Is there any way to get the sql for a single condition or chain of conditions so Booking.where(active: true).to_conditional_sql would return WHERE bookings.active='t' instead of SELECT * FROM bookings WHERE bookings.active='t'
I think you want Scopes:
You can find more about scopes here:
http://guides.rubyonrails.org/active_record_querying.html#scopes
Related
I have a model (News) associated with another model (Category), so in News model i have:
has_and_belong_to_many :news_categories, join:table: 'news_categories_news'
I want to take all news with own categories, so:
News.find(/*conditions*/).includes(:news_categories)
If I check in console I see the right inner join query, but when I call
#news.news_categories
(Where news is a single news in the result array) if I check in console I see another query to take the categories for the current news, how can I avoid this redundant query?
p.s: sorry for my english...
First of all, .includes can't work when chained after .find. Reason - find will not return the ActiveRecord::Relation which is necessary for relational chaining; it will rather return the matching News object or error.
You should do:
#all_news = News.includes(:news_categories).where(id: 1)
#news = #all_news.first
#news.news_categories # shouldn't invoke new query
Thank you to all but i resolved with eager_load()
It's generate just once query!
I am trying to use distinct on in rails with a scope, I've created a method in my model like this:
def self.fetch_most_recent_by_user(scope)
scope.where(guid: scope.except(:select).select("DISTINCT ON (eld_logs.user_id) user_id, eld_logs.guid").order("user_id, eld_logs.created_at desc").map(&:guid))
end
When I execute this I get and error like:
TestModel.fetch_most_recent_by_user(TestModel.includes(:user))
ERROR: syntax error at or near "DISTINCT"
LINE 1: SELECT guid, DISTINCT ON (user_id) user_id...
On searching on DISTINCT ON I found out that it should be the first element in a select statement for postgres to make it work.
I want to prepend the DISTINCT ON in the select statement. I have tried clearing the old select statements using except(:select) which I got from here, but it doesn't work because the includes(:user) prepends users attributes first while doing a left join.
I am using Rails 4.0.13 and Postgres 9.4.12. Any help is appreciated.
I found that if the includes was meddling with the distinct my sub query, because which DISTINCT ON failed. I modified my method to this and it works:
def self.fetch_most_recent_eld_log_by_user(scope, include_associations = { })
scope.where(guid: scope.except(:select).select("DISTINCT ON (eld_logs.user_id) eld_logs.user_id, eld_logs.guid").order("eld_logs.user_id, eld_logs.created_at desc").map(&:guid))
.includes(include_associations)
end
Still it'll be good if someone can provide a way to prepend something in the select statement of active record scope.
First I have this:
has_one :guess
scope :with_guesses, ->{ includes(:guess) }
Which loads all guesses (if they exists) for a 'X' model (run two queries). That's ok. works perfectly.
But I need to add one more condition to It.
If I do (my first thought):
scope :with_guesses, ->(user) { includes(:guess).where("guesses.user_id = ?", user.id) }
It will also run ok, BUT in one query (join) which will exclude results that doesn't have a 'guess'.
Any tips on how to use include with conditions but KEEPING the results that don't have a 'guess' ?
UPDATE
I ended up solving this by using a decorator, which I can pass the user as a context in the controller call, keeping the views clean.
I've used the Draper gem (https://github.com/drapergem/draper) to do this. You don't really need a gem to work with decorators in rails, but it can be helpful.
I didn't test it but you can use something like
User.eager_load(:guesses).where("guesses.user_id = ?", user.id)
when you using includes and where, the includes left join will be inner join.
so if you want to using a left join with where, you have to use string sql fragment:
scope :with_guesses, ->(user) { joins('left outer join guesses on guesses.user_id = ?',
user.id)}
I didn't test this code above, you have to test it yourself, this is just a way to think about
this problem.
here is reference:
http://guides.rubyonrails.org/active_record_querying.html#specifying-conditions-on-eager-loaded-associations
I'd like to change the default statement that ActiveRecord uses to query a model's table. By default, it queries a table "cables" for example by...
this_cable = Cable.first
results in
SELECT "cables".* FROM "cables" LIMIT 1
I would like to find a way for it to wind up with
SELECT *,askml(wkb_geometry) as kml FROM "cables" LIMIT 1
This way i can call a database function and have that behave like a field on the object.
this_cable.kml
=> "<LineString><coordinates>-73.976879999999994,40.674999999999997 -73.977029999999999,40.674779999999998 -73.977170000000001,40.674770000000002 -73.97775,40.67501</coordinates></LineString>"
This can be accomplished by adding a scope
scope :with_kml, "*,askml(wkb_geometry) as kml"
But I figure that's kind of messy. I would like this "kml" column to always be there, without having to call the "with_kml" scope.
Any ideas?
Have you tried using default_scope for this, or do you actually want this to be present on all your models?
Something like this might solve your problem:
default_scope select("*, askml(wkb_geometry) as kml")
You might want to change that to cables.* for it to work properly with joins and such, though.
In Rails 2.3.8 there is a class method ActiveRecord::Base.count_by_sql which allows to perform custom SELECT count(*) .... Is it save to execute customized SELECT sum(...) ... query with this method? If not, what should be done to execute such a query? Is ActiveRecord::Base.connection.execute the only option?
Thanks.
EDIT: Query I want to perform has another query nested. That's why I believe methods from ActiveRecord::Calculations are not sufficient.
Check ActiveRecord::Calculations. The API docs are here.
You can do something like this (assuming you have User model):
User.maximum(:updated_at)
# Generates:
# SELECT max(`users`.updated_at) AS max_updated_at FROM `users`
select_value from ActiveRecord::ConnectionAdapters::DatabaseStatements module is the answer. It returns the value present in the first column of the first row returned by query. select_value returns String, so conversion may be necessary.
Example:
ActiveRecord::Base.connection.select_value("Some complicated sql")