我可以使用Model.find（params [：id]）。where（）之类的东西吗

Question

Hi, I am still a student and I'm taking a software engineering course and we have this big project (web design) and we're using rails so my question is I have a table Users and a table Groups and another association table GroupUsers where it has two foreign keys user_id and group_id . Whenever a user creates or join an already created group his id and the group_id are added to GroupUsers table

module GroupUsersHelper
   def join
      @group_id = params[:id]
      @user_id = params[:user_id]
      @newuser= GroupUser.new(:group_id => @group_id, :user_id => @user_id)
      @newuser.save
      redirect_to(:controller => 'groups', :action => 'show', :id => @group_id)
   end
end

Now I have to create method leave group where I'll have to destroy the record from GroupUsers , so I wrote this code also in GroupUsersHelper

  def leave
      @group_id = params[:group_id]
      @user_id = params[:user_id]
      @group_user_id = params[:group_user_id]
      @newuser= GroupUser.find(@group_user_id).where(:group_id => @group_id, :user_id =>
      @user_id)
      @newuser.destroy
      redirect_to(:controller => 'groups', :action => 'show', :id => params[:id])
   end

but I get this error

ActiveRecord::RecordNotFound in GroupsController#leave

Couldn't find GroupUser without an ID

If you need more info about the code please let me know.

Answer 1

Model.find(params[:id]) will generate such kind of query

 *Lets take an example : GroupUser.find(params[:id]) will generate sql equivalent*
 select * from group_users where id = params[:id]

If you want to add where condition do something like this
GroupUser.where("# id ={params[:id]} and someColumn = #{somevariable}")

Answer 2

You are not passing the groupuser_id in the params hash. Instead of storing it in the @group_id and @user_id , just try this:

@newuser= GroupUser.find_by_group_id_and_user_id(params[:group_id],params[:user_id])

Can you additionally post your params dump so we can figure out how to make a good redirect since i hence that will be a problem also.

Answer 3

Just do:

group = Group.find(params[:group_id])
user = User.find(params[:user_id])
group.users.delete(user)
group.save

This will remove the user from the users association, and will automatically destroy the GroupUser record when the group is saved. See the collection.delete method.

Answer 4

The other answers addressed your code example, but not the question in the title. You cannot use Model.find(params[:id]).where() in ActiveRecord (Rails' default ORM). Model.find returns a single record (an instance of your Model class) but Model.where returns a Model::ActiveRecord_Relation object (an array-like object). The .where method is only available on your Model class directly (ie Model.where ) or on an ActiveRecord_Relation. If you are chaining methods, you need to make sure each method returns an ActiveRecord_Relation. For example:

Model.where("name = ?", "max")
     .order(created_at: :desc)
     .reorder(created_at: :asc)
     .includes(:sent_comments)

Answer 5

@max pleaner is right, you should not use Model.find().where().

It is incorrect, and if you think about it, you will see that it is redundant. To find the association you wish to destroy, you either need params[:group_id] and params[:user_id], or just params[:group_user_id].

If you have passed the params[:group_user_id] to the leave method, you already have all the information needed to find the association:

def leave
  @newuser= GroupUser.find(params[:group_user_id])
  @newuser.destroy
  redirect_to(:controller => 'groups', :action => 'show', :id => params[:group_id])
end

Or alternatively, If you have passed the params[:group_id] and params[:user_id] to the leave method:

def leave
  @newuser= GroupUser.find_by_group_id_and_user_id(params[:group_id], params[:user_id])
  @newuser.destroy
  redirect_to(:controller => 'groups', :action => 'show', :id => params[:group_id])
end

Also, there are a few other redundancies in your code that you will notice I omitted above. There is no need to assign each parameter to an instance variable before passing the parameter to the find() method:

@model_id = params[:model_id]
@model= Model.find(@model_id)

#can be simplified to:

@model = Model.find(params[:model_id])

Generally, you only want to create instances variables for a record or collection of records you will need to access in a view (such as a Group in the context of your application).