I need to convert a legacy database - the usual non-Railish schema with several million rows - to a Rails-compatible schema. Are there any tools / tutorials / books / blog-posts that would help me with that? I need to solve problems like connecting to two databases at the same time, querying the old non-Railish schema and using the data to create Rails objects, etc. Thanks in advance, Maurice B. Gladwell A recent Rails convert
on 2007-05-30 14:17
on 2007-05-30 14:36
Maurice, Which DBMS ? Each DBMS has different facilities available and different capabilities, especially when it comes to linking two databases together. If you are migrating everything, you'd probably be a lot easier putting it all into one database which will save you have to use "federated" support to join across databases. You also have a chance to think whether you want to change DBMS. Are you talking about modifying the structures ? If so, the book "Refactoring Databases : Evolutionary Database Design" by Scott Ambler and Pramodkumar J Sadalage (Addison-Wesley, ISBN-10: 0321293533, ISBN-13: 978-0321293534) is a great primer for the types of changes you will have to make. The biggest challenge you are going to face is making modifications while not breaking existing applications (I assume you have existing apps). If I can be any help then drop me a line : especially if you wish to consider DB2 as the DBMS of choice going forward. DB2 has good Rails support, and getting better by the day, and the free DB2 Express-C has no limit on database size, only on memory (4 gig) and processors (2 sockets, not cores). HTH Phil (email@example.com)
on 2007-05-30 14:42
The Rails recipes from the Pragmatic Programmers by Chad Flower, has some tips on connecting to legacy databases. That should point you in the right direction, or at least give you some idea of what you're up against
on 2007-05-30 15:17
Hi Phil, The DBMS is MySQL 5. It is serving a single, high-traffic web application. My naive approach was much simpler than what you outlined - I was thinking about writing a conversion script, that will: 1) go over the legacy database, pulling data from it 2) use data pulled in #1 to instantiate ActiveRecord objects, which will be compatible with the new schema of the new database 3) save those ActiveRecord objects to the new database Does that make sense? I thought it would be the most conventional approach, so there must be material describing such a procedure. -- M.
on 2007-05-30 15:18
You might also want to look at the ETL (Extract, Transform, Load) approach found in active_warehouse. If you can reduce your dependency to cyclical connectivity (say daily or hourly), you can simplify the process quite a bit. Or, if you could ETL the legacy data and just maintain connectivity for the sake of a few tables, you've reduced the runtime load and complexity of your system quite a bit.
on 2007-05-31 11:36
Hi Maurice, On May 30, 2:17 pm, Maurice Gladwell <rails-mailing-l...@andreas- s.net> wrote: > Does that make sense? I thought it would be the most conventional > approach, so there must be material describing such a procedure. This is exactly how we're doing it for one of our clients. We've created AR objects for all the old tables, and then we're doing a find on the old AR object, and looping over the result, to stick it into the new AR models. Something like this: --- class ImportBibData < ActiveRecord::Base establish_connection :import set_table_name "BibData" end --- Then doing something like this... --- i_bib_items = ImportBibItem.find_all_by_doctype("M") i_bib_items.each do |i_bib_item| new_object = NewObject.find_or_create_by_import_id(i_bib_item.bibid) end ---- It's not DRY at all, and it's quite a bit of a mess - but it's going to be more or less a one-off import once the client freezes their old (Access!!) DB and we start the import. Hope that's of any help. Cheers, JS PS, my first post, so have mercy with me if I'm doing something wrong! PPS, Hi all!
on 2007-05-31 12:58
How are you connecting to Access? I hope this isn't too OT, but there are a lot of threads in this and other forums saying it's a mess/not worth it. Ron
on 2007-05-31 14:28
Re connecting to multiple databases. Bookmarked this 'how to' earlier today anticipating a similar need: http://www.railsonwave.com/railsonwave/2006/12/11/... On May 30, 8:17 am, Maurice Gladwell <rails-mailing-l...@andreas-
on 2007-06-01 10:35
On May 31, 11:57 am, paron <rphill...@engineer.co.summit.oh.us> wrote: > How are you connecting to Access? I hope this isn't too OT, but there > are a lot of threads in this and other forums saying it's a mess/not > worth it. It is a mess - so we don't! :D We use the mdb-tools package to extract the data as CSV, and the schema as SQL. We then convert the schema to MySQL compatible SQL, and dump it into MySQL. From there we run a mysqlimport on the CSV files to populate the DB with the old data. It's a mess for sure, but once it's in the MySQL DB it's much nicer to work with, and once it's in the new structure we should be all happy smiling Railers... /Jocke