问题
I have tried a couple other similar posts but am still getting an error.
In the Posts model I have a category_id field. I have the following models:
#Posts model
belongs_to :categories
#Category model
has_many :posts
In the Posts index controller I have:
@categories = @posts.Category.find(:all, :order => 'categoryname')
In the View I have:
<% @posts.each do |post| %>
<tr>
<td><%= post.category_id %></td>
<td><%= @categories.categoryname %></td>
<td><%= link_to 'View', post %></td>
<td><%= link_to 'Edit', edit_post_path(post) %></td>
</tr>
<% end %>
In the 2nd column I am trying to show the category name ("categoryname") from the Category table instead of the category_id from the posts table. I am getting an error:
undefined method `Category' for #ActiveRecord::Relation:0x3e1a9b0>
I have also tried:
<td><%= post.categories.categoryname %></td>
But get the same error.
As well as:
<td><%= post.category.categoryname %></td>
Any suggestions would be greatly appreciated.
回答1:
In your model
belongs_to :category
In your view
<td><%= post.category.categoryname %></td>
You can get rid of the @categories = line in your controller
Also, categoryname is probably not the best attribute name for your Category model. Why not just name it name. post.category.name seems a lot better than post.category.categoryname, don't you think?
回答2:
Okay, a couple things
belongs_to :categories
belongs_to is a singular relationship. You should be putting
belongs_to :category
In this case you need category_id in the posts table. You would get the category by
@post.category.categoryname
Unless a post can have many categories, in which case you'd want
#Post
has_and_belongs_to_many :categories
#Category
has_and_belongs_to_many :posts
In this case you need a join table called categories_posts with two fields category_id and post_id and you would get it by calling
@post.categories.each do |cat|
cat.categoryname
end
There are some other problems with you code, like
@categories = @posts.Category.find(:all, :order => 'categoryname')
Category is a model, not your named relationship, which is probably why you are getting the exception in your application.
回答3:
You will get the following error
undefined method `categoryname' for nil:NilClass on the line: <%= post.category.categoryname %>
if there are records in your table without a category specified.
In other words, make sure all of your records have a category associated with them
回答4:
i Noticed that @category in your controller starts with a small letter c, but in your view, it starts with a Capital letter !
回答5:
In your case, if there is a chance that you can have an empty category_id in posts table (as you mentioned in your comment), you can add
if post.category_id?
so your cell will look like this:
<td><%= post.category.categoryname if post.category_id? %></td>
If post.category_id is null it will just show an empty cell.
来源：https://stackoverflow.com/questions/10762669/show-name-instead-of-id-in-has-many-view-table