update fail - undefined method `update_attributes' for #<ActiveRecord::Relation:

问题

This follows on from my previous request which I answered. But my next issue which I cannot understand is why when my parameters report one record do I get a message that googling/SO searching suggest I need to use an update_all.

has_many/belongs_to build association - why is insert statement for parameter blank?

My update controller method is as follows:

  def update
    @role = Role.find(params[:id])
    logger.debug "@role: id[#{params[:id]}], #{@role}, #{@role.inspect}, #{@role.to_s}"
    @permission = @role.permissions(params[:permission])
    logger.debug "@permission: #{@permission.inspect}"

    respond_to do |format|
      if @role.update_attributes(params[:role]) && @permission.update_attributes(params[:permission])
        format.html { redirect_to @role, notice: 'Role was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: "edit" }
        format.json { render json: @role.errors, status: :unprocessable_entity }
      end
    end
  end

I get the following error message:

 NoMethodError in RolesController#update

undefined method `update_attributes' for #<ActiveRecord::Relation:0x007fb2116b5178>

Rails.root: /Users/railsdev/Development/railsprojects/Genie/BitBucket-Repos/Genie-v3-3
Application Trace | Framework Trace | Full Trace

app/controllers/roles_controller.rb:75:in `block in update'
app/controllers/roles_controller.rb:74:in `update'

Request

Parameters:

{"utf8"=>"✓",
 "_method"=>"put",
 "authenticity_token"=>"3uZ47itmgzUSs83Iq9+2saJn6Y9+Y9tlSDgaRskh9pw=",
 "role"=>{"description"=>"T1"},
 "permission"=>{"subject_class"=>"User"},
 "commit"=>"Update Role",
 "id"=>"55"}

Googling and SO searches reveal that I may need to use [update_all] instead. But why when I only have a single record is this the case?

Here is my console output.

Started PUT "/roles/55" for 127.0.0.1 at 2012-10-01 22:12:16 +0100
Processing by RolesController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"3uZ47itmgzUSs83Iq9+2saJn6Y9+Y9tlSDgaRskh9pw=", "role"=>{"description"=>"T1"}, "permission"=>{"subject_class"=>"User"}, "commit"=>"Update Role", "id"=>"55"}
  User Load (0.2ms)  SELECT "users".* FROM "users" WHERE "users"."remember_token" = 'gn668LQGNlLl6HiwPf8DRQ' LIMIT 1
  Role Load (0.1ms)  SELECT "roles".* FROM "roles" INNER JOIN "assignments" ON "roles"."id" = "assignments"."role_id" WHERE "assignments"."user_id" = 13
  Role Load (0.1ms)  SELECT "roles".* FROM "roles" WHERE "roles"."id" = ? LIMIT 1  [["id", "55"]]
@role: id[55], #<Role:0x007fb2137e3200>, #<Role id: 55, description: "T1", created_at: "2012-10-01 21:11:43", updated_at: "2012-10-01 21:11:43">, #<Role:0x007fb2137e3200>
  Permission Load (0.1ms)  SELECT "permissions".* FROM "permissions" WHERE "permissions"."role_id" = 55
@permission: [#<Permission id: 32, role_id: 55, subject_class: "Diagnosis", action: nil, subject_id: nil, created_at: "2012-10-01 21:11:43", updated_at: "2012-10-01 21:11:43">]
  Permission Load (0.1ms)  SELECT "permissions".* FROM "permissions" WHERE "permissions"."role_id" = 55
Completed 500 Internal Server Error in 5ms

NoMethodError (undefined method `update_attributes' for #<ActiveRecord::Relation:0x007fb2116b5178>):
  app/controllers/roles_controller.rb:75:in `block in update'
  app/controllers/roles_controller.rb:74:in `update'

To aid in my debugging I have logged the following:

@role: id[55], #<Role:0x007fb2137e3200>, #<Role id: 55, description: "T1", created_at: "2012-10-01 21:11:43", updated_at: "2012-10-01 21:11:43">, #<Role:0x007fb2137e3200>

@permission: [#<Permission id: 32, role_id: 55, subject_class: "Diagnosis", action: nil, subject_id: nil, created_at: "2012-10-01 21:11:43", updated_at: "2012-10-01 21:11:43">]

Is it because one is 'wrapped' as an array? [output of the @permission logger.debug call]. Is this the indicator that I should be using the update_all?

回答1:

Yes, #where() returns an ActiveRecord::Relation, which can represent multiple records. You may just want to use @role.permissions(params[:permission]).first.update(...) instead of update_all, since you only intend to update a single row.

Also, I noticed that you're implementing a permissions/role model. May I suggest a gem for this purpose since this has been reimplemented many times? Something like cancan/cantango, perhaps?

来源：https://stackoverflow.com/questions/12681371/update-fail-undefined-method-update-attributes-for-activerecordrelation