Ruby-on-rails 如何从我的 Rails 模型中删除一列？
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How to remove a column from my Rails model?
提问by Hemanth
I need to remove a few columns from my rails model which i already created and have some row entries in that model. How to do it? Any links which has details for modifying the schema in rails ? I'm using rails version 3.
我需要从我已经创建的 Rails 模型中删除几列，并在该模型中有一些行条目。怎么做？任何包含在 rails 中修改架构的详细信息的链接？我正在使用 Rails 版本 3。
回答by Jason stewart
To remove a database column, you have to generate a migration:
要删除数据库列，您必须生成迁移：
script/rails g migration RemoveColumns
Then in the self.up class method, remove your columns:
然后在 self.up 类方法中，删除您的列：
def self.up
remove_column :table_name, :column_name
end
You may want to add them back in the self.down class method as well:
您可能还想将它们添加回 self.down 类方法中：
def self.down
add_column :table_name, :column_name, :type
end
The Rails Guidefor this goes into much more detail.
在Rails的指南此进入更多的细节。
回答by slm
If you know the columns you want to remove you can use the convention: Remove..From.. when naming your migrations. Additionally you can include the column names when running the migration command.
如果您知道要删除的列，则可以在命名迁移时使用约定：Remove...From...。此外，您可以在运行迁移命令时包含列名称。
The form of the command:
命令的形式：
rails g migration Remove..From.. col1:type col2:type col3:type
For example:
例如：
rails g migration RemoveProjectIDFromProjects project_id:string
generates the following migration file:
生成以下迁移文件：
class RemoveProjectIdFromProjects < ActiveRecord::Migration
def self.up
remove_column :projects, :project_id
end
def self.down
add_column :projects, :project_id, :string
end
end
回答by Gediminas
Via command alternative as Add, only change Addto Remove:
通过命令替代 as Add，只更改Add为Remove：
Single Column:
单列：
rails g migration RemoveColumnFromTable column:type
Multiple Columns:
多列：
rails g migration RemoveColumn1AndColumn2FromTable column1:type colummn2:type
