Rails将关系数据库ID映射到数组中

您可以使用:

@venue.category_ids

试试看: @venue.categories.pluck(:id) .

这将创建 SELECT 仅查询 id 领域

i guess `has_many through` will help you out.for example:-

  #####in user.rb

    ##association for getting all users and thier groups /vice-versa
     has_many :user_groups, :dependent => :destroy
     has_many :groups, :through => :user_groups
 ---------------------------------------------------   
     ####in group.rb

     has_many :user_groups, :dependent => :destroy
     has_many :users, :through => :user_groups
-----------------------------------------------------------     
    #####in user_group.rb

     belongs_to :group
     belongs_to :user
-------------------------------------------------------------    
    ###and we have the necessary migration(its easy... :))..
    so now


    @user=User.find(1)
    all_groups_for_user=@user.groups.where("name=?","Alumni")
    all_names_of_groups_for_user=@user.groups.map(&:name)

如果您使用 scopes/class methods 比您可以使用 joins/include