# ActiveRecord, has\_many and \_count **URL:** \ **Category:** Ruby\ **Created:** [August 28, 2006, 10:28pm UTC](https://www.ruby-forum.com/t/activerecord-has-many-and-count/66736 "2006-08-28T22:28:26Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![SSSSric\_DUMINIL](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/3da27b/32.png) [@SSSSric\_DUMINIL](https://www.ruby-forum.com/u/SSSSric_DUMINIL)\ **Post date:** [August 28, 2006, 10:28pm UTC](https://www.ruby-forum.com/t/activerecord-has-many-and-count/66736/1 "2006-08-28T22:28:26Z")
Hi everybody! Here are trunks of models from a little rails app I’m developing: ########################### class Country \< ActiveRecord::Base has\_many :companies … ########################### class Category \< ActiveRecord::Base has\_many :companies … ########################### class Company \< ActiveRecord::Base has\_many :employees , :dependent =\> true belongs\_to :country, :counter\_cache =\> true belongs\_to :category, :counter\_cache =\> true … ########################### class Employee \< ActiveRecord::Base belongs\_to :company, :counter\_cache =\> true … ########################### I just would like to know: The right way to create a new company by updating Country.find(id).companies.size is by doing Country.find(id).companies.create . Right? 1. But what if I’d like to keep in cache companies.size for the category in which the new company is put? I can’t create a company simultaneously using two parents! 2. When I edit the properties of a company, let’s say moving from Japan to Italy, how could I update Japan.companies\_count and Italy.companies\_count? I tried to modify the update action of CompanieController: ########################### def update @company = Company.find(params[:id]) @oldcountry=@company.country if @company.update\_attributes(params[:company]) @newcountry=@company.country @oldcountry.companies\_count=@oldcountry.companies(:refresh).size @newcountry.companies\_count=@newcountry.companies(:refresh).size flash[:notice] = ‘Company was successfully updated.’ redirect\_to :action =\> ‘show’, :id =\> @company else render :action =\> ‘edit’ end end ########################### but that did’nt work. ☹ 1. Is there a Rails’ way to cache the number of Employees directly in Company.employees\_count and Category.employees\_count (i.e. through a “has\_many\_many” relation)? That would prevent iterating through every company of a given country/category to get its .employees\_count! Thanks a lot for your attention, Have a good night, Eric ---
**Author:** ![SSSSric\_DUMINIL](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/3da27b/32.png) [@SSSSric\_DUMINIL](https://www.ruby-forum.com/u/SSSSric_DUMINIL)\ **Post date:** [August 29, 2006, 12:15am UTC](https://www.ruby-forum.com/t/activerecord-has-many-and-count/66736/2 "2006-08-29T00:15:02Z")
I think you want the Rails mailing list… Max ---
**Author:** ![SSSSric\_DUMINIL](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/3da27b/32.png) [@SSSSric\_DUMINIL](https://www.ruby-forum.com/u/SSSSric_DUMINIL)\ **Post date:** [August 29, 2006, 4:29am UTC](https://www.ruby-forum.com/t/activerecord-has-many-and-count/66736/3 "2006-08-29T04:29:29Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Éric DUMINIL wrote: > I just would like to know: The right way to create a new company by updating > Country.find(id).companies.size is by doing > Country.find(id).companies.create . Right? This is one way of doing it. Although if you have the id of the Country you can just say: company = Company.create( :company\_name=\>‘ABC Co’, :country\_id=\>1 ) OR company = Company.new( :company\_name=\>‘ABC Co’, :country\_id=\>1 ) company.save Both of these will update the country countries\_counter because you have defined this in your belongs\_to relationship. > 1. But what if I’d like to keep in cache companies.size for the category in > which the new company is put? I can’t create a company simultaneously using > two parents! This can be solved using create or save on Company itself, rather then doing Country.find.companies.create. Since you have defined the belongs\_to relationship and specified the counter cache ActiveRecord will be smart enough to update both of them. The following example will work: Company.create :company\_name=\>‘ABC’, :country\_id=\>1, :category\_id=\>1 > 1. When I edit the properties of a company, let’s say moving from Japan to > Italy, how could I update Japan.companies\_count and Italy.companies\_count? If you edit the properties of a company and save it ActiveRecord will correctly increment/decrement the counter cache fields that you have placed on your tables. Using :refresh will ensure that you get the most recent data from the database. > 1. Is there a Rails’ way to cache the number of Employees directly in > Company.employees\_count and Category.employees\_count (i.e. through > a “has\_many\_many” relation)? That would prevent iterating through every > company of a given country/category to get its .employees\_count! I don’t know about the count via a another relationship, but you can always count them at once rather then iterating over each company. Category.count( :joins=\>"INNER JOIN #{Company.table\_name} ON " + “#{Company.table\_name}.category\_id=” + “#{Category.table\_name}.id " + “INNER JOIN #{Employee.table\_name} ON " + “#{Employee.table\_name}.company\_id=#{Company.table\_name}.id”, :group=\>”#{Category.table\_name}.id” ) This will give you an array of arrays, where each internal array is employee\_count, category\_id: [[ 4, 1], [2, 2], [30, 3] ] It doesn’t handle categories that do not have any employees although that could be fixed. This is perhaps not as simple of a solution you’re looking for. Perhaps someone else knows if you can do counter\_cache using :through. 😉 Zach -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2.2 (GNU/Linux) Comment: Using GnuPG with Mozilla - [http://enigmail.mozdev.org](http://enigmail.mozdev.org) iD8DBQFE86bfMyx0fW1d8G0RAukPAJ9h4COcF11Zrzo0AVqjV1t8Il1hjACfcbuQ 7Qqh6h2BI4zt9P8WjMq59cg= =Nz8h -----END PGP SIGNATURE----- ---
**Author:** ![SSSSric\_DUMINIL](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/3da27b/32.png) [@SSSSric\_DUMINIL](https://www.ruby-forum.com/u/SSSSric_DUMINIL)\ **Post date:** [August 29, 2006, 4:35am UTC](https://www.ruby-forum.com/t/activerecord-has-many-and-count/66736/4 "2006-08-29T04:35:29Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 zdennis wrote: > This is one way of doing it. Although if you have the id of the Country > you can just say: > company = Company.create( :company\_name=\>‘ABC Co’, :country\_id=\>1 ) > OR > company = Company.new( :company\_name=\>‘ABC Co’, :country\_id=\>1 ) > company.save > > Both of these will update the country countries\_counter because you have > ^^^^^^^^^^^^^^^ > should be companies\_counter. 😉 Zach -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2.2 (GNU/Linux) Comment: Using GnuPG with Mozilla - [http://enigmail.mozdev.org](http://enigmail.mozdev.org) iD8DBQFE86hbMyx0fW1d8G0RAsWHAJ0XsQqlFXZePu0A+xXdsw3FRn4DfQCfUAyX xNpxNiX3RqhDAfutQC3Ud1k= =P1Yo -----END PGP SIGNATURE-----