ActiveRecord, has_many and _count ...

Discussion in 'Ruby' started by Éric DUMINIL, Aug 28, 2006.

  1. 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])
    @[email protected]
    if @company.update_attributes(params[:company])
    @[email protected]
    @[email protected]:)refresh).size
    @[email protected]:)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. :(


    3) 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
     
    Éric DUMINIL, Aug 28, 2006
    #1
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  2. Éric DUMINIL

    Max Muermann Guest

    I think you want the Rails mailing list...

    Max
     
    Max Muermann, Aug 28, 2006
    #2
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  3. Éric DUMINIL

    zdennis Guest

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    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.

    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
    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.
    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






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    zdennis, Aug 29, 2006
    #3
  4. Éric DUMINIL

    zdennis Guest

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    ^^^^^^^^^^^^^^^
    should be companies_counter. ;)

    Zach
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    zdennis, Aug 29, 2006
    #4
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