Active_model_serializers: undefined method `model_name' for User::ActiveRecord_Relation:Class

[KevinColemanInc]

edit: this is wrong. see my comment here on how to re-create.

Expected behavior vs actual behavior

I am trying to serialize an ActiveRecord_Relation.

users = User.select('LENGTH(email) as email_length, users.*')
render json: users

class UserSerializer < ActiveModel::Serializer
  attributes :id, :email_length
end

and I get this error message:

undefined method `model_name' for User::ActiveRecord_Relation:Class

this is 0.10.0

[NullVoxPopuli]

what's the output of just users? like if if awesome_printed it?

[bf4]

@KevinColemanInc super important information is missing from this bug report: what did you do to get the error and the stack trace.

undefined methodmodel_name' for User::ActiveRecord_Relation:Class`

what were you doing that caused that issue. We're all busy people https://github.com/rails-api/active_model_serializers/blob/master/.github/ISSUE_TEMPLATE.md#steps-to-reproduce

Thanks

[KevinColemanInc]

@bf4 @NullVoxPopuli Sorry about that! here is a better example:

Steps to reproduce

users = User.select('users.*').joins(:profile).group(:source)

class UserThreeSerializer < ActiveModel::Serializer
  attributes :id
end

ActiveModelSerializers::SerializableResource.new(users, serializer: UserThreeSerializer).to_json

Rendered UserTwoSerializer with ActiveModelSerializers::Adapter::PaginatedJson (4.69ms)
NoMethodError: undefined method `model_name' for User::ActiveRecord_Relation:Class

So it seems like the problem happens when you try to serialize a query that groups the results.

User.all works fine

[KevinColemanInc]

Full backtrace

Rendered UserThreeSerializer with ActiveModelSerializers::Adapter::PaginatedJson (4.75ms)
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model/serializer.rb:175:in json_key' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/adapter/base.rb:51:inroot'
/Users/kcoleman/Sites/steadyfoot/lib/active_model_serializers/adapter/paginated_json.rb:12:in serializable_hash' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/adapter/base.rb:29:inas_json'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/json/encoding.rb:35:in encode' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/json/encoding.rb:22:inencode'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/core_ext/object/json.rb:37:in to_json_with_active_support_encoder' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/serializable_resource.rb:8:into_json'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/logging.rb:69:in block (3 levels) in notify' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:117:incall'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:555:in block (2 levels) in compile' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:505:incall'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:498:in block (2 levels) in around' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:343:inblock (2 levels) in simple'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/logging.rb:22:in block (3 levels) in instrument_rendering' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/logging.rb:79:inblock in notify_render'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/notifications.rb:164:in block in instrument' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/notifications/instrumenter.rb:20:ininstrument'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/notifications.rb:164:in instrument' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/logging.rb:78:innotify_render'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/logging.rb:21:in block (2 levels) in instrument_rendering' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/logging.rb:95:inblock in tag_logger'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/tagged_logging.rb:68:in block in tagged' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/tagged_logging.rb:26:intagged'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/tagged_logging.rb:68:in tagged' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/logging.rb:95:intag_logger'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/logging.rb:20:in block in instrument_rendering' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:441:ininstance_exec'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:441:in block in make_lambda' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:342:inblock in simple'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:497:in block in around' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:505:incall'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:92:in __run_callbacks__' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:778:in_run_render_callbacks'
/Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:81:in run_callbacks' /Users/kcoleman/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.0/lib/active_model_serializers/logging.rb:68:inblock (2 levels) in notify'

[bf4]

Thanks. So, the issue here is that you're serializing a collection (active relation) as if it were a single resource. For collections, you need to specify each_serializer: instead of serializer. I admit these options are a little confusing, but they've been around a while... (in this case, serializer: refers to the collection serializer. It makes sense, but doesn't behave how you'd expect out of the box)

[bf4]

Please let me know if this resolves your issue. If you think the docs or code could be improved with what you've learned, a PR would be most welcome.

[KevinColemanInc]

thanks! I totally forgot about that.

[beauby]

As this issue arises a lot, and custom collection serializers do not seem to be used a lot, it might make sense to have the serializer option handle this automatically when called on a collection.