My title might be confusing, I wasn't sure what to write.
In rails I understand how to fetch Many Objects for One parent object
#first_user = User.first
#first_user_posts = #first_user.posts
But how can I fetch Many Objects for Many parent objects and select its attributes in one query?. I am trying to do something like that:
#many_posts = Post.all
#posts_by_user_gender = #many_posts.joins(:user).map(&:gender)
hoping it would give me an array that could look something like this:
#posts_by_user_gender => ["male", nil, "female", nil]
#I know I can do this map technique if I fetch it directly from the User model
# User.all.map(&:gender),
# but I want to start with those that posted in a specific category
# Post.where(:category_id => 1)
and then to count the males I could use the Ruby Array method .count
#males_count_who_posted = #posts_by_user_gender.count("male")
=> 1
I could always do 3 separate queries
#males_count_who_posted = #many_posts.select(:user_id).joins(:user)
.where("gender = ?", "male").count
#females_count_who_posted = ...
but I find that extremely inefficient, especially if I do the same for something like "industry" where you could have more than 3 options.
you can join model via SQL syntax
#posts_by_user_gender = #many_posts.joins("LEFT JOIN Users where users.id=posts.user_id").joins("LEFT JOIN Genders where genders.id=user.gender_id")
Related
Newbie Rails developer here so please bare with me.
I have a table called Ingredients where it contains a title field and an association to a User. A user can have many ingredients.
I want to query the database to get the ingredients that are not already available to a User.
I tried doing something like this with Rails:
#ingredients = current_user.ingredients
#community_ingredients = Ingredient.all.excluding(#ingredients).pluck(:title, :id)
But the problem is that this still returns values that are the same & only the case is different.
How can I achieve this outcome?
Try following queries.
#community_ingredients = Ingredient.includes(:user).where("users.user_id = ?", current_user.id).where(users: { id: nil } ).pluck(:title, :id)
OR
Ingredient.includes(:user).where("users.user_id = ?", current_user.id).where(ingredients: {user_id: nil } ).pluck(:title, :id)
OR
Ingredient.includes(:user).where("users.user_id = ?", current_user.id).where(users: { ingredient_id: nil } ).pluck(:title, :id)
Choose right query based on your association and feel free to suggest me so I can remove the extra one.
Most probably the first or second query will work, I strongly feel the third might not be the case.
Let's say this one is not working for you and you want to have solution based on your architecture.
#ingredients = current_user.ingredients.pluck(:title)
#community_ingredients = Ingredient.where.not("lower(title) IN (?)", #ingredients.map(&:downcase)).pluck(:title, :id)
So basically we need to convert both column value and the matching list in same case.
So we have converted to downcase.
here is how it looks in my local system, just make sure it's working that way.
I have 2 ActiveRecords: Article and Tag, in a many to many relationship. Basically I want to know how to select with a CONTAINS or LIKE condition, ie. to define a condition on a many to many relationship to contain a specified subset within an array.
The code structure I am trying to work out is as follows:
tag_names = ["super", "awesome", "dope"]
tags = Tag.where("name IN (?)", tag_names)
# The following is my non-working code to illustrate
# what I'm trying to do:
articles = Article.where("tags CONTAINS (?)", tags)
articles = Article.joins(:tags).where("articles.tags CONTAINS (?)", tags)
If you have different tables then you have to use joins and then specify a condition on your join:
Article.joins(:tags).where('tags.id IN ?', tag_ids)
If you want more flexibility on you queries, you could also use Arel and write something like the following:
tags = Tag.arel_table
tags_ids = Tag.where(tags[:name].matches("%#{some_tag}%"))
Article.joins(:tags).where(tagss[:id].in(tags_ids))
You can read more about matches in this answer.
I prefer Arel conditions over pure String or even Hash conditions.
I have a "Stores" model that contains various locations. Among the attributes for each store is the the "brands" that is carries.
Example: Store1, brands: "Nike, Adidas, Polo"; Store2, brands: "Jcrew, Polo"
I want to be able to select all stores where brand contains "Adidas" (may also contain other brands)
Something along the lines of:
#search = Stores.where(brands: params[:brand])
but need it to be
#search = Stores.where(brands.include? params[:brand])
which clearly doesn't work
What's the best way to deal with this?
If brands is a string and params[:brand] contains a single brand name, you can use MySQL's LIKE function:
#search = Stores.where(['BRANDS LIKE ?', "%#{params[:brand]}%"])
You can do this with the following statement.
#search = Stores.where("brands = ?", params[:brand])
A similar example is given in Listing 11.43 of the Hardtl rails tutorial
You should also note that rails models generally are meant to have singular names, i.e. Store instead of Stores.
I'm using rails and am trying to figure out how to use ActiveRecord within the method to combine the following into one query:
def children_active(segment)
parent_id = Category.select('id').where('segment' => segment)
Category.where('parent_id'=>parent_id, 'active' => true)
end
Basically, I'm trying to get sub categories of a category that is designated by a unique column called segment. Right now, I'm getting the id of the category in the first query, and then using that value for the parent_id in the second query. I've been trying to figure out how to use AR to do a join so that it can be accomplished in just one query.
You can use self join with a alias table name:
Category.joins("LEFT OUTER JOIN categories AS segment_categories on segment_categories.id = categories.parent_id").where("segment_categories.segment = ?", segment).where("categories.active = ?", true)
This may looks not so cool, but it can implement the query in one line, and there will be much less performance loss than your solution when data collection is big, because "INCLUDE IN" is much more slower than "JOIN".
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.