在“has_many”“through”关联上使用“find_or_create_by”时出错
我在 has_many through 关联上使用 find_or_create_by 时遇到问题。
class Permission < ActiveRecord::Base
belongs_to :user
belongs_to :role
end
class Role < ActiveRecord::Base
# DB columns: user_id, role_id
has_many :permissions
has_many :users, :through => :permissions
end
class User
has_many :permissions
has_many :roles, :through => :permissions
end
当我对 User 对象的 roles 关联调用 find_or_create_by 时，Rails 会引发错误。
u = User.first
u.roles.find_or_create_by_rolename("admin")
# Rails throws the following error
# NoMethodError: undefined method `user_id=' for #<Role id: nil, rolename: nil,
# created_at: nil, updated_at: nil>
我能够通过更改代码来解决该问题，如下所示：
unless u.roles.exists?(:rolename => "admin")
u.roles << Role.find_or_create_by_rolename("admin")
end
我很好奇 find_or_create_by 是否可以与 has_many through 关联一起使用。
I am running in to a problem while using find_or_create_by on a has_many through association.
class Permission < ActiveRecord::Base
belongs_to :user
belongs_to :role
end
class Role < ActiveRecord::Base
# DB columns: user_id, role_id
has_many :permissions
has_many :users, :through => :permissions
end
class User
has_many :permissions
has_many :roles, :through => :permissions
end
Rails throws an error when I invoke find_or_create_by on roles association of a User object.
u = User.first
u.roles.find_or_create_by_rolename("admin")
# Rails throws the following error
# NoMethodError: undefined method `user_id=' for #<Role id: nil, rolename: nil,
# created_at: nil, updated_at: nil>
I was able to work around the problem by changing my code as follows:
unless u.roles.exists?(:rolename => "admin")
u.roles << Role.find_or_create_by_rolename("admin")
end
I am curious to find if find_or_create_by works with has_many through associations.
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它可以工作，但不能与
:through一起使用。It works, but not with
:through.