Question

I have a table in a legacy database that has a column named field.
It is impossible to link the table directly to an activeRecord model, since the latter will try to create the method field_changed? which is already defined.

So I created a view to rename the field and created the following rules to allow inserts, updates and deletes.

create or replace rule new_linked_fields_upd as on update to new_linked_fields 
     do instead 
     update linked_fields set race_id = new.race_id , master_id = new.master_id, field = new.field_name
     where id = new.id;

create or replace rule new_linked_fields_ins as on insert to new_linked_fields
     do instead
     insert into linked_fields select nextval('linked_fields_id_seq'), new.race_id, new.field_name, new.master_id;

create or replace rule new_linked_fields_del as on delete to new_linked_fields
     do instead
      delete from linked_fields where id = old.id;

I linked the activeRecord model to the view.

class LinkedField < ActiveRecord::Base
  self.table_name ="new_linked_fields"
  self.primary_key = "id"
end

I had to add self.primary_key = “id”, otherwise, methods such as LinkedField.last would fail (generating bad SQL).

In SQL everything works great.
In ruby, I can update the attributes of a LinkedField, or destroy an instance, but I can’t create one.

LinkedField.create(field_name:'toto',race_id:-3,master_id:4)

Returns the following error.

   (0.3ms)  BEGIN
  SQL (1.0ms)  INSERT INTO "new_linked_fields" ("field_name", "master_id", "race_id") VALUES ($1, $2, $3) RETURNING "id"  [["field_name", "toto"], ["master_id", 4], ["race_id", -3]]
   (0.3ms)  ROLLBACK
ActiveRecord::StatementInvalid: PG::Error: ERROR:  syntax error at end of input
LINE 1: DEALLOCATE
                   ^
: INSERT INTO "new_linked_fields" ("field_name", "master_id", "race_id") VALUES ($1, $2, $3) RETURNING "id"
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/postgresql_adapter.rb:297:in `exec'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/postgresql_adapter.rb:297:in `dealloc'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/postgresql_adapter.rb:287:in `delete'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/postgresql_adapter.rb:1172:in `rescue in exec_cache'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/postgresql_adapter.rb:1155:in `exec_cache'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/postgresql_adapter.rb:665:in `block in exec_query'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/abstract_adapter.rb:280:in `block in log'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activesupport-3.2.6/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/abstract_adapter.rb:275:in `log'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/postgresql_adapter.rb:663:in `exec_query'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/abstract/database_statements.rb:63:in `exec_insert'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/abstract/database_statements.rb:90:in `insert'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/abstract/query_cache.rb:14:in `insert'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/relation.rb:66:in `insert'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/persistence.rb:363:in `create'
     from /Users/macbook/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/timestamp.rb:57:in `create'

Any cue? I’m using postgres 9.0 and rails 3.2.6.
Thanks

Answer 1

First, if you’re able to update to PostgreSQL 9.1, view triggers are way easier to get right than rules.

Second, where is DEALLOCATE coming from? Is it trying to free a prepared statement?

Try enabling log_statement = 'all' in postgresql.conf, reloading PostgreSQL (pg_ctl reload, SIGHUP the postmaster, or restart it), re-run your test and examine Pg’s logs. See what SQL your Rails program is actually running.