Wrong SQL for destroy model in Rails 4.2

Question

I have a pretty simlple model:

class SystemKnowledge < ActiveRecord::Base
  validates_presence_of     :system, :value
  validates_numericality_of :value, only_integer: true, greater_than: 0, less_than_or_equal_to: 100

  belongs_to :issue

  attr_accessible :system, :value
end

Once I call model.destroy on an object, I get this error:

ActiveRecord::StatementInvalid: TinyTds::Error: Incorrect syntax near '='.:
EXEC sp_executesql N'DELETE FROM [system_knowledge] WHERE [system_knowledge]. = @0;
SELECT @@ROWCOUNT AS` AffectedRows', N'@0 int', @0 = 275

As far as I get it, the problem is that there is no id field in the generated SQL. What I don't get is why this is happening.

I'm using Rails 4.2 with SQL Express 2014 and TinyTds.

Any help will be greatly appreciated.

Answer 1

Turns out the problem was there was no primary key set up in the DB table. After adding the primary key explicitly to the table, it all began to work.