How to copy a (Active)record between tables, partially?

Question

In two tables mapped to ActiveRecord with unknown number of identical columns, e.g.:

  Table A      Table B
 ---------    ---------
  id           id
  name         name
  age          email
  email        is_member

How can I (elegantly) copy all identical attributes from a record of Table A to a record of Table B, except the id attribute?

For the example tables above, name and email fields should be copied.

Do you want to write a script that copies the all the records from A just this one time? Or is this something that should happen everytime a new record gets added to A? — Mischa, Sep 16 '10 at 02:05
What constitutes identical columns? is it same name and data type? — Harish Shetty, Sep 16 '10 at 02:54
@KandadaBoggu Same column name. Date type can be assumed identical if column name is identical — ohho, Sep 16 '10 at 03:07

Harish Shetty · Accepted Answer · 2010-09-16T05:09:34.177

7

Try this:

Get intersection of the columns between TableA and TableB

columns = (TableA.column_names & TableB.column_names) - ["id"]

Now iterate through TableA rows and create the TableB rows.

TableB.create( TableA.all(:select => columns.join(",") ).map(&:attributes) )

Edit: Copying one record:

table_a_record = TableA.first(:select => columns.join(","), :conditions => [...])
TableB.create( table_a_record.attributes)

edited Sep 16 '10 at 05:09

answered Sep 16 '10 at 03:19

Harish Shetty

thx. what is the meaning of `.map(&:attributes)`? EDIT: found on http://stackoverflow.com/questions/1217088/what-does-mapname-mean-in-ruby – ohho Sep 16 '10 at 03:43
the current answer will copy all records from `TableA`. How to copy only one record? – ohho Sep 16 '10 at 04:22
1

Updated my answer, take a look. – Harish Shetty Sep 16 '10 at 05:09

score 0 · Answer 2 · answered Sep 16 '10 at 01:58

0

Migt consider using a union function on the acitverecord attributes hash between the 2 tables. It's not a complete answer but may help

answered Sep 16 '10 at 01:58

davydotcom

2 Answers2