Let's say I have models: User and Item and relation many-to-many between them. How to get Users who have exactly(no more) Items with the defined attributes i.e. Users who have Items with colors = ['red', 'black'].
Of course I can do something like this:
User.all :joins => [:items, :items], :conditions => {:"items.color" => "red", :"items_users.color" => 'black'}
But for more attributes it's going to be quite cumbersome.
I can do also:
User.all(:conditions => ["items.color in (?), ['red', 'black']], :include => :items)
But this one returns also users with items having colors = ['red', 'black', 'blue', 'etc']
So the only solution is to get all and to sort with ruby syntax ? How to do it in one SQL query or Rails AR syntax ?
The way which optimizes programmer time and readability, in my opinion:
#get all users who have items which are both red and black but no other colors
candidate_users = User.all(:include => :items)
candidate_users.reject! do |candidate|
candidate.items.map {|item| item.color}.sort != ['black', 'red']
end
If you are expecting to be looping through a metric truckload of users there, then you'll need to SQL it up. Warning: SQL is not my bag, baby: test before use.
select users.*, items.* FROM users
INNER JOIN items_users ON (items_users.user_id = users.id)
INNER JOIN items ON (items_users.item_id = items.id)
GROUP BY users.id HAVING COUNT(DISTINCT items.color) = 2
What I think that evil mess does:
1) Grabs every user/item combination
2) Winnows down to users who have items of exactly 2 distinct colors
Which means you'll need to:
candidate_users.reject! do |candidate|
candidate.items.map {|item| item.color}.sort != ['black', 'red']
end
You can probably eliminate the need for the ruby here totally but the SQL is going to get seven flavors of ugly. (Cross joins, oh my...)
Related
We have a Customer model, which has a lot of has_many relations, e.g. to CustomerCountry and CustomerSetting. Often, we need to join these relations to each other; e.g. to find the settings of customers in a given country. The normal way of expressing this would be something like
CustomerSetting.find :all,
:joins => {:customer => :customer_country},
:conditions => ['customer_countries.code = ?', 'us']
but the equivalent SQL ends up as
SELECT ... FROM customer_settings
INNER JOIN customers ON customer_settings.customer_id = customers.id
INNER JOIN customer_countries ON customers.id = customer_countries.customer_id
when what I really want is
SELECT ... FROM customer_settings
INNER JOIN countries ON customer_settings.customer_id = customer_countries.customer_id
I can do this by explicitly setting the :joins SQL, but is there an idiomatic way to specify this join?
Besides of finding it a bit difficult wrapping my head around the notion that you have a "country" which belongs to exactly one customer:
Why don't you just add another association in your model, so that each setting has_many customer_countries. That way you can go
CustomerSetting.find(:all, :joins => :customer_countries, :conditions => ...)
If, for example, you have a 1-1 relationship between a customer and her settings, you could also select through the customers:
class Customer
has_one :customer_setting
named_scope :by_country, lambda { |country| ... }
named_scope :with_setting, :include => :custome_setting
...
end
and then
Customer.by_country('us').with_setting.each do |cust|
setting = cust.customer_setting
...
end
In general, I find it much more elegant to use named scopes, not to speak of that scopes will become the default method for finding, and the current #find API will be deprecated with futures versions of Rails.
Also, don't worry too much about the performance of your queries. Only fix the things that you actually see perform badly. (If you really have a critical query in a high-load application, you'll probably end up with #find_by_sql. But if it doesn't matter, don't optimize it.
I'm pretty new to Rails, and the problem I'm bumping into is described as followes:
First, there is a table with houses.
The houses have multiple dates associated with has_many :dates
Second there is the table with dates.
Dates have the association belongs_to :house
Now, in a search, a user can select a start and end-date.
And what I want to do, is search each house for it's dates, and check if these are between the start and end-date. If one or more of the dates is within the start/end date, it needs to be found.
These are my conditions to search a house for other criteria:
parameters.push( [ params[:house_category_id], "houses.house_category_id = ?" ] );
parameters.push( [ params[:province_id], "houses.province_id = ?" ] );
I've created a method to create valid conditions with these parameters.
Please tell me, if it's not clear enough, cause it's a little hard to explain.
I've tried searching for this, but it got me on all kind of other pages except the pages with an answer..
Thanks
Not sure if I understand your problem correctly, but according to what I understood, you can get the desired result using the following:
res = House.find(:all, :select => 'distinct houses.*', :joins => "INNER JOIN dates ON dates.house_id = houses.id", :conditions => "dates.date < '2011-01-12' AND dates.date > '2011-01-11'")
where '2011-01-12' & '2011-01-11' are the dates selected by the user.
Let me know if this is what you were looking for or post with more details.
Now another question pops in my mind, but I don't know if that is possible..
If you forget about the from-to for this situation, is there any possibility that a I can check this sort of associations like so:
A house has 2 dates attached.
A User selects 2 dates.
Now I only want to select the house if these 2 dates both correspond..
Like this:
#houses = House.find(:all, :select => 'distinct houses.*', :joins => "INNER JOIN dates ON dates.house_id = houses.id", :conditions => "dates.date = '2011-01-12' AND dates.date = '2011-01-11'")
I tried the code above and got an SQL like this:
SELECT distinct houses.* FROM `houses` INNER JOIN dates ON dates.house_id = houses.id WHERE (dates.date = '2011-01-15' AND dates.date = '2011-01-22')
But it doesn't seem to work, is this possible at all in a single query or single find( )?
If i have two tables Books, CDs with corresponding models.
I want to display to the user a list of books and CDs. I also want to be able to sort this list on common attributes (release date, genre, price, etc.). I also have basic filtering on the common attributes.
The list will be large so I will be using pagination in manage the load.
items = []
items << CD.all(:limit => 20, :page => params[:page], :order => "genre ASC")
items << Book.all(:limit => 20, :page => params[:page], :order => "genre ASC")
re_sort(items,"genre ASC")
Right now I am doing two queries concatenating them and then sorting them. This is very inefficient. Also this breaks down when I use paging and filtering. If I am on page 2 of how do I know what page of each table individual table I am really on? There is no way to determine this information without getting all items from each table.
I have though that if I create a new Class called items that has a one to one relationship with either a Book or CD and do something like
Item.all(:limit => 20, :page => params[:page], :include => [:books, :cds], :order => "genre ASC")
However this gives back an ambiguous error. So can only be refined as
Item.all(:limit => 20, :page => params[:page], :include => [:books, :cds], :order => "books.genre ASC")
And does not interleave the books and CDs in a way that I want.
Any suggestions.
The Item model idea will work, but you are going to have to pull out all the common attributes and store them in Item. Then update all you forms to store those specific values in the new table. This way, adding a different media type later would be easier.
Update after comment:
What about a union? Do find_by_sql and hand-craft the SQL. It won't be simple, but your DB scheme isn't simple. So do something like this:
class Item < ActiveModel::Base
attr_reader :title, :genre, :media_type, ...
def self.search(options = {})
# parse options for search criteria, sorting, page, etc.
# will leave that for you :)
sql = <<-SQL
(SELECT id, title, genre, 'cd' AS media_type
FROM cds
WHERE ???
ORDER BY ???
LIMIT ???
) UNION
(SELECT id, title, genre, 'book' AS media_type
FROM books
WHERE ???
ORDER BY ???
LIMIT ???
)
SQL
items = find_by_sql(sql)
end
end
untested
Or something to that effect. Basically build the item rows on the fly (you will need a blank items table). The media_type column is so you know how to create the links when displaying the results.
Or...
Depending on how often the data changes you could, gasp, duplicate the needed data into the items table with a rake task on a schedule.
You say you can't change how books and CDs are stored in the database, but could you add an items view? Do you have any control over the database at all?
CREATE VIEW items
(id, type, title, genre, created_at, updated_at)
AS
SELECT b.id, 'Book', b.title, b.genre, b.created_at, b.updated_at
FROM books b
UNION
SELECT c.id, 'CD', c.title, c.genre, c.created_at, c.updated_at
FROM cds c;
You can paginate on a results array, so leave pagination out of the invidual model queries, and add it to your results array:
re_sort(items,"genre ASC").paginate(:page => params[:page], :per_page => items_per_page)
I have have 3 Tables of data and 2 Join Tables connecting everything. I'm trying to figure out a way to query the results based on the condition that the join table data is the same.
To explain, I have User, Interest, and Event Tables. These tables are linked through an HABTM relationship (which is fine for my needs since I dont need to store any other fields) and joined through two join tables. So i also have a UsersInterests table with (user_id, interest_id) and a EventsInterests table with (event_id, interest_id).
The problem comes when trying to query all the Events where the users interests match the events interests.
I thought it would look something like this...
#events= Event.find(:all, :conditions => [#user.interests = #event.interests])
but I get the error
"undefined method `interests' for nil:NilClass", Is there something wrong with my syntax or my logic?
You're problem is that either #user or #event is undefined. Even if you define them, before executing this statement, the conditions option supplied is invalid, [#user.interests = #event.interests].
This named scope on events should do the trick
class Event < ActiveRecord::Base
...
named_scope :shares_interest_with_user, lambda {|user|
{ :joins => "LEFT JOIN events_interests ei ON ei.event_id = events.id " +
"LEFT JOIN users_intersets ui ON ui.interest_id = ei.interest_id",
:conditions => ["ui.user_id = ?", user], :group_by => "events.id"
}
end
#events = Event.shares_interest_with_user(#user)
Given Event <-> Interest <-> User query all the Events where the users interests match the events interests (so the following will find all such Events that this event's interest are also interests of at least one user).
First try, the simplest thing that could work:
#events = []
Interest.all.each do |i|
i.events.each do |e|
#events << e if i.users.any?
end
end
#events.uniq!
Highly inefficient, very resource hungry and cpu intensive. Generates lots of sql queries. But gets the job done.
Second try should incorporate some complicated join, but the more I think about it the more I see how vague your problem is. Be more precise.
Not sure I completely follow what you are trying to do. If you have one user and you want all events that that user also has interest in then something like:
Event.find(:all, :include => [:events_interests], :conditions => ['events_interests.interest_id in (?)', #user.interests.collect(&:id)])
should probably work.
In my online store, an order is ready to ship if it in the "authorized" state and doesn't already have any associated shipments. Right now I'm doing this:
class Order < ActiveRecord::Base
has_many :shipments, :dependent => :destroy
def self.ready_to_ship
unshipped_orders = Array.new
Order.all(:conditions => 'state = "authorized"', :include => :shipments).each do |o|
unshipped_orders << o if o.shipments.empty?
end
unshipped_orders
end
end
Is there a better way?
In Rails 3 using AREL
Order.includes('shipments').where(['orders.state = ?', 'authorized']).where('shipments.id IS NULL')
You can also query on the association using the normal find syntax:
Order.find(:all, :include => "shipments", :conditions => ["orders.state = ? AND shipments.id IS NULL", "authorized"])
One option is to put a shipment_count on Order, where it will be automatically updated with the number of shipments you attach to it. Then you just
Order.all(:conditions => [:state => "authorized", :shipment_count => 0])
Alternatively, you can get your hands dirty with some SQL:
Order.find_by_sql("SELECT * FROM
(SELECT orders.*, count(shipments) AS shipment_count FROM orders
LEFT JOIN shipments ON orders.id = shipments.order_id
WHERE orders.status = 'authorized' GROUP BY orders.id)
AS order WHERE shipment_count = 0")
Test that prior to using it, as SQL isn't exactly my bag, but I think it's close to right. I got it to work for similar arrangements of objects on my production DB, which is MySQL.
Note that if you don't have an index on orders.status I'd strongly advise it!
What the query does: the subquery grabs all the order counts for all orders which are in authorized status. The outer query filters that list down to only the ones which have shipment counts equal to zero.
There's probably another way you could do it, a little counterintuitively:
"SELECT DISTINCT orders.* FROM orders
LEFT JOIN shipments ON orders.id = shipments.order_id
WHERE orders.status = 'authorized' AND shipments.id IS NULL"
Grab all orders which are authorized and don't have an entry in the shipments table ;)
This is going to work just fine if you're using Rails 6.1 or newer:
Order.where(state: 'authorized').where.missing(:shipments)