
    end

    add_index :pages, [:base_url, :html, :styles, :images], length: { images: 767 }, unique: true
  end
end

我得到了这个错误

Mysql2::Error: Specified key was too long; max key length is 767 bytes
/home/ubuntu/project/db/migrate/20200504001308_create_pages.rb:12:in `change'

Caused by:
ActiveRecord::StatementInvalid: Mysql2::Error: Specified key was too long; max key length is 767 bytes
/home/ubuntu/project/db/migrate/20200504001308_create_pages.rb:12:in `change'

Caused by:
Mysql2::Error: Specified key was too long; max key length is 767 bytes
/home/ubuntu/project/db/migrate/20200504001308_create_pages.rb:12:in `change'

---

有人能帮我吗？

根据您的表编码，某些字符集每个字符可以使用多个字节。MySQL中的

utf8

编码要求每个字符有3个字节，因此此编码的字符串限制应为255（767/3）。如果编码为utf8mb4（每个字符需要4个字节），则限制应设置为191（767/4）

因此，您的迁移文件可能如下所示：

class CreatePages

这似乎是旧版本MySQL的一个限制，这就是Rails默认情况下的原因

Mysql2::Error: Specified key was too long; max key length is 767 bytes
/home/ubuntu/project/db/migrate/20200504001308_create_pages.rb:12:in `change'

Caused by:
ActiveRecord::StatementInvalid: Mysql2::Error: Specified key was too long; max key length is 767 bytes
/home/ubuntu/project/db/migrate/20200504001308_create_pages.rb:12:in `change'

Caused by:
Mysql2::Error: Specified key was too long; max key length is 767 bytes
/home/ubuntu/project/db/migrate/20200504001308_create_pages.rb:12:in `change'