How can I iterate through an array of Activerecord::Relation objects? For instance, let's say I have a Comment class and a User class and I'd like to get all the comment contents from 3 specific users (assuming comments belong to users and user_id is the foreign key):
>> #males = Comment.where('user_id IN (?)', ["123","456","789"])
=> [...] #Array of comment Activerecord::Relation objects
Now I'd like to iterate through comments_from_males and collect all the content attribute contents for each comment in the array.
To clarify, the following works but only for the first male returned, but I need all the comments for all males:
>> #males.first.comments.map(&:content)
=> ["first comment", "second comment"]
comments = #males.map {|user| user.comments.map(&:content)}.flatten
Comment.where('user_id IN (?)', ["123","456","789"]).pluck(:content)
The method pluck
You can use
comments_from_males = #males.collect{|e| e.content if e.gender == "male"}.flatten
It will give you list of all comments from males. Check my db assumptions match.
Related
I have prepare these two arrays:
list_of_students = Student.where('class = ?', param[:given_class])
list_of_teachers = Teacher.where(...)
Student belongs_to Teacher and Teacher has_many students.
And now, I'd need to remove from the list_of_students all items (students), where teacher_id is not included in list_of_teachers.
I found some tips and HOWTO's on comparing arrays, but none of that helped to figure out this case.
Thank you in advance
You can use the IN SQL statement.
list_of_students = Student.where('class = ? AND teacher_id IN (?)', param[:given_class], list_of_teachers.map(&:id))
If the list_of_teachers is an ActiveRecord::Relation (and not an array), you can also use #pluck(:id) or (from Rails 4) #ids
Student.where('class = ? AND teacher_id IN (?)', param[:given_class], list_of_teachers.ids)
There are several ways to write the IN statement. Given you already have a where, I joined it to the main where. But you could also write
Student.where('class = ?', param[:given_class]).where(teacher_id: list_of_teachers)
or
Student.where(class: param[:given_class], teacher_id: list_of_teachers)
Also note you don't need to assign the list of teachers to a variable.
Student.where(class: param[:given_class], teacher_id: Teacher.where(...).ids)
Last but not least, if your Teacher query is simple, you may want to use a single query and a JOIN. Assume you want to get all the Teachers with name Rose.
Student.where(class: param[:given_class], teacher_id: Teacher.where(name: 'Rose').ids)
You can rewrite the same query to
Student.where(class: param[:given_class]).joins(:teacher).where(teacher: { name: 'Rose' })
or (the final and shorter expression)
Student.joins(:teacher).where(class: param[:given_class], teacher: { name: 'Rose' })
You can try something like
a = [1,2,3]
b = [1,4,5]
pry(main)> a.delete_if {|a1| !b.include? a1}
=> [1]
it checks each value in a is in b or not. If not it deletes the value from a and gives you a array finally.
This is an example. You can use this accordingly
I have a object User and object Post. A User has_many Posts and a Post belongs_to a User.
I can access the posts a user has using syntax like:
posts = #user.posts
However, I want to generate an array of ids of the posts a user owns, without looping through each one. Ideally, I'd like to do this:
ids = #user.posts.id
However, I get an error, saying that id is an invalid method for ActiveRecord--etc etc...
Is there any way to neatly do this without having to do a loop like:
ids = []
posts = #user.posts
posts.each |post| do
ids << post.id
end
Rails provides a native method for this:
#user.post_ids
Essentially, you can refer to the ids of a has_many association using <singular association name>_idspattern.
Try with ids = posts.map(&:id) or ids = posts.map{|p| p.id }
You can also try with ids = posts.pluck(:id)
You Can also use collect.
Collect returns the Array.
ids = #user.posts.collect(&:id)
try this :
#ids = #user.posts.map{|x| x.id }
Hope it will help.
I have been scratching my head over this one for a little while, and though I'm sure its a stupid mistake, I've reached the point where I must consult SO if I am to preserve the hair follicles I have left.
I've written a function in Rails (3.1.2) which should return an array populated with ActiveRecord model objects (users, in this case) which meet a certain criterion. The criterion is that the user's current list (denoted by the field active_list_id) must not be nil. The code follows:
def build_list_array
#lists = Array.new
User.all.each do |user|
#active_list_id = user.active_list_id
#lists<< List.find(#active_list_id) if #active_list_id != nil #TODO WHAT?!? WHY IS THIS RETURNING USERS?
end
end
As you can see, I'm initializing an empty array, cycling through all users and adding their active list to the array if the relevant reference on the user record is not nil. The problem is, this is returning user objects, not list objects.
Here are the associations from the user and list models:
user model:
has_many :lists
has_many :tasks
list model:
belongs_to :user
A brief word about the reference to active_list: A user can have many lists, but only one is active at any time. Therefore, I need to reference that list on the user record. The active list is not a foreign key in the typical sense, then.
I appreciate any help you can give me...Thanks =)
As it stands, your build_list_array will return an array of User because of the behavior of each. When iterating over a collection using each, the call to each returns the original collection.
For example,
list = []
# returns => []
[1,2,3,4,5].each { |number| list << number * 10 }
# returns => [1, 2, 3, 4, 5]
list
# returns => [10, 20, 30, 40, 50]
In your code, the last statement in your build_list_array method is the each call, meaning the return value of each is what is returned by the method. If you simply added a return statement at the end of the method you would be good to go.
def build_list_array
#lists = Array.new
User.all.each do |user|
#active_list_id = user.active_list_id
#lists<< List.find(#active_list_id) if #active_list_id
end
return #lists # Actually return #lists
end
That being said, you should probably use something like Bradley's answer as a basis for more "correct" Rails code.
each always returns the collection it iterates on (no matter what happens inside the block). Sounds like you want to return #lists at the end of your method.
You seem to be making a curious use of instance variables. You could also fetch this in one query via a join, something along the lines of
List.joins('inner join users on active_list_id =lists.id')
Activerecord's Arel is your friend here:
User.where(:active_list_id.not_eq => nil)
Extending Steven's answer, to get the Lists
class User
belongs_to :active_list, :class_name => "List"
def build_list_array
#lists = User.where('active_list_id is not null').map(&:active_list).compact
I'll explain this as best as possible. I have a query on user posts:
#selected_posts = Posts.where(:category => "Baseball")
I would like to write the following statement. Here it is in pseudo terms:
User.where(user has a post in #selected_posts)
Keep in mind that I have a many to many relationship setup so post.user is usable.
Any ideas?
/EDIT
#posts_matches = User.includes(#selected_posts).map{ |user|
[user.company_name, user.posts.count, user.username]
}.sort
Basically, I need the above to work so that it uses the users that HAVE posts in selected_posts and not EVERY user we have in our database.
Try this:
user.posts.where("posts.category = ?", "Baseball")
Edit 1:
user.posts.where("posts.id IN (?)", #selected_posts)
Edit 2:
User.select("users.company_name, count(posts.id) userpost_count, user.username").
joins(:posts).
where("posts.id IN (?)", #selected_posts).
order("users.company_name, userpost_count, user.username")
Just use the following:
User.find(#selected_posts.map(&:user_id).uniq)
This takes the user ids from all the selected posts, turns them into an array, and removes any duplicates. Passing an array to user will just find all the users with matching ids. Problem solved.
To combine this with what you showed in your question, you could write:
#posts_matches = User.find(#selected_posts.map(&:user_id).uniq).map{ |user|
[user.company_name, user.posts.size, user.username]
}
Use size to count a relation instead of count because Rails caches the size method and automatically won't look it up more than once. This is better for performance.
Not sure what you were trying to accomplish with Array#sort at the end of your query, but you could always do something like:
#users_with_posts_in_selected = User.find(#selected_posts.map(&:user_id).uniq).order('username DESC')
I don't understand your question but you can pass an array to the where method like this:
where(:id => #selected_posts.map(&:id))
and it will create a SQL query like WHERE id IN (1,2,3,4)
By virtue of your associations your selected posts already have the users:
#selected_posts = Posts.where("posts.category =?", "Baseball")
#users = #selected_posts.collect(&:user);
You'll probably want to remove duplicate users from #users.
I want to do something like this:
Given:
#user1
#user2
Where the Post model has (id, user_id)
#posts = #user1.posts
I want to take all of the posts of user1, and set the user_id to #user2
Is there an easy one liner way to do this? Or do I have to loop through all the #posts and update attributes and save the record?
Thanks
You can use the class method update_all on your Post class to accomplish this. The first string passed is essentially the SET clause of an SQL update statement, the second string is the WHERE clause.
Post.update_all("user_id = #{#user2.id}", "user_id = #{#user1.id}")
I use the _ids attribute for this.
#user2.update_attribute(:post_ids, #user1.post_ids)
More explanation
If you type
#user1.post_ids # --> [1,2,3,4]
You will get all the ids for all the posts the user is connected to in an array.
You can also set the relationship in this way too
#user2.post_ids = [1,2]
#user2.save
So, to solve what you are asking about I simply assigned the array of post ids of #user1 to the post ids for #user2.