ActiveRecord Postgres adapter generating invalid SQL WHERE clause: WHERE("fieldname")

Question

ActiveRecord 4.1.1 is generating some peculiar SQL on save that postgres is choking on:

SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
PG::InvalidTextRepresentation: ERROR:  invalid input syntax for type boolean: "uid"

I'm pretty sure that the "boolean" being referred to here is actually the WHERE() syntax which is expecting a boolean expression as an argument.

uid is defined as the primary key on my model (see below)... but why is it just saying WHERE('uid') when it's doing select_all (see stacktrace)? (and why is it doing select_all on save?)

Rails Console

p = Project.new(name: "test", description: "test", workflow_id: 1)
=> #<Project name: "test", description: "test", user_id: nil, uid: nil, created_at: nil, updated_at: nil, workflow_id: 1, active: nil>
irb(main):031:0> p.save
   (1.9ms)  BEGIN
  Project Load (5.5ms)  SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
PG::InvalidTextRepresentation: ERROR:  invalid input syntax for type boolean: "uid"
LINE 1: SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
                                                     ^
: SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
   (1.7ms)  ROLLBACK
ActiveRecord::StatementInvalid: PG::InvalidTextRepresentation: ERROR:  invalid input syntax for type boolean: "uid"
LINE 1: SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
                                                     ^
: SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:815:in `async_exec'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:815:in `block in exec_no_cache'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract_adapter.rb:373:in `block in log'
    from /app/vendor/bundle/ruby/2.0.0/gems/activesupport-4.1.1/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract_adapter.rb:367:in `log'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:815:in `exec_no_cache'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/postgresql/database_statements.rb:137:in `exec_query'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:947:in `select'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/database_statements.rb:31:in `select_all'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/query_cache.rb:69:in `select_all'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/querying.rb:39:in `find_by_sql'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/relation.rb:603:in `exec_queries'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/relation.rb:487:in `load'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/relation.rb:231:in `to_a'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/relation/finder_methods.rb:451:in `find_take'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/relation/finder_methods.rb:98:in `take'
... 41 levels...
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/database_statements.rb:211:in `block in transaction'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/database_statements.rb:219:in `within_new_transaction'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/database_statements.rb:211:in `transaction'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/transactions.rb:208:in `transaction'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/transactions.rb:326:in `with_transaction_returning_status'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/transactions.rb:268:in `block in save'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/transactions.rb:283:in `rollback_active_record_state!'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/transactions.rb:267:in `save'
    from (irb):31
    from /app/vendor/bundle/ruby/2.0.0/gems/railties-4.1.1/lib/rails/commands/console.rb:90:in `start'
    from /app/vendor/bundle/ruby/2.0.0/gems/railties-4.1.1/lib/rails/commands/console.rb:9:in `start'
    from /app/vendor/bundle/ruby/2.0.0/gems/railties-4.1.1/lib/rails/commands/commands_tasks.rb:69:in `console'
    from /app/vendor/bundle/ruby/2.0.0/gems/railties-4.1.1/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
    from /app/vendor/bundle/ruby/2.0.0/gems/railties-4.1.1/lib/rails/commands.rb:17:in `<top (required)>'
    from /app/bin/rails:4:in `require'
    from /app/bin/rails:4:in `<main>

Model

class Project < ActiveRecord::Base

  self.primary_key = "uid"

end

ActiveRecord mixin for generating IDs

module ActiveRecordUIDExtension
  extend ActiveSupport::Concern

    def generate_uid
      return unless self.class.column_names.include?("uid")
      self.id = SecureRandom.random_number(36**10).to_s(36)
      while !self.class.find_by(:uid, self.id).nil? do
       self.id = SecureRandom.random_number(36**10).to_s(36)
      end
  end
end

ActiveRecord::Base.send(:include, ActiveRecordUIDExtension)
ActiveRecord::Base.send(:before_create, :generate_uid)

Gemfile.lock

activerecord (4.1.1)
  activemodel (= 4.1.1)
  activesupport (= 4.1.1)
  arel (~> 5.0.0)

Answer 1

Your mixin doesn't make any sense. This part right here is causing the bad SQL:

self.class.find_by(:uid, self.id)

That's producing invalid SQL because you're telling it to. find_by has a flexible interface so it has to do some parsing to see how you're calling it. When you say:

find_by(a, b)

the argument parsing probably assumes that you're trying to use this form:

find_by('some_sql_snippet', placeholder_valid)

as in this example from the docs:

find_by("published_at < ?", 2.weeks.ago)

Then it will probably to_s the first argument and scan it for placeholders. When you say:

find_by(:uid, self.id)

you'll end up with :uid.to_s and self.id will be ignored because there aren't placeholders in that string. That would explain why you're seeing where ('uid') in the SQL.

Fix your mixin to make sense:

self.class.find_by(:uid => self.id)

or better, switch to exists? to avoid building a whole model instance just to see if there's a row in the database:

self.class.where(:uid => self.id).exists?
self.class.exists?(:uid => self.id)