these two scopes don't seem to be chainable
scope :approved, ->{ with_stage(:approved)}
which in sql is
WHERE (pages.stage & 4 <> 0)
and
scope :with_galleries, ->{ joins("LEFT OUTER JOIN galleries ON galleries.galleriable_type = 'Brand' AND galleries.galleriable_id = page.brand_id").where("galleries.id is NOT NULL") }
this scope should give only the pages that have galleries (each page has one brand and each brand can have many galleries)
if I chain the :with_galleries, it seems that the rest of the conditions on pages table is lost
Am I doing the joins wrong?
You would get a more useful result if you let ActiveRecord do more of the heavy lifting for you. In particular, if you've set up associations properly, you should be able to write the following instead:
scope :with_galleries, joins(brand: :galleries)
... which would yield a properly chainable scope.
That would depend on two associations, one from your page model to the brand:
'belongs_to :brand'
and one from the brand to the galleries::
has_many :galleries, as: :galleriable
I'm inferring your model setup from the query that you've written, so I may have guessed wrong. But the basic principle here is to declare your associations and let ActiveRecord construct queries (unless your query is something very unusual, which yours is not -- you're just filtering depending on whether there are associated records, a common operation).
You need to construct the second scope using Arel. The simplest approach is to craft the full SQL statement you want the second scope to represent, and then paste it into http://www.scuttle.io/
Related
I have two models Issue and Label. They have a many to many relationship.
I have a method that returns the ten labels that point to the most issues.
class Label < ApplicationRecord
has_many :tags
has_many :issues, through: :tags
def self.top
Label.joins(:issues)
.group(:name)
.order('count_id desc')
.count(:id)
.take(10)
end
end
It does exactly what I expect it to but I want to know if it's possible to compose the query without the SQL string.
order('count_id DESC') is confusing me. Where does count_id come from? There isn’t a column named count_id.
Label.joins(:issues).group(:name).column_names
#=> ["id", "name", "created_at", "updated_at"]
I’ve found some SQL examples here. I think it’s basically the same as ORDER BY COUNT(Id):
SELECT COUNT(Id), Country
FROM Customer
GROUP BY Country
ORDER BY COUNT(Id) DESC
Is it possible to perform the same query without passing in the SQL string? Can it be done with the ActiveRecord querying interface alone?
If you look at your query log, you'll see something like:
select count(labels.id) as count_id ...
The combination of your group call (with any argument) and the count(:id) call gets ActiveRecord to add the count_id column alias to the query. I don't think this is documented or specified anywhere (at least that I can find) but you can see it happen if you're brave enough to walk through the Active Record source.
In general, if you add a GROUP BY and then count(:x), Active Record will add a count_x alias. There's no column for this so you can't say order(:count_id), order(count_id: :desc), or any of the other common non-String alternatives. AFAIK, you have to use a string but you can wrap it in an Arel.sql to prevent future deprecation issues:
Label.joins(:issues)
.group(:name)
.order(Arel.sql('count_id desc'))
.count(:id)
.take(10)
There's no guarantee about this so if you use it, you should include something in your test suite to catch any problems if the behavior changes in the future.
I feel foolish, but I cannot find the answer to this.
If I have a User with many attributes, given a list of attributes, I can ask rails something like this:
User.where("attributes.id IN ?", list_of_attribute_ids)
With the appropriate joins or includes or whatever.
However, I have no idea how to find the inverse set of those users. That is, given 100 users, if the result return 75 entries, I don't know how to find the other 25!
I thought
User.where("attributes.id NOT IN ?", list_of_attribute_ids)
might work (similarly, User.where.not), but it doesn't! Instead, it looks for those users where any of their attributes are not one of the list, which is useful, but not what I want.
The only way I know how to do it, is with something like:
User.where.not(id: User.where("attributes.id IN ?", list_of_attribute_ids).pluck(:id))
Which is sort of like the SQL for select user where id not in (gather a list of ids).
But this is massively non-performant, and generally just can't cope with a database with more than a few (hundred) entries.
How do you do this?
I think you could use left outer joins, like #Vishal mentioned in the comments.
See the guides: http://guides.rubyonrails.org/active_record_querying.html#left-outer-joins
rails 4:
joins("LEFT OUTER JOIN <something>")
rails 5:
left_outer_joins(:something)
I have a complicated query I need for a scope in my Rails app and have tried a lot of things with no luck. I've resorted to raw SQL via find_by_sql but wondering if any gurus wanted to take a shot. I will simplify the verbiage a bit for clarity, but the problem should be stated accurately.
I have Users. Users own many Records. One of them is marked current (#is_current = true) and the rest are not. Each CoiRecord has many Relationships. Relationships have a value for when they were active (active_when) which takes four values, [1..4].
Values 1 and 2 are considered recent. Values 3 and 4 are not.
The problem was ultimately to have a scopes (has_recent_relationships and has_no_recent_relationships) on User that filters on whether or not they have recent Relationships on current Record. (Old Records are irrelevant for this.) I tried create a recent and not_recent scope on Relationship, and then building the scopes on Record, combining with checking for is_current == 1. Here is where I failed. I have to move on with the app but have no choice but to use raw SQL and continue the app, hoping to revisit this later. I put that on User, the only context I really need it, and set aside the code for the scopes on the other objects.
The SQL that works, that correctly finds the Users who have recent relationships is below. The other just uses "= 0" instead "> 0" in the HAVING clause.
SELECT * FROM users WHERE `users`.`id` IN (
SELECT
records.owner_id
FROM `coi_records`
LEFT OUTER JOIN `relationships` ON `relationships`.`record_id` = `records`.`id`
WHERE `records`.`is_current` = 1
HAVING (
SELECT count(*)
FROM relationships
WHERE ((record_id = records.id) AND ((active_when = 1) OR (active_when = 2)))
) > 0
)
My instincts tell me this is complicated enough that my modeling probably could be redesigned and simplified, but the individual objects are pretty simple, just getting at this specific data from two objects away has become complicated.
Anyway, I'd appreciate any thoughts. I'm not expecting a full solution because, ick. Just thought the masochists among you might find this amusing.
Have you tried using Arel directly and this website?
Just copy-and-pasting your query you get this:
User.select(Arel.star).where(
User.arel_table[:id].in(
Relationship.select(Arel.star.count).where(
Arel::Nodes::Group.new(
Relationship.arel_table[:record_id].eq(Record.arel_table[:id]).and(
Relationship.arel_table[:active_when].eq(1).or(Relationship.arel_table[:active_when].eq(2))
)
)
).joins(
CoiRecord.arel_table.join(Relationship.arel_table, Arel::Nodes::OuterJoin).on(
Relationship.arel_table[:record_id].eq(Record.arel_table[:id])
).join_sources
).ast
)
)
I managed to find a way to create what I needed which returns ActiveRelationship objects, which simplifies a lot of other code. Here's what I came up with. This might not scale well, but this app will probably not end up with so much data that it will be a problem.
I created two scope methods. The second depends on the first to simplify things:
def self.has_recent_relationships
joins(records_owned: :relationships)
.merge(Record.current)
.where("(active_when = 1) OR (active_when = 2)")
.distinct
end
def self.has_no_recent_relationships
users_with_recent_relationships = User.has_recent_relationships.pluck(:id)
if users_with_recent_relationships.length == 0
User.all
else
User.where("id not in (?)", users_with_recent_relationships.to_a)
end
end
The first finds Users with recent relationships by just joining Record, merging with a scope that selects current records (should be only one), and looks for the correct active_when values. Easy enough.
The second method finds Users who DO have recent relationships (using the first method.) If there are none, then all Users are in the set of those with no recent relationships, and I return User.all (this will really never happen in the wild, but in theory it could.) Otherwise I return the inverse of those who do have recent relationships, using the SQL keywords NOT IN and an array. It's this part that could be non-performant if the array gets large, but I'm going with it for the moment.
When I assign a database find to an instance variable in Rails, why do future requests to that variable also hit the database? Can this be avoided?
For example, I have 3 models: User, Resource, Opinion, with has_many :through on Opinion
#opinions = current_user.opinions # pulls in all of the user's opinions, which include respective resource ids
1. Calling for resource_id directly does not hit the database:
#opinions.each do |opinion|
opinion.resource_id # does not hit the database (as expected)
end
2. Performing a query does hit the database (even though variable has been assigned):
#opinions.find_by_resource_id(1) # DOES hit the database
Why does #2 hit the database? Is there a way to perform the same find without hitting the database?
The information is already contained in the #opinions variable, so a db call does not seem necessary.
If you don't need anything else in the #opinions array, I would scope your original query to only include opinions with that resource_id
#opinions = current_user.opinions.where("resource_id = ?", resource_id)
If you already have #opinions and just want to create a new array of objects that match for a specific key/value:
#opinions_with_resource_id = #opinions.select { |opinion| opinion.resource_id == 1234 }
Check out this other answer for another explanation or if you want to split the answer into multiple arrays.
Thoughts
Comment on your last piece of code
Methods like you called find_by_* are dynamic finders that use method_missing to hit the database and look inside of the column specified by the *.
Remaining comments from previous answer
If this object will ever need to access data on the Resource model, don't forget about the #includes() method, which will keep you from having to run additional queries down the road.
#opinions = current_user.opinions.includes(:resources)
See http://guides.rubyonrails.org/active_record_querying.html#eager-loading-associations
Is there a way to get the sql for JUST a scope? So I want to do something like:
class Presentation < ActiveRecord::Base
has_many :calls
has_many :recordings, :through => :calls
scope :with_recordings, joins(:calls).joins(:recordings)
end
And then be able to get the sql for that scope.
Presentations.with_recordings.sql returns the entire sql statement, including the SELECT statement. All I want is the sql added by the scope. Figure there ought to be a way to do this.
I agree with ctcherry about this not being very useful, but having said that, I needed to do this for a project I was working on. We needed to duplicate the sql in the scopes to allow us to reuse the sql across different types of searches. Rather that have to maintain the same sql in two different places, I choose to extract the sql from the scope.
The code below is what I came up with. It's ugly, but works under Rails 3.0
def extract_named_scope_clause(scope, args)
# where_clauses will return an array of clauses for an entire relationship.
# As this is only run a single scope, we only ever care about the first.....
clause, *bind_vars = self.send(scope, args).where_clauses.first
# prefix 'and ' to the string, add some spaces and append any bind variables
if clause
[" and #{clause} ", bind_vars]
else
nil
end
end
This wouldn't really make sense, as there is no standard way to represent SQL "fragments".
The different kinds of SQL "fragments" that can be added and manipulated by a scope don't really have a clean way to be represented by themselves without being part of a complete SQL statement. A fragment could be "JOIN users ON users.id = orders.user_id" or it could be "WHERE active = 1". How would you return these without them being part of a complete SQL statement? This is most likely why there is no mechanism to retrieve them other than the one you have already discovered that just returns the complete SQL statement.