Models based on PostgreSQL views report 'nil' attribute

[tmikoss]

When trying to serialize a ActiveRecord model based on a PostgreSQL view rather than a table, I got a TypeError (nil is not a symbol) exception.

The cause seems to be ActiveRecord reporting additional nil attribute for the model. For example, given a view

CREATE OR REPLACE VIEW example_views AS
SELECT 1 AS id, text 'example' AS name

I get this

irb(main):001:0> ExampleView.first
=> #<ExampleView id: 1, name: "example">
irb(main):002:0> ExampleView.first.attributes
=> {"id"=>1, "name"=>"example", nil=>nil}
irb(main):003:0> ExampleView.column_names
=> ["id", "name"]
irb(main):004:0> ExampleView.first.attribute_names
=> ["id", "name", nil]

Bug observed with Rails 4.1.4 / 4.1.5, PostgreSQL 9.3.5. I've created a minimal Rails application with failing test cases at https://github.com/tmikoss/nil-attribute-in-views

[senny]

I can confirm the issue on 4.1.x. It's fixed on master (4.2.x).

Used this reproduction

[senny]

Upon further investigation I found the cause of this behavior. It's because the model was not able to detect it's primary key. This leads to the nil => nil assignment on this line. Introduced by 522c0fd

You can circumvent the problem by doing:

class ExampleView < ActiveRecord::Base
  self.primary_key = "id"
end

Given that there is an easy workaround and the issue being fixed on master I tend to keep the behavior of 4-1-stable as is.

/cc @rafaelfranca

[tmikoss]

I actually encountered this problem in a view without primary key - it was providing 'flattened' representation of another table:

      CREATE OR REPLACE VIEW item_materials_unnest AS
      SELECT id AS item_id,
             unnest(akeys(manufacturing_materials))::int AS material_id,
             unnest(avals(manufacturing_materials))::int AS material_count
        FROM items

Given item with id: 1, manufacturing_materials: { 2 => 3, 4 => 5 } it would return two rows: item_id: 1, material_id: 2, material_count: 3 and item_id: 1, material_id: 4, material_count: 5.

My workaround was adding

  def attribute_names
    super.compact
  end

to the model. Given that a workaround exists, I'm okay with waiting for next release.

[senny]

@tmikoss I've added test-cases to ensure this will keep working in future versions. Thank you for reporting.

[tmikoss]

Thanks!