My environment: Ruby 1.9.2p290, Rails 3.0.9 and RubyGem 1.8.8
unfortunately I have an issue when come across multiple database.
The situation is this: I have two model connect with two different database and also establishing association between each other.
database connection specifying in each model, look likes
class Visit < ActiveRecord::Base
self.establish_connection "lab"
belongs_to :patient
end
class Patient < ActiveRecord::Base
self.establish_connection "main"
has_many :visits
end
I got an error when meet following scenario
#visits = Visit.joins(:patient)
Errors: Mysql2::Error: Table 'lab.patients' doesn't exist: SELECT visits.* FROM visits INNER JOIN patients ON patients.id IS NULL
Here 'patients' table is in 'main' database and 'visits' table in 'lab' database
I doubt when executing the code, that Rails is considering 'patients' table is part of 'lab' database [which holds 'visits' table].
Well, I don't know if this is the most elegant solution, but I did get this to work by defining self.table_name_prefix to explicitly return the database name.
class Visit < ActiveRecord::Base
def self.table_name_prefix
renv = ENV['RAILS_ENV'] || ENV['RACK_ENV']
(renv.empty? ? "lab." : "lab_#{renv}.")
end
self.establish_connection "lab"
belongs_to :patient
end
class Patient < ActiveRecord::Base
def self.table_name_prefix
renv = ENV['RAILS_ENV'] || ENV['RACK_ENV']
(renv.empty? ? "main." : "main_#{renv}.")
end
self.establish_connection "main"
has_many :visits
end
I'm still working through all the details when it comes to specifying the join conditions, but I hope this helps.
Might be cleaner to do something like this:
def self.table_name_prefix
"#{Rails.configuration.database_configuration["#{Rails.env}"]['database']}."
end
That will pull the appropriate database name from your database.yml file
Or even
def self.table_name_prefix
self.connection.current_database+'.'
end
Is your 2nd database on another machine? You can always do as suggested in this other question:
MySQL -- Joins Between Databases On Different Servers Using Python?
I'd use the self.table_name_prefix as proposed by others, but you can define it a little more cleanly like this:
self.table_name_prefix "#{Rails.configuration.database_configuration["#{Rails.env}"]['database']}."
alternatively you could also use this:
self.table_name_prefix "#{connection.current_database}."
You have to keep in mind that the latter will execute a query SELECT DATABASE() as db the first time that class is loaded.
Related
I used rich many to many...
class OwnerRepository < Hanami::Repository
associations do
has_one :avator
has_many :oneships#It's for join table..
has_many :avators,through: :oneships
end
def find_with_avator(id)
aggregate(:avator).where(id: id).map_to(Owner).one
end
def find_with_avators(id)
aggregate(:avators).where(id: id).map_to(Owner).one
#This found one avator but should be found two???
end
end
I create two owners and two avator for each owner,And every owner has two avators with through oneship.
But when i want to find avators with given owner_id,Give me one result.
In other side Avator Repository works fine..
Why?
I'm trying to figure out where to place common functions that I would normally (in Rails/ActiveRecord) put in a model class. Specifically, I have User and Company with a many-to-many relationship between them, but a user has a default_company, which just has a boolean flag on the user_companies join table.
ActiveRecord
class User < ActiveRecord::Base
belongs_to :user_companies
has_many :companies, through: :user_companies
def default_company
# Filter through companies to find the one that I want
end
end
(Note, there's probably an even easier way to do it, but this is the basic idea.)
Ecto
I could do something similar in Ecto, like so:
defmodule MyApp.User do
use MyApp.Web, :model
alias MyApp.{Company, CompaniesUser}
schema "users" do
has_many :companies_users, CompaniesUser, on_delete: :delete_all
many_to_many :companies, Company, join_through: "companies_users"
end
def default_company(%User{} = user) do
from(company in Company,
join: cu in CompaniesUser,
where: cu.company_id == company.id
and cu.user_id == ^user.id
and cu.default_company == true
) |> first() |> Repo.one()
end
end
However, based on my limited experience, this seems incorrect. All the examples I have seen keep the Ecto model very limited, just a bunch of changeset methods and some validation code, but strictly nothing business related. There is talk of keeping your business logic separate from your database logic. I get that and respect it, but most of the examples show putting raw Ecto queries inside a controller or otherwise sprinkling Ecto queries all over your app, and that seems wrong too.
Phoenix 1.3
From what I've read about the upcoming 1.3, it looks like the expectation is that this will be handled with Contexts, or specifically, modules that will allow you to logically group your Ecto schema models along with associated modules that define (manually: you define it) an API to access your persistence layer. So, using my above example, it would be something like:
defmodule MyApp.Account do
alias MyApp.Account.User
alias MyApp.Corporate.{Company, CompaniesUser}
def default_company(%User{} = user) do
from(company in Company,
join: cu in CompaniesUser,
where: cu.company_id == company.id
and cu.user_id == ^user.id
and cu.default_company == true
) |> first() |> Repo.one()
end
end
defmodule MyApp.Account.User do
use MyApp.Web, :model
alias MyApp.Corporate.{Company, CompaniesUser}
schema "users" do
has_many :companies_users, CompaniesUser, on_delete: :delete_all
many_to_many :companies, Company, join_through: "companies_users"
end
end
It has 2 modules, one (MyApp.Account.User) is my raw Ecto schema. The other (MyApp.Account) is the API/entry point for all the other logic in my app, like the controllers.
I guess I like the theory, but I'm worried about trying to figure out what models should go where, like in this example: Does Company belong in the Account context, or do I make a new Corporate context?
(Sorry for asking/answering my own question, but in researching the question I found the info for Phoenix 1.3 and thought I might as well just post for anyone who is interested.)
In my website (written with sinatra) I am trying to set up a database. I have 2 tables, here referred to as Table1 and Table2.
models.rb
class Table1 < ActiveRecord::Base
Table1.where(bool:true) has_one :table2 # PSUDO-CODE
# So that every record where bool:true has the relationship
# but every record where bool:false or bool:nil doesn't
end
class Table2 < ActiveRecord::Base
belongs_to :table1
end
I am trying to find a way to make the section labeled PSUDO-CODE into actual code. How can I do that?
You can't do this directly: a class either has a relationship or it doesn't (although of course there may be no associated record)
You can set conditions on an association, but to the best of my knowledge you can only really set conditions on the associated collection (i.e. table 2 in this case)
You can however override the generated method, so for example
class Table1 < ActiveRecord::Base
has_one :table2
def table2(*args)
bool ? super : nil
end
end
This works with current versions of activerecord - not how far back this is supported (older version defined the association methods directly on the class so you couldn't call super)
I am trying to establish a multiple DB connection with ActiveRecord.Currently I need to insert data into total 2 Databases. There is a possibility for increase in the No.Of databases.
So I created 2 classes dynamically which will Extend from ActiveRecord::Base
Object.const_set("Connection1",Class.new(ActiveRecord::Base) do
self.abstract_class = true
self.establish_connection({
:host=>"localhost", :username=>"root", :password=>"root", :database=>"db1", :encoding=>"utf8", :adapter=>"mysql2"})
end)
Object.const_set("Connection2",Class.new(ActiveRecord::Base) do
self.abstract_class = true
self.establish_connection({
:host=>"localhost", :username=>"root", :password=>"root", :database=>"db2", :encoding=>"utf8", :adapter=>"mysql2"})
end)
Then I created Dynamic models extends from each class accordingly
Object.const_set("ConnectionUser1",Class.new(Connection1) do
self.table_name = 'user'
def self.foo
all.count
end
end)
Object.const_set("ConnectionUser2",Class.new(Connection2) do
self.table_name = 'user'
def self.foo
all.count
end
end)
Then when I tried to call foo method
p ConnectionUser1.foo
p ConnectionUser2.foo
It gives me ActiveRecord::ConnectionNotEstablished Error.
I heard that if the model doesn't have connection ActiveRecord will take connection of their parent.
So according to this ConnectionUser1 should use the connection of Connection1 and ConnectionUser2 use the connection of Connection2.
Then why ActiveRecord fails to Establish Connection?
Any help will be appreciated.
Thank you.
Take a look at below link which shows that how to use multiple database with ActiveRecord.
How do i work with two different databases in rails with active records?
Is there a feature equivalent in MongoMapper to this:
class Model < ActiveRecord::Base
belongs_to :x
scope :with_x, includes(:x)
end
When running Model.with_x, this avoids N queries to X.
Is there a similar feature in MongoMapper?
When it's a belongs_to relationship, you can turn on the identity map and run two queries, once for your main documents and then one for all the associated documents. That's the best you can do since Mongo doesn't support joins.
class Comment
include MongoMapper::Document
belongs_to :user
end
class User
include MongoMapper::Document
plugin MongoMapper::Plugins::IdentityMap
end
#comments = my_post.comments # query 1
users = User.find(#comments.map(&:user_id)) # query 2
#comments.each do |comment|
comment.user.name # user pulled from identity map, no query fired
end
(Mongoid has a syntax for eager loading, but it works basically the same way.)