更新一列，所有行

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最佳答案

Try this:

Foo.update_all(some_column: "bar")

This will generate SQL query to database:

UPDATE "foos" SET "some_column" = "bar";

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Since you already created the new field in a previous migration, create a brand new migration:

rails g migration UpdateFoos

Modify the migration:

def self.up
say_with_time "Updating foos..." do
Foo.find(:all).each do |f|
f.update_attribute :myattribute, 'value'
end
end
end


# from command line
Rake db:migrate

Let me know if this works, it might need a few adjustments. See rails docs for more:

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you can do like this:

Foo.update_all(new_column: "bar")

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Of course you can use smth like Foo.update_all(:myattribute => "value"), but it'll modify only already created data. To set default value for all "future" data it's a good way to create a separate migration like this:

rails generate migration AddDefaultValueToFoo

Modify new migration (for ex. myattribute has a string type) like this:

class AddDefaultValueToFoo < ActiveRecord::Migration
def self.up
change_column :foos, :myattribute, :string, :default => "value"
Foo.update_all(:myattribute => "value")
end
end