Count attributes in child model through has_many association

Question

I have two models:

user.rb attributes: name , gender

and

participation.rb attributes: user_id + some other

A user has_many :participations A participation belongs_to :user

I now simply want to find out how many males do I have for a participation collection:

@participations = Participation.all
@males = @participations.joins(:user).where(gender: 'male').count

I understood it this way that I have to join the user model through participations like in the above snippet but that does not work.

Another way would be to simply write:

@males = @participations.users.where(gender: 'male').count

I think I misunderstood something essential here. How can I solve my problem "the rails way"?

Answer 1

您也可以通过:includes使用预先加载：

@males = @participations.includes(:user).where(users: {gender: 'male'})

Answer 2

您应该在查询中指定表名，如下所示：

@males = @participations.joins(:user).where(users: {gender: 'male'})

Answer 3

我将在用户上定义一个男性作用域，然后在您合并该作用域的参与者上定义一个新的关联“ males”或“ male_users”，以使您能够：

@participations.male_users.count