ruby on rails在表中添加列的最佳方法是什么

Question

My question is about finding a convenient way to add, remove, rename and change type of columns in a SQLite data structure.

I have a Ruby on Rails form that has multiple input text fields like the following (simplified):

<%= form_for(@Product, :html => {:name => "product_name", :id => "product_id"}) do |form| %>
    <div class="field">
        <%= form.flag "Input 1" %>
        <%= form.text_field :Input_1 %>
        <%= form.flag "Input 2" %>
        <%= form.text_field :Input_2 %>
        ..., etc.
    </div>
<% end %>

So far, I followed the procedure described in RoR Migration Guide, so every time I needed to add a new text field, say Input n, I generated a migration for it, like this

rails generate migration AddInputToProducts Input_n:string

then I ran the migration

rake db:migrate

The problem with this procedure is that once the migration is generated and ran, I no more have a trace of the exact name I used for the migration (Input_n in this example) unless I immediately create an entry for it in my RoR form and keep it there for ever. The results is that my table now has multiple entries I created thinking I would use them but I actually don't need them anymore, I don't remember their exact name and I'd like to either remove, re-use, rename or change their type.

My question is twofold:

1. Is there is a better and more convenient way to add columns to an existing table that would be more practical than running migrations as described in the guide?
2. How can I list, remove, rename or change type of existing columns in my data structure?

Answer 1

If you look in the db folder there is a file named schema.rb which have all the information about your tables including the names of the columns. There is the list.

For removing, renaming etc, migrations are perfect, but there is nothing stopping you from using other tools like Mysql Query browser (granted you are using MySQL).

Answer 2

如果您不想使用该工具进行迁移，则可以为所使用的数据库（SQLite）使用GUI，也可以在那里进行更改。

Answer 3

Whenever you generate a migration, an associated file is created in db/migrate that you can inspect and adjust as required. As a matter of convention it's usually bad form to alter a migration that has already been applied. If you need to make changes, either unapply the migration if it's only been applied to your machine with rake db:migrate:down VERSION=nnn where nnn is the version serial, or create a second migration that undoes the first.

The more complicated your development and deployment environment is, the more careful you will have to be with managing your migrations.

If you don't care about your data, you can always rake db:migrate:reset to build from the ground up. I do this often during the early stages of development when fine-tuning the database structure. Once I get it working I'll then commit it and make additional migrations to alter it from that point forward. Remember that reset will effectively drop and recreate your database, so don't ever run this on a production system.