If a Diary has many Pages,
and each Page has many LoveLetters,
and the LoveLetters have many Recipients through Relationships,
then using ActiveRecord, how might I select all Pages who have LoveLetters that have Recipients (through Relationships) of name == "Bob"?
I tried using where, but it makes me specify a foreign key after a certain amount of nested associations, and I can't query the model any more:
diary = Diary.take
diary.pages.where(love_letters: { recipient_id #...
# I can't put 'recipient' here and keep nesting hashes, apparently.
# I think I have to specify the column name.
Not sure if this will work but off the top of my head:
Page.joins(:love_letters).merge(LoveLetter.joins(:recipients)).merge(Recipient.where(:name => "Bob"))
If that doesn't work, try it with Relationships merged also.
Page.joins(:love_letters).merge(LoveLetter.joins(:recipients)).merge(Relationship.merge(:recipients)).merge(Recipient.where(:name => "Bob"))
Related
I'm working on a Rails 3.2 app that uses Datamapper as its ORM. I'm looking for a way to sort a result set by an attribute of the associated model. Specifically I have the following models:
class Vehicle
include DataMapper::Resource
belongs_to :user
end
class User
include DataMapper::Resource
has n, :vehicles
end
Now I want to be able to query the vehicles and sort them by the name of the driver. I tried the following but neither seems to work with Datamapper:
> Vehicle.all( :order => 'users.name' )
ArgumentError: +options[:order]+ entry "users.name" does not map to a property in Vehicle
> Vehicle.all( :order => { :users => 'name' } )
ArgumentError: +options[:order]+ entry [:users, "name"] of an unsupported object Array
Right now I'm using Ruby to sort the result set post-query but obviously that's not helping performance any, also it stops me from further chaining on other scopes.
I spent some more time digging around and finally turned up an old blog which has a solution to this problem. It involves manually building the ordering query in DataMapper.
From: http://rhnh.net/2010/12/01/ordering-by-a-field-in-a-join-model-with-datamapper
def self.ordered_by_vehicle_name direction = :asc
order = DataMapper::Query::Direction.new(vehicle.name, direction)
query = all.query
query.instance_variable_set("#order", [order])
query.instance_variable_set("#links", [relationships['vehicle'].inverse])
all(query)
end
This will let you order by association and still chain on other scopes, e.g.:
User.ordered_by_vehicle_name(:desc).all( :name => 'foo' )
It's a bit hacky but it does what I wanted it to do at least ;)
Note: I'm not familiar with DataMapper and my answer might not be within the standards and recommendations of using DataMapper, but it should hopefully give you the result you're looking for.
I've been looking through various Google searches and the DataMapper documentation and I haven't found a way to "order by assocation attribute". The only solution I have thought of is "raw" SQL.
The query would look like this.
SELECT vehicles.* FROM vehicles
LEFT JOIN users ON vehicles.user_id = users.id
ORDER BY users.name
Unfortunately, from my understanding, when you directly query the database you won't get the Vehicle object, but the data from the database.
From the documentation: http://datamapper.org/docs/find.html. It's near the bottom titled "Talking directly to your data-store"
Note that this will not return Zoo objects, rather the raw data straight from the database
Vehicle.joins(:user).order('users.name').all
or in Rails 2.3,
Vehicle.all(:joins => "inner join users on vehicles.user_id = user.id", :order => 'users.name')
I'm trying to implement search over tags as part of a Texticle search. Since texticle doesn't search over multiple tables from the same model, I ended up creating a new model called PostSearch, following Texticle's suggestion about System-Wide Searching
class PostSearch < ActiveRecord::Base
# We want to reference various models
belongs_to :searchable, :polymorphic => true
# Wish we could eliminate n + 1 query problems,
# but we can't include polymorphic models when
# using scopes to search in Rails 3
# default_scope :include => :searchable
# Search.new('query') to search for 'query'
# across searchable models
def self.new(query)
debugger
query = query.to_s
return [] if query.empty?
self.search(query).map!(&:searchable)
#self.search(query) <-- this works, not sure why I shouldn't use it.
end
# Search records are never modified
def readonly?; true; end
# Our view doesn't have primary keys, so we need
# to be explicit about how to tell different search
# results apart; without this, we can't use :include
# to avoid n + 1 query problems
def hash
id.hash
end
def eql?(result)
id == result.id
end
end
In my Postgres DB I created a view like this:
CREATE VIEW post_searches AS
SELECT posts.id, posts.name, string_agg(tags.name, ', ') AS tags
FROM posts
LEFT JOIN taggings ON taggings.taggable_id = posts.id
LEFT JOIN tags ON taggings.tag_id = tags.id
GROUP BY posts.id;
This allows me to get posts like this:
SELECT * FROM post_searches
id | name | tags
1 Intro introduction, funny, nice
So it seems like that should all be fine. Unfortunately calling
PostSearch.new("funny") returns [nil] (NOT []). Looking through the Texticle source code, it seems like this line in the PostSearch.new
self.search(query).map!(&:searchable)
maps the fields using some sort of searchable_columns method and does it ?incorrectly? and results in a nil.
On a different note, the tags field doesn't get searched in the texticle SQL query unless I cast it from a text type to a varchar type.
So, in summary:
Why does the object get mapped to nil when it is found?
AND
Why does texticle ignore my tags field unless it is varchar?
Texticle maps objects to nil instead of nothing so that you can check for nil? - it's a safeguard against erroring out checking against non-existent items. It might be worth asking tenderlove himself as to exactly why he did it that way.
I'm not completely positive as to why Texticle ignores non-varchars, but it looks like it's a performance safeguard so that Postgres does not do full table scans (under the section Creating Indexes for Super Speed):
You will need to add an index for every text/string column you query against, or else Postgresql will revert to a full table scan instead of using the indexes.
I'm trying to find a record by associated username which is included in a belongs_to relation, but it's not working.
Articles belong to Users
Users have many articles
Article.where(user_id: someid) works fine, but I'd like to use the username as reference which is stored in the Users table.
Article.includes(:user).where(:username => "erebus")
Article.includes(:user).where("user.username" => "erebus")
I also have identity_map_enabled: true
Article.includes(:user).inclusions returns the relation details
Doesn't work, what am I not understanding?
You have to keep in mind that there are no joins in mongodb. In relational dbs, includes forms a join query and you can use columns from both the tables in query. However due to absence of joins in mongodb, same is not possible.
In mongoid, includes just saves a bunch of db calls. It fetches and stores the associated records in identity map for fast retrieval, but still while querying, one query can only deal with one collection.
If you need articles based on user names, I would suggest following work around:
user_ids = User.where(username: 'erebus').only(:_id).map(&:_id)
articles = Article.where(:user_id.in => user_ids)
You can make it little shorter from what rubish suggested:
user_ids = User.where(username: 'erebus').pluck(:id)
articles = Article.where(:user_id.in => user_ids)
Or one liner:
articles = Article.where(:user_id.in => User.where(username: 'erebus').pluck(:id))
I have two models in my rails app with a has many and belongs to association.
Category has many items and Item belongs to category.
These models are associated in the normal way through a category_id column in the Item model.
I'm looking for a quick way of finding all elements in the database with broken associations.
i.e. find all categories that exist with no associated items and items that exist with no associated category.
For example, if I have an item with a category_id of 7, but the category with id 7 has been deleted then this would be considered broken.
For your example, to find items with category_id's for categories which don't exist any more:
Item.where('NOT EXISTS (SELECT * FROM categories where category.id = item.category_id)')
You might want to look at this as well:
A rake task to track down missing database indexes (not foreign keys though, but indexes): https://github.com/eladmeidar/rails_indexes
A very effective way is using find_by_sql to let the database do the heavy lifting:
uncategorized_items = Item.find_by_sql("select * from items where category_id IS NULL")
Another way is a named scope:
class Item < ActiveRecord::Base
scope :uncategorized, where(:category_id => nil) # rails 3
# or...
named_scope :uncategorized, :conditions => 'category_id IS NULL'
end
These are just a couple of ideas. I assume that once you've found these broken associations you plan to fix them, right? You might want to use validates_associated in both models if it's important to you that this not happen again.
You can use find_by_sql and a left outer join to find all the items in one table but not another. Here, I use a downloads table and an image_files table (I've only included the SQL):
SELECT d.*, d.image_file_id
from downloads as d
LEFT OUTER JOIN image_files as i
ON i.id = d.image_file_id
WHERE d.image_file_id IS NULL
Ruby on Rails is very new to me. I am trying to retrieve set of columns from 3 different tables. I thought I could use SQL view to retrieve my results but could not find a way to use views in Rails. Here are my tables.
1) User table --> user name, password and email
2) UserDetails table --> foreign key: user_id, name, address1, city etc.
3) UserWorkDetails --> foreign key: user_id, work address1, work type, etc
These 3 tables have one to one relationships. So table 2 belongs to table 1 and table 3 also belongs to table 1. Table 1 has one userdetails and one userworkdetails.
I want to get user email, name, address1, city, work address1, work type using joins.
What is the best way to handle this?
The data is (are) in the models. Everything else is just an optimization. So address1 is at user.user_detail.address1, for instance.
if you have
class User
has_one :user_detail
has_one :user_work_detail
end
class UserDetail
belongs_to :user
end
class UserWorkDetail
belongs_to :user
end
With user_id columns in tables named user_details and user_work_details then everything else is done for you.
If you later need to optimize you can :include the owned models, but it's not necessary for everything to work.
To get what you want done quickly use the :include option to include both the other tables when you query the primary table, so:
some_user_details = User.find(some_id, :include => [:user_details, :user_work_details])
This will just load all of the fields from the tables at once so there's only one query executed, then you can do what you need with the objects as they will contain all of the user data.
I find that this is simple enough and sufficient, and with this you're not optimising too early before you know where the bottlenecks are.
However if you really want to just load the required fields use the :select option as well on the ActiveRecord::Base find method:
some_user_details = User.find(some_id, :include => [:user_details, :user_work_details], :select => "id, email, name, address1, city, work_address1")
Although my SQL is a bit rusty at the moment.
User.find(:first, :joins => [:user_work_details, :user_details], :conditions => {:id => id})
I'd say that trying to just select the fields you want is a premature optimization at this point, but you could do it in a complicated :select hash.
:include will do 3 selects, 1 on user, one on user_details, and one on user_work_details. It's great for selecting a collection of objects from multiple tables in minimum queries.
http://apidock.com/rails/ActiveRecord/Base/find/class