I have a problem with filtering products by exact tags as my current query does not return exact matches and I can't seem to get the right query conditions.
Example
Area = ["small","big"] ,Surface = ["smooth","rough"]
Product A has only ["small","smooth","rough"] as tags
If I filter products using ["small","big","smooth","rough"] as the tags, I get product A in my search results but ideally, it should not return any search results.
I have three models, Product,Area and Surface. Area & Surface are linked to Product by a has_many through relationship.
class Product < ActiveRecord::Base
has_many :product_areas
has_many :areas, :through => :product_areas
has_many :product_surfaces
has_many :surfaces, :through => :product_surfaces
class Area < ActiveRecord::Base
#Surface model looks exactly the same as Area model
has_many :product_areas,dependent: :destroy
has_many :products, :through => :product_areas
My Query
area_ids = params[:area_ids]
surface_ids = params[:surface_ids]
#products = Product.where(nil)
#products = #products.joins(:areas).where('areas.id' => area_ids).group('products.id').having("count(areas.id) >= ?",area_ids.count) unless area_ids.blank?
#products = #products.joins(:surfaces).where('surfaces.id' => surface_ids).group('products.id').having("count(surfaces.id) >= ?",surface_ids.count) unless surface_ids.blank?
I solved this problem just now with this solution.
First I used the names of the models for Area & Surface as their unique identifer as they can have conflicting ids and added them to an array.
Next I looped through the products and created an array of the name identifers and compared the two arrays to check if they intersect. Intersection would mean that the search filters were a correct match and we add the product ID to a third array which stores all the product_ids before doing a query to get the products with those product ids.
#area = Area.all
area_ids = params[:area_ids]
#uniq_names = #area.where(id: area_ids).collect { |m| m.name }
#products.each do |product|
#names = product.areas.map { |m| m.name }
# if intersect, then we add them to filtered product
if (#uniq_names - #names).empty?
product_ids << product.id
end
end
#products = Product.where(id: product_ids)
Related
I have something like this:
duplicates = ['a','b','c','d']
if duplicates.length > 4
Photo.includes(:tags).where('tags.name IN (?)',duplicates)
.references(:tags).limit(15).each do |f|
returned_array.push(f.id)
end
end
duplicates is an array of tags that were duplicated with other Photo tags
What I want is to get Photo which includes all tags from duplicates array, but right now I get every Photo that include at least one tag from array.
THANKS FOR ANSWERS:
I try them and somethings starts to work but wasn't too clear for me and take some time to execute.
Today I make it creating arrays, compare them, take duplicates which exist in array more than X times and finally have uniq array of photos ids.
If you want to find photos that have all the given tags you just need to apply a GROUP and use HAVING to set a condition on the group:
class Photo
def self.with_tags(*names)
t = Tag.arel_table
joins(:tags)
.where(tags: { name: names })
.group(:id)
.having(t[:id].count.eq(tags.length)) # COUNT(tags.id) = ?
end
end
This is somewhat like a WHERE clause but it applies to the group. Using .gteq (>=) instead of .eq will give you records that can have all the tags in the list but may have more.
A better way to solve this is to use a better domain model that doesn't allow duplicates in the first place:
class Photo < ApplicationRecord
has_many :taggings
has_many :tags, through: :taggings
end
class Tag < ApplicationRecord
has_many :taggings
has_many :photos, through: :taggings
validates :name,
uniqueness: true,
presenece: true
end
class Tagging < ApplicationRecord
belongs_to :photo
belongs_to :tag
validates :tag_id,
uniqueness: { scope: :photo_id }
end
By adding unique indexes on tags.name and a compound index on taggings.tag_id and taggings.photo_id duplicates cannot be created.
The issue as I see it is that you're only doing one join, which means that you have to specify that tags.name is within the list of duplicates.
You could solve this in two places:
In the database query
In you application code
For your example the query is something like "find all records in the photos table which also have a relation to a specific set of records in the tags table". So we need to join the photos table to the tags table, and also specify that the only tags we join are those within the duplicate list.
We can use a inner join for this
select photos.* from photos
inner join tags as d1 on d1.name = 'a' and d1.photo_id = photos.id
inner join tags as d2 on d2.name = 'b' and d2.photo_id = photos.id
inner join tags as d3 on d3.name = 'c' and d3.photo_id = photos.id
inner join tags as d4 on d4.name = 'd' and d4.photo_id = photos.id
In ActiveRecord it seems we can't specify aliases for joins, but we can chain queries, so we can do something like this:
query = Photo
duplicate.each_with_index do |tag, index|
join_name = "d#{index}"
query = query.joins("inner join tags as #{join_name} on #{join_name}.name = '#{tag}' and #{join_name}.photo_id = photos.id")
end
Ugly, but gets the job done. I'm sure there would be a better way using arel instead - but it demonstrates how to construct a SQL query to find all photos that have a relation to all of the duplicate tags.
The other method is to extent what you have and filter in the application. As you already have the photos that has at least one of the tags, you could just select those which have all the tags.
Photo
.includes(:tags)
.joins(:tags)
.where('tags.name IN (?)',duplicates)
.select do |photo|
(duplicates - photo.tags.map(&:name)).empty?
end
(duplicates - photo.tags.map(&:name)).empty? takes the duplicates array and removes all occurrences of any item that is also in the photo tags. If this returns an empty array then we know that the tags in the photo had all the duplicate tags as well.
This could have performance issues if the duplicates array is large, since it could potentially return all photos from the database.
I think I want to do a union in Rails, but according to this post rails union hack, how to pull two different queries together unions aren't natively supported in Rails. I'm wondering if there is a better way to approach this problem.
I have table of items, each item has many prices, but I only want to join one price to each item.
To determine the proper price for an item I have two additional foreign keys in the price model: category_id and discount_id. Each could independently declare a price for an item.
Ex.
Item + Category = Price1 and Item + Discount = Price 2
If discount_id matches a passed id I want to exclude the price results FOR THAT ITEM ONLY that match Item + Category. Also I'm trying not to loose lazy loading.
Hopefully the problem is clear! If not I'll try to clarify more, thanks in advance.
Your models would start off looking something like this:
class Price < ActiveRecord::Base
belongs_to :item
belongs_to :category
belongs_to :discount
scope :category, where("prices.category_id IS NOT NULL")
scope :discount, where("prices.discount_id IS NOT NULL")
end
class Item < ActiveRecord::Base
has_many :prices
end
class Category < ActiveRecord::Base
has_many :prices
end
class Discount < ActiveRecord::Base
has_many :prices
end
One way of doing this is to add a class method to Price that encapsulates this logic:
class Price < ActiveRecord::Base
def self.used
discount_items_sql = self.discount.select("prices.item_id").to_sql
where("prices.discount_id IS NOT NULL OR prices.item_id NOT IN (#{discount_items_sql})")
end
end
This is effectively the same as this query:
SELECT * FROM prices
WHERE prices.discount_id IS NOT NULL -- the discount_id is present on this record,
OR prices.item_id NOT IN ( -- or no discount_id is present for this item
SELECT item_id FROM prices WHERE discount_id IS NOT NULL)
You can add these helper methods on your Item model for simplicity:
class Item < ActiveRecord::Base
def category_price
prices.category.first
end
def discount_price
prices.discount.first
end
def used_price
prices.used.first
end
end
Now you can easily get each individual 'type' of price for a single item (will be nil for prices that aren't available):
item.category_price
item.discount_price
item.used_price
I'm trying to increase my app's efficiency by doing work in the database rather than in the app layer, and I'm wondering if I can move this calculation into the database.
Models:
class Offer < ActiveRecord::Base
has_many :lines
has_many :items, :through => :lines
end
class Line < ActiveRecord::Base
belongs_to :offer
belongs_to :item
# also has a 'quantity' attribute (integer)
end
class Item < ActiveRecord::Base
has_many :lines
has_many :offers, :through => :lines
# also has a 'price' attribute (decimal)
end
What I want to do is calculate the price of an offer. Currently I have a price method in the Offer class:
def price
self.lines.inject(0) do |total, line|
total + line.quantity * line.item.price
end
end
I suspect it may be possible to do a Offer.sum calculation instead that would get the answer directly from the DB rather than looping through the records, but the Calculations section of the ActiveRecord query guide doesn't have enough detail to help me out. Anybody?
Thanks!
You're correct that you can do this with sum. Something like this:
class Offer < ActiveRecord::Base
# ...
def price
self.lines.sum 'lines.quantity * items.price', :joins => :item
end
end
When you call e.g. Offer.find( some_id ).price the above will construct a query something like this:
SELECT SUM( lines.quantity * items.price ) AS total
FROM lines
INNER JOIN items ON items.id = lines.item_id
WHERE lines.offer_id = <some_id>
;
Sometimes you're better off with SQL.
SELECT SUM( lines.quantity * items.price ) AS total
FROM offers
INNER JOIN lines ON offers.id = lines.offer_id
INNER JOIN items ON items.id = lines.item_id
WHERE offers.id = 1
;
I have three models: Products, Placements, Collections
I'm trying to write a name scope that only chooses products NOT in a certain collection.
products has_many :collections, :through => :placements
collections has_many :products, :through => :placements
I got about this far:
scope :not_in_front, joins(:collections).where('collections.id IS NOT ?', 4)
But that generated the opposite of what I expected in the query:
Product Load (0.3ms) SELECT "products".* FROM "products" INNER JOIN "placements" ON "products"."id" = "placements"."product_id" WHERE "placements"."collection_id" = 4
Any idea how to write this to only select the products not in that particular collection?
Instead of collections.id IS NOT 4 try collections.id != 4
The named scope was getting too ugly, so I went with this. Not sure it's the best way, but, it works...
def self.not_on_top_shelf
top_shelf = Collection.find_by_handle('top-shelf')
products = Product.find(:all, :order => "factor_score DESC")
not_on_top_shelf = products.map {|p| p unless p.collections.include?(top_shelf)}
not_on_top_shelf.compact #some products may not be in a collection
end
Lets assume I have a model Category which has_many Items. Now, I'd like to present a table of Categories sorted on various attributes of Items. For example, have the category with the highest priced item at the top. Or sort the categories based on their best rated item. Or sort the categories based on the most recent item (i.e., the category with the most recent item would be first).
class Category < ActiveRecord::Base
has_many :items
# attributes: name
end
class Item < ActiveRecord::Base
belongs_to :category
# attributes: price, rating, date,
end
Which is the best approach?
Maintain additional columns on the Category model to hold the attributes for sorting (i.e., the highest item price or the best rating of an item in that category). I've done this before but it's kinda ugly and requires updating the category model each time an Item changes
Some magic SQL incantation in the order clause?
Something else?
The best I can come up with is this SQL, for producing a list of Category sorted by the max price of the contained Items.
select categories.name, max(items.price) from categories join items group by categories.name
Not sure how this translates into Rails code though. This SQL also doesn't work if I wanted the Categories sorted by the price of the most recent item. I'm really trying to keep this in the database for obvious performance reasons.
Assuming the attributes listed in the items model are database columns there are many things you could do.
The easiest is probably named_scopes
/app/models/category.rb
class Category < ActiveRecord::Base
has_many :items
# attributes: name
named_scope :sorted_by_price, :joins => :items, :group => 'users.id', :order => "items.price DESC"
named_scope :sorted_by_rating, :joins => :items, :group => 'users.id', :order => "items.rating DESC"
named_scope :active, :condition => {:active => true}
end
Then you could just use Category.sorted_by_price to return a list of categories sorted by price, highest to lowest. The advantages of named_scopes lets you chain multiple similar queries. Using the code above, if your Category had a boolean value named active. You could use
Category.active.sorted_by_price to get a list of active categories ordered by their most expensive item.
Isn't that exactly what :joins is for?
Category.find(:all, :joins => :items, :order => 'price')
Category.find(:all, :joins => :items, :order => 'rating')