添加:default =>在现有的Rails列中为boolean为true [英] Adding :default => true to boolean in existing Rails column

问题描述

我看到了一些问题(即 )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.

我尝试过:

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

哪个返回-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:show_attribute的值仍为nil.在上面我提到的问题中，它说在PostgreSQL中您需要手动更新.由于我使用的是PostgreSQL，因此在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

有人可以告诉我我在做什么错吗?

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

推荐答案

change_column是ActiveRecord::Migration的一种方法，因此您不能在控制台中这样调用它.

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，请创建一个新的迁移:

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

rails g migration add_default_value_to_show_attribute

然后在迁移中创建:

# 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

或更具体的选择:

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 task或只是进入rails console并更新所有记录.

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.

将t.boolean :show_attribute, :default => true添加到create_profiles迁移中时，如果不执行任何操作是正常的.仅执行尚未运行的迁移.如果您从一个全新的数据库开始，那么它将默认设置为true.

When you added t.boolean :show_attribute, :default => true to the create_profiles migration, it's normal if 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.

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