Rails：通过表单中的对象 ID 数组进行 has_many 关联

Question

I have a model Group which has_many Users .

class Group < ApplicationRecord
  belongs_to :user
  has_many :users
  serialize :user_ids, Array
end

I'm using JS on the front end to add User ids to an array user_ids . The hidden field looks as such:

 = f.hidden_field :user_ids, id: "ids_field"

After selecting a few users, adding them to a JS array and assiginging the value of the hidden field to t hat array,I submit using strong params (with user_ids as an array) to create a new object from the params:

@group = Group.new(group_params)

---

def group_params
  params.require(:group).permit(:name, :user_id, :user_ids=>[])
end

The log shows a commit with the user_ids in a comma-delimited list:

Processing by GroupsController#create as JS

Parameters: {"utf8"=>"✓", "group"=>{"name"=>"", "user_ids"=>["25,1"]}, "commit"=>"Save Squad"}

Inspecting the Group in the console shows that only the first ID in the array gets assigned to the Group.

irb(main):128:0> Group.last.user_ids
..
[
    [0] 25
]

I've been bashing my head against the wall on this problem for the last two days and simply cannot make it work. I've tried variations of: - using JSON on the front end - removing serialization on the backend - splitting the array param using.split(",") - playing around with the group_params, including / excluding "=>[]" on user_ids and adding explicit name to my hidden field. Often I would get an un-permitted parameters error here. - Assigning the array to the group model using Group.users <<....

Any help or direction is greatly appreciated. I feel like I have gotten all parts correct at some point, just not at the same time. If i'm totally off and there is a better way to do this, I'm ready to ditch this and move on.

Thank you in advance:)

---

Edit : More playing around has shown me that the user_ids array is indeed an array, but only consists of one entry: "25,1". I solved my problem by taking params[:user_ids][0] and splitting it by comma delimiter, looping through the indices, and saving each one of those users to the group association. I don't think this is a great solution and still would like to pass the straight array in without manipulation.

Answer 1

This seems like the classic Has and Belongs to Many situation, as a User can "own" a Group and belong to many Groups. I would do something along the lines of:

class Group < ApplicationRecord
  belongs_to :user
  has_many :users_groups
  has_many :users, through: :users_groups
  accepts_nested_attributes_for :users
end

Class User < ApplicationRecord
  belongs_to :group
  has_many :users_groups
  has_many :groups, through: :users_groups
  accepts_nested_attributes_for :groups
end

in your terminal create a migration:

rails g migration CreateUsersGroupsJoinTable users groups

This will create a join table with columns:

|id|user_ids|group_ids|

This gets you all sorts of Rails methods like:

u = User.find(1)
 #returns user with ID 1

u.groups
 #will a result of joining Group with UsersGroups ON groups.id = users_groups.group_id WHERE users_groups.user_ids = 1

You can do the reverse too:

g = Group.find(1)

g.users
 #returns all user objects that belong to that group.

Then when you are doing forms it gives you things like collection_check_boxes that will automatically build out checkboxes based on things like Group.all or User.all, returning an array that will automatically update the join table and do all of this work it looks like you are doing in JS.

Answer 2

Though there is an answer, I think the real problem is

"user_ids"=>["25,1"]

should be

"user_ids"=>["25", "1"]

On the front end I use JS to combine a comma-delimited string like

"25,1"

And in the controller I use Ruby to parse it into an array

params[:user_ids].split(",").uniq

And I can just assign it to the instance. Rails will create associations.

group.user_ids = params[:user_ids].split(",").uniq