#5194 ActiveRecord Beta 4 does not understand most postgres data types - Ruby on Rails

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#5194 ✓stale

ActiveRecord Beta 4 does not understand most postgres data types

Reported by Jeff Dean | July 26th, 2010 @ 06:24 AM

I have a postgres database with a table that has a column of type search_vector (and other postgres-specific data geometry data types). Up to Rails 2.3.8 everything was fine, but when I tried upgrading to Rails beta 4 with Arel 0.4.0 I can no longer perform basic queries. The error I get is:

Column type `` is not currently handled

The offending code is in lib/arel/engines/sql/attributes.rb:

module Arel
  module Sql
    module Attributes
      def self.for(column)
        case column.type
        when :string    then String
        when :text      then String
        when :integer   then Integer
        when :float     then Float
        when :decimal   then Decimal
        when :date      then Time
        when :datetime  then Time
        when :timestamp then Time
        when :time      then Time
        when :binary    then String
        when :boolean   then Boolean
        else
          raise NotImplementedError, "Column type `#{column.type}` is not currently handled"
        end
      end
      # ...
    end
  end
end

The column in question looked like this:

#<ActiveRecord::ConnectionAdapters::PostgreSQLColumn:0x34d4a24 @precision=nil, @null=true, @primary=nil, @sql_type="tsvector", @limit=nil, @default=nil, @type=nil, @name="search_vector", @scale=nil>

So there are a few parts to fixing this bug:

fixing the useless error message when it can't understand a column type
making AR use the postgres adapter's column types that were used in previous versions of rails

I'd like to fix this, but before I dig in I'd like some feedback on how. A few things that come to mind are:

Find all places where arel_attributes_values is used and instead call the adapter-specific methods
Create a new Arel Engine for postgres that inherits from the SQL engine, and overrides methods as necessary (then set the correct engine for each connection)
Move all the adapter-specific code to Arel
Making it possible for developers to register their own datatype mapppings without mucking with private apis

If you have an idea what the long-term vision is for making AR work across adapters please let me know. Otherwise, I'll fix this the quickest way I can find and submit a patch. Until then, anybody taking advantage of postgres's other data types is hosed.

Comments and changes to this ticket

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Steve Madsen August 16th, 2010 @ 03:22 AM
This ticket sounds very similar to #4270.

Rails 3.0 RC is unable to save models that make use of Postgres custom data types. Reading is fine; columns with a custom type are treated as String, but writing, even when the custom type column is unchanged, raises the exception reported here.

I made a small change to activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb, around line 119, essentially never delegating type simplification to the superclass. If a specific mapping can't be determined, I always use :string. This fixes my immediate problem, where I don't care about working with the custom type column. (In my case, the custom type is optimized for PostgreSQL indexing and is maintained by a trigger.)

Fixing the ARel issue with the error message looks simple. Instead of complaining about column.type, it should report the column.sql_type.

I'm happy to work up patches for both of these one-liners, but given the stagnation on #4270, I'd like some direction before taking the time to do so.
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Andrea Campi October 17th, 2010 @ 01:24 PM
Can you verify whether this is still an issue after the fix for #5477 has been committed?
Santiago Pastorino February 2nd, 2011 @ 04:29 PM
- State changed from “new” to “open”
This issue has been automatically marked as stale because it has not been commented on for at least three months.

The resources of the Rails core team are limited, and so we are asking for your help. If you can still reproduce this error on the 3-0-stable branch or on master, please reply with all of the information you have about it and add "[state:open]" to your comment. This will reopen the ticket for review. Likewise, if you feel that this is a very important feature for Rails to include, please reply with your explanation so we can consider it.

Thank you for all your contributions, and we hope you will understand this step to focus our efforts where they are most helpful.
Santiago Pastorino February 2nd, 2011 @ 04:29 PM
- State changed from “open” to “stale”
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