How rails interprets params hash, strict parameters

Question

At first, when I was creating posts, the user id was nil. Originally my post_params were just :content & :category. It wasn't until I added :user_id that I was finally able to get post.user.first_name to work properly.(first_name is a User column) I screwed around a lot with it and at one point when I was creating posts, the id would show up, but then on a refresh of the page, the id would disappear(I am using ajax to show the post after submit). The params still do not include :user_id, but now when the post is created and put into the db, the user_id is there. I am not explicitly saying what the user_id is, so how does it know? from the before_authentication! filter from devise? Or does it get the id from current_user.posts.create?

Originally had

def  create  
@post=post.create({content: post_params[:content], category:   post_params[:category].downcase})
end

then...

def create
@post = current_user.posts.create({content: post_params[:content], category:   post_params[:category].downcase})
end

private

def post_params
params.require(:post).permit(:content, :category, :user_id)
end


User Load (0.2ms)  SELECT  "users".* FROM "users"  WHERE "users"."id" = 6  ORDER BY  "users"."id" ASC LIMIT 1
 (0.1ms)  begin transaction
SQL (0.3ms)  INSERT INTO "posts" ("category", "content", "created_at", "updated_at",   "user_id") VALUES (?, ?, ?, ?, ?)  [["category", "announcements"], ["content", "Hi All!"],  ["created_at", "2014-10-13 19:58:02.937604"], ["updated_at", "2014-10-13 19:58:02.937604"],  ["user_id", 6]]
(3.8ms)  commit transaction
Like Exists (0.2ms)  SELECT  1 AS one FROM "likes"  WHERE "likes"."user_id" = 6 AND   "likes"."post_id" = 69 LIMIT 1

Answer 1

while you call create or build on a relationship (posts of user in this case) Rails automatically instanciate the good relationship field to link the object to the parent.