添加:默认 =>true 为现有 Rails 列中的布尔值

问题描述：

我看到了一些问题(即这个)在这里关于向现有列添加默认布尔值.所以我尝试了 change_column 建议，但我一定做得不对.

I've seen a few questions (namely this one) here on SO about adding a default boolean value to an existing column. So I tried the change_column suggestion but I mustn't be doing it right.

我试过了:

$ change_column :profiles, :show_attribute, :boolean, :default => true

返回-bash:change_column: command not found

然后我跑了:

$ rails g change_column :profiles, :show_attribute, :boolean, :default => true

...和

$ rails change_column :profiles, :show_attribute, :boolean, :default => true

然后运行rake db:migrate，但是:show_attribute 的值仍然是nil.在我上面引用的问题中，它说在 PostgreSQL 中您需要手动更新它.由于我使用的是 PostgreSQL，因此我在 create_profiles 迁移中添加了以下内容:

Then ran rake db:migrate, but the value for :show_attribute remained nil. In the question I referenced above it says in PostgreSQL you need to update it manually. Since I'm using PostgreSQL I added the following in my create_profiles migration:

t.boolean :show_attribute, :default => true

谁能告诉我我在这里做错了什么?

Can someone tell me what I'm doing wrong here?

答

change_column 是 ActiveRecord::Migration 的一个方法，所以不能这样调用在控制台中.

change_column is a method of ActiveRecord::Migration, so you can't call it like that in the console.

如果要为此列添加默认值，请创建新迁移:

If you want to add a default value for this column, create a new migration:

rails g 迁移 add_default_value_to_show_attribute

然后在创建的迁移中:

# That's the more generic way to change a column
def up
  change_column :profiles, :show_attribute, :boolean, default: true
end

def down
  change_column :profiles, :show_attribute, :boolean, default: nil
end

或更具体的选项:

def up
    change_column_default :profiles, :show_attribute, true
end

def down
    change_column_default :profiles, :show_attribute, nil
end

然后运行rake db:migrate.

它不会对已创建的记录进行任何更改.为此，您必须创建一个 rake 任务 或直接进入 rails 控制台 并更新所有记录(我不建议在生产中这样做).

It won't change anything to the already created records. To do that you would have to create a rake task or just go in the rails console and update all the records (which I would not recommend in production).

当你添加 t.boolean :show_attribute, :default =>对于 create_profiles 迁移来说是真的，预计它什么也没做.仅执行尚未运行的迁移.如果您从一个全新的数据库开始，那么它会将默认值设置为 true.

When you added t.boolean :show_attribute, :default => true to the create_profiles migration, it's expected that it didn't do anything. Only migrations that have not already been ran are executed. If you started with a fresh database, then it would set the default to true.

添加:默认 =>true 为现有 Rails 列中的布尔值

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