In my RoR application, I've got a database lookup similar to this one:
Client.joins(:products).where({'product.id' => [1,2,3]})
Unfortunately this will return all clients that have bought product 1, 2 or 3 but I only want to get back the clients, that bought all of the three products. In other words, I'd like to write a query that matches for n elements in a given set.
Are there any elegant solutions for this?
This is not really elegant. But it should translate into the needed SQL.
Client.joins(:products).
where({'products.id' => [1,2,3]}).
group('users.id').
having('COUNT(DISTINCT products.id) >= 3')
Same answer with more dynamic way
ids = [1,2,3]
Client.joins(:products).
where({'products.id' => ids}).
group('users.id').
having('COUNT(DISTINCT products.id) >= ?', ids.size)
I have following SQL Query:
SELECT campaigns.* , campaign_countries.points, offers.image
FROM campaigns
JOIN campaign_countries ON campaigns.id = campaign_countries.campaign_id
JOIN countries ON campaign_countries.country_id = countries.id
JOIN offers ON campaigns.offer_id = offers.id
WHERE countries.code = 'US'
This works perfectly well. I want its rails active record version some thing like:
Campaign.includes(campaign_countries: :country).where(countries: {code: "US"})
Above code runs more or less correct query (did not try to include offers table), issue is returned result is collection of Campaign objects so obviously it does not include Points
My tables are:
campaigns --HAS_MANY--< campaign_countries --BELONGS_TO--< countries
campaigns --BELONGS_TO--> offers
Any suggestions to write AR version of this SQL? I don't want to use SQL statement in my code.
I some how got this working without SQL but surely its poor man's solution:
in my controller I have:
campaigns = Campaign.includes(campaign_countries: :country).where(countries: {code: country.to_s})
render :json => campaigns.to_json(:country => country)
in campaign model:
def points_for_country country
CampaignCountry.joins(:campaign, :country).where(countries: {code: country}, campaigns: {id: self.id}).first
end
def as_json options={}
json = {
id: id,
cid: cid,
name: name,
offer: offer,
points_details: options[:country] ? points_for_country(options[:country]) : ""
}
end
and in campaign_countries model:
def as_json options={}
json = {
face_value: face_value,
actual_value: actual_value,
points: points
}
end
Why this is not good solution? because it invokes too many queries:
1. It invokes query when first join is performed to get list of campaigns specific to country
2. For each campaign found in first query it will invoke one more query on campaign_countries table to get Points for that campaign and country.
This is bad, Bad and BAD solution. Any suggestions to improve this?
If You have campaign, You can use campaign.campaign_countries to get associated campaign_countries and just get points from them.
> campaign.campaign_countries.map(&:points)
=> [1,2,3,4,5]
Similarly You will be able to get image from offers relation.
EDIT:
Ok, I guess now I know what's going on. You can use joins with select to get object with attached fields from join tables.
cs = Campaign.joins(campaign_countries: :country).joins(:offers).select('campaigns.*, campaign_countries.points, offers.image').where(countries: {code: "US"})
You can than reference additional fields by their name on Campaign object
cs.first.points
cs.first.image
But be sure, that additional column names do not overlap with some primary table fields or object methods.
EDIT 2:
After some more research I came to conclusion that my first version was actually correct for this case. I will use my own console as example.
> u = User.includes(:orders => :cart).where(:carts => { :id => [5168, 5167] }).first
> u.orders.length # no query is performed
=> 2
> u.orders.count # count query is performed
=> 5
So when You use includes with condition on country, in campaign_countries are stored only campaign_countries that fulfill Your condition.
Try this:
Campaign.joins( [{ :campaign_countries => :countries}, :offers]).where('`countries`.`code` = ?', "US")
Given a table ("Table") as follows (sorry about the CSV style since I don't know how to make it look like a table with the Stack Overflow editor):
id,member,data,start,end
1,001,abc,12/1/2012,12/31/2999
2,001,def,1/1/2009,11/30/2012
3,002,ghi,1/1/2009,12/31/2999
4,003,jkl,1/1/2012,10/31/2012
5,003,mno,8/1/2011,12/31/2011
If using Ruby Sequel, how should I write my query so I will get the following dataset in return.
id,member,data,start,end
1,001,abc,12/1/2012,12/31/2999
3,002,ghi,1/1/2009,12/31/2999
4,003,jkl,1/1/2012,10/31/2012
I get the most current (largest end date value) record for EACH (distinct) member from the original table.
I can get the answer if I convert the table to an Array, but I am looking for a solution in SQL or Ruby Sequel query, if possible. Thank you.
Extra credit: The title of this post is lame...but I can't come up with a good one. Please offer a better title if you have one. Thank you.
The Sequel version of this is a bit scary. The best I can figure out is to use a subselect and, because you need to join the table and the subselect on two columns, a "join block" as described in Querying in Sequel. Here's a modified version of Knut's program above:
require 'csv'
require 'sequel'
# Create Test data
DB = Sequel.sqlite()
DB.create_table(:mytable){
field :id
String :member
String :data
String :start # Treat as string to keep it simple
String :end # Ditto
}
CSV.parse(<<xx
1,"001","abc","2012-12-01","2999-12-31"
2,"001","def","2009-01-01","2012-11-30"
3,"002","ghi","2009-01-01","2999-12-31"
4,"003","jkl","2012-01-01","2012-10-31"
5,"003","mno","2011-08-01","2011-12-31"
xx
).each{|x|
DB[:mytable].insert(*x)
}
# That was all setup, here's the query
ds = DB[:mytable]
result = ds.join(ds.select_group(:member).select_append{max(:end).as(:end)}, :member=>:member) do |j, lj, js|
Sequel.expr(Sequel.qualify(j, :end) => Sequel.qualify(lj, :end))
end
puts result.all
This gives you:
{:id=>1, :member=>"001", :data=>"abc", :start=>"2012-12-01", :end=>"2999-12-31"}
{:id=>3, :member=>"002", :data=>"ghi", :start=>"2009-01-01", :end=>"2999-12-31"}
{:id=>4, :member=>"003", :data=>"jkl", :start=>"2012-01-01", :end=>"2012-10-31"}
In this case it's probably easier to replace the last four lines with straight SQL. Something like:
puts DB[
"SELECT a.* from mytable as a
join (SELECT member, max(end) AS end FROM mytable GROUP BY member) as b
on a.member = b.member and a.end=b.end"].all
Which gives you the same result.
What's the criteria for your result?
If it is the keys 1,3 and 4 you may use DB[:mytable].filter( :id => [1,3,4]) (complete example below)
For more information about filtering with sequel, please refer the sequel documentation, especially Dataset Filtering.
require 'csv'
require 'sequel'
#Create Test data
DB = Sequel.sqlite()
DB.create_table(:mytable){
field :id
field :member
field :data
field :start #should be date, not implemented in example
field :end #should be date, not implemented in example
}
CSV.parse(<<xx
id,member,data,start,end
1,001,abc,12/1/2012,12/31/2999
2,001,def,1/1/2009,11/30/2012
3,002,ghi,1/1/2009,12/31/2999
4,003,jkl,1/1/2012,10/31/2012
5,003,mno,8/1/2011,12/31/2011
xx
).each{|x|
DB[:mytable].insert(*x)
}
#Create Test data - end -
puts DB[:mytable].filter( :id => [1,3,4]).all
In my opinion, you're approaching the problem from the wrong side. ORMs (and Sequel as well) represent a nice, DSL-ish layer above the database, but, underneath, it's all SQL down there. So, I would try to formulate the question and the answer in a way to get SQL query which would return what you need, and then see how it would translate to Sequel's language.
You need to group by member and get the latest record for each member, right?
I'd go with the following idea (roughly):
SELECT t1.*
FROM table t1
LEFT JOIN table t2 ON t1.member = t2.member AND t2.end > t1.end
WHERE t2.id IS NULL
Now you should see how to perform left joins in Sequel, and you'll need to alias tables as well. Shouldn't be that hard.
Sorry to ask all these questions about Kohana. They usually get ignored. I think I just found a bug. I'm making a join between two tables that are not directly related.
$results = ORM::factory('foo')->join("bar")->on("foo.foreign_id", "=", "bar.id");
This generates a query that does not resolve the table names explicitly:
SELECT * FROM `foo` JOIN `bar` ON (`foo`.`foreign_id` = `bar`.`id`)
Which gives (in phpMyAdmin) a table that looks like this:
id time foreign_id blah_int id baz
4 1291851245 3 0 3 52501504
Notice there are two id columns, one for the foo table and one for bar. This is a real problem. Because now, in my results, if I loop through...
foreach ($results as $result) {
echo $result->id; // prints 3!!!
}
Because my results should be foo objects, I expect to get an id of 4, but it's giving me 3 because of the join. Is this a bug in the ORM library? Should I be using a different method to restrict my results from the query? I really don't want to do two separate queries where I load all the bars id's, and then load my foos that way, but it looks like I have to.
You have to use the Database object to build raw queries, not ORM, like this:
$results = DB::select()->from('foo')->join('bar')->on("foo.foreign_id", "=", "bar.id")->execute();
You will need to specific some column aliases however to make your query work unless you use ORM as it was intended.
Using ORM
If you want to use ORM, you need to define the relationships in your model. You mention that they share a relationship with another table so in your case you could use a has many through relationship like this:
protected $_has_many = array(
'bars' => array('model' => 'bar', 'through' => 'other_table', 'foreign_key' => 'foreign_id'),
);
Although your example as given suggests that a straight has_many relationship would work:
protected $_has_many = array(
'bars' => array('model' => 'bar','foreign_key' => 'foreign_id'),
);
This would allow you to access all of the bars using a statement like
$bars = $results->bars->find_all();
foreach($bars as $bar)
{
echo $bar->id; // should echo 4, assuming one record in bars with id 4
}
The Kohana 3.1 ORM Reference Guide is good place to start if you want to learn more about ORM and relationships
Using the Kohana database object and query builder
If you prefer ad hoc queries and are doing joins using the query builder you will likely have colliding column names regardless if you are using Kohana or just raw queries (pop "SELECT * FROM foo JOIN bar ON (foo.foreign_id = bar.id)" into MySQL and you will get the exact same result).
Kohana, just like MySQL allows you to define column aliases for precisely this reason. (See here for more information)
Rewrite your query as follows:
$results = DB::select('id', 'time', 'foreign_id', array('bar.id', 'bar_id'), 'baz')->from('foo')->join("bar")->on("foo.foreign_id", "=", "bar.id")->execute();
This will return:
id time foreign_id blah_int bar_id baz
4 1291851245 3 0 3 52501504
I cant get rails to return combined ('AND') searches on associated join tables of an Object.
E.g. I have Books that are in Categories. Lets say: Book 1: is in category 5 and 8
But I can't get 'AND' to filter results using the join table? E.g ::->
Class Books
has_and_belongs_to_many :categories, :join_table => "book_categories"
Book.find :all, :conditions => "book_categories.category_id = 5 AND book_categories.category_id = 8", :include => "categories"
... returns nil
(why does it not return all books that are in both 5 & 8 ??)
However: 'OR' does work:
Book.find :all, :conditions => "book_categories.category_id = 5 OR book_categories.category_id = 8"
... returns all books in category 5 and 8
I must be missing something?
The problem is at the SQL level. That condition runs on a link table row, and any individual link table row can never have a category_id of both 5 and 8. You really want separate link table rows to have these IDs.
Try looking into Rails' named_scope, specifically the part that allows filtering with a lambda (so you can take an argument). I've never tried it out myself, but if I had to implement what you're looking for, that's what I'd look in to.