问题
For a Rails 3.0 Todo app, I have a Tasks model with a Status field. What's the best way to store the Status field data (field type) and still display a human-readable version in a view (HTML table)? Status can be:
0 = Normal
1 = Active
2 = Completed
Right now I have this:
Rails Schema Here:
create_table "tasks", :force => true do |t|
t.integer "status", :limit => 1, :default => 0, :null => false
Rails Model Here:
class Task < ActiveRecord::Base
validates_inclusion_of :status, :in => 0..2,
:message => "{{value}} must be 0, 1, or 2"
Rails View Here:
<h1>Listing tasks</h1>
<table>
<tr>
<th>Status</th>
<th>Name</th>
<th></th>
<th></th>
<th></th>
</tr>
<% @tasks.each do |task| %>
<tr>
<td><%= task.status %></td>
<td><%= task.name %></td>
<td><%= link_to 'Show', task %></td>
<td><%= link_to 'Edit', edit_task_path(task) %></td>
<td><%= link_to 'Delete', task, :confirm => 'Are you sure?', :method => :delete %></td>
</tr>
<% end %>
</table>
Requirements
Store a Task's status in the db such that the values are easily localizable, i.e. I'm not sure I want to store "normal", "active", "completed" as a string field.
Solution must work with Rails 3.0.
Questions:
Should I store the field as an integer (see above)? If so, how do I display the correct human readable status in an HTML table in my Rails view, e.g. show "Active" instead of "1" in the HTML table.
Should I use an enum? If so, is this easy to localize later?
Should I use straight strings, e.g. "Normal", "Active", "Completed"
Can you provide a quick code sample of the view helper, controller or view code to make this work?
回答1:
1.It depends on how much you want to optimize queries on the DB.
2.Not really, it is not supported 'out of the box' by AR. # As of Rails 4 enums are supported out of the box.
3.IMHO you can use strings without a big performance penalty (just remember to add field to an index). I would do this because it's easier to internationalize and to maintain. However, you can go with integers if you need extra performance.
You may take a look on 2 SO threads here and here where this is debated.
4.If you want to keep them as integer, here is how you can accomplish this:
class Task << AR::Base
NORMAL = 1
ACTIVE = 2
COMPLETED = 3
STATUSES = {
NORMAL => 'normal',
ACTIVE => 'active',
COMPLETED => 'completed'
}
validates_inclusion_of :status, :in => STATUSES.keys,
:message => "{{value}} must be in #{STATUSES.values.join ','}"
# just a helper method for the view
def status_name
STATUSES[status]
end
end
and in view:
<td><%= task.status_name %></td>
If you want to use strings, it's more simplified:
STATUSES = ['normal', 'active', 'completed']
validates_inclusion_of :status, :in => STATUSES,
:message => "{{value}} must be in #{STATUSES.join ','}"
回答2:
The easiest thing to do would be to just store the actual strings in the field instead of adding another table. Depending on your point of view this is either a bad idea as your database will not be sufficiently normalized or a great idea as your app is now more efficient for being normalized.
If you opt to not do that and to keep the values in a separate table; you need to setup the relationships in the model.
class Task < ActiveRecord::Base
has_one :status
end
class Status < ActiveRecord::Base
belongs_to :tasks
end
Then in your view you can reference the value by:
<%= task.status %>
回答3:
I have used Enum-Column for such use cases. The plugin allows you to define a enum column type in your migration script and creates a MYSQL enum column type for the attribute.
create_table :tasks do |t|
...
t.enum :status, :limit => [:normal, :active, :completed], :default => :normal
...
end
Now in your code you can do the following:
task.status = "active"
task.status = :completed
p "Task status: #{task.status}" # prints Task status: completed
Task.find_by_status(:active)
Task.find_by_status("active")
Task.find_by_status(2)
Works well with serialization too:
task.to_xml # will result in status= active instead of status-2
Other nice aspect is, the status values are displayed as strings when viewed using a regular DB client(E.g: mysql command console or phpMyAdmin)
The plugin provides optimal storage and user friendly access for the enumeration types.
Caveat:
The plugin is quite old and not maintained. I am using it extensively with MySQL DB. I had to patch the code to get it work on PostgreSQL. If you are using MySQL, this plugin is a good choice.
回答4:
I prefer to store "normal", "active", .. "completed" as string in the table because:
- it's self documentation (for example, someone may look at the data but never read the Rails source code)
- there is little (if not no) performance penalty
- it is (still) easy to do i18n by means of Rails virtual attribute in the model or whatever layer in other languages
These days, I tend to decouple Rails constants from the database as much as I can. There are always some PHP/MSSQL/??DBA folks around us (who may not love Rails as much as we do ;-)
So, the answer is not integer nor enum (but a varchar ;-)
回答5:
I know this is an old question but I wanted to mention 2 points that come from experience, especially if someone is looking for this now ( 2014 - OQ was in 2010) :
- If you are starting a new project > Rails 4 ( technically ActiveRecord 4) - use Enums - the most efficient route. Especially if you need to create any kind of complicated SQL queries later on.
- There is on more alternative - create a composite Status model that will hold statuses for all your other models. Make it an STI model (add type column)- then you can create things like OrderStatus < Status or CustomerStatus < Status and your Order and Customer would have status_id attributes. This makes for slower (!) and more cumbersome (!) queries, however you might want to go this route if you are a creating an app that will be shipped to client that has no technical expertise and they would need some kind of ability to add / remove statuses through something like ActiveAdmin on their own rather than modify your code base. This is also an option if your data layer can't handle enums.
回答6:
Using integer to store the status is a good idea. Nonetheless, I think the code provided by the accepted answer is not elegant since it pollutes the whole model class just because of an attribute.
My suggestion is overriding the attribute getter:
def status
{
0 => "active",
1 => "inactive"
}[read_attribute(:status)] # use the read_attribute method to prevent infinite loop.
end
The logic of transforming the integer into a string will be only in this getter method, so you don't need to make the class dirty.
来源：https://stackoverflow.com/questions/2650897/in-rails-how-should-i-implement-a-status-field-for-a-tasks-app-integer-or-enu