Rails - Dec 2005 - help me understand migrations movie

I''m somewhat of a newbie - played with recent versions of rails a few 
mths ago, but have decided to start from scratch with 1.0.
I want to build my new db as much as possible with migrations, so I 
watched DHH''s migrations movie from rubyonrails.org.

A few things confuse me:

1. He generates the model ("post") before running rake db_schema_dump.
Is that necessary or just a preference?

2. He says that running db_schema_dump will create not only the schema 
file, but the database. He''s using sqllite, I''m using MySQL,
and it
didnt work for me. That is, rake db_schema_dump issued an error 
complaining that the database didnt exist.

I created the database in the MySQL console, tried again and it worked.
So question: Does db_schema_dump only create the db for sqllite, or did 
DHH misspeak, or did I misunderstand?

3. DHH then goes into the autogenerated schema.rb and adds code to 
create the tables. He notes the warning about not modifying the 
autogenerated file, but says "we''re going to run with scissors
here".
I appreciate what he''s doing here, but what concerns me is, is this the
way it''s meant to be done? Or is it some shortcut for a quick video?

I''m not criticizing here, I''m just trying to start a project
from
scratch and follow the simplest path.

Is creating the tables in the db console before runing db_schema_dump 
the proper way?
Is db_schema_dump really only meant to be used do dump out the schema 
later?
Should I be creating migrations files to start creating my tables, and 
not be using db_schema_dump first?

Also another startup question: I''m starting my project, and
I''ll be
messing with the table definitions a bit. But I have no data yet and no 
real need for migrations - this is all preliminary stuff - so should I 
create migrations each time for each new column, etc, or "hard code"
it
all in schema.rb, or do it all in the MySQL console.

thanks for any advice offered

-- 
Posted via http://www.ruby-forum.com/.

I would pretty much ignore schema.rb, and just generate new migration 
files, then run "rake migrate" to update your database.

Schema.rb basically is all your migrations in one file, so good for when 
you distribute/deploy an application.

Schema.rb gets created when you run db_schema_dump or gets created 
automatically if you un-comment  "config.active_record.schema_format = 
:ruby" in enviroment.rb.

As far as I am aware you have to create a database first then run rake 
migrate. I guess you could have the database created automatically if 
you add create_database to the first migration file, but I have not 
tried it because some developers may have different database names in 
database.yml depending on their local setup, so there is no need to 
force a database name, only table/field names.

If your messing with tables to start with you could do it without 
migrations using command line or GUI but when you are done do a 
db_schema_dump, and copy the code in schema.rb to your first migration 
file.

I hope that helps...

Kris.

rover rhubarb wrote:
> 
> 1. He generates the model ("post") before running rake
db_schema_dump.
> Is that necessary or just a preference?
> 
> 2. He says that running db_schema_dump will create not only the schema 
> file, but the database. He''s using sqllite, I''m using
MySQL, and it
> didnt work for me. That is, rake db_schema_dump issued an error 
> complaining that the database didnt exist.
> 
> I created the database in the MySQL console, tried again and it worked.
> So question: Does db_schema_dump only create the db for sqllite, or did 
> DHH misspeak, or did I misunderstand?
> 
> 3. DHH then goes into the autogenerated schema.rb and adds code to 
> create the tables. He notes the warning about not modifying the 
> autogenerated file, but says "we''re going to run with
scissors here".
> I appreciate what he''s doing here, but what concerns me is, is
this the
> way it''s meant to be done? Or is it some shortcut for a quick
video?
> 
> I''m not criticizing here, I''m just trying to start a
project from
> scratch and follow the simplest path.
> 
> Is creating the tables in the db console before runing db_schema_dump 
> the proper way?
> Is db_schema_dump really only meant to be used do dump out the schema 
> later?
> Should I be creating migrations files to start creating my tables, and 
> not be using db_schema_dump first?
> 
> Also another startup question: I''m starting my project, and
I''ll be
> messing with the table definitions a bit. But I have no data yet and no 
> real need for migrations - this is all preliminary stuff - so should I 
> create migrations each time for each new column, etc, or "hard
code" it
> all in schema.rb, or do it all in the MySQL console.
> 
> thanks for any advice offered

-- 
Posted via http://www.ruby-forum.com/.

Rover,

If you haven''t already, explore the 2 resources at:
   http://wiki.rubyonrails.com/rails/pages/ActiveRecordMigration

Migrations are brilliant.
When creating a project from scratch, all you have to do on the DB 
server is create an empty DB. Everything - ? - else is done though 
migrations.


I must confess I also found the screencast a little confusing. I watched 
it anyway, and learned a few things.

For example, uncomment this line in ''environment.rb''
  config.active_record.schema_format = :ruby

=> after each migration, ''schema.rb'' will be updated and
show you all
the structures you have created in one place. Invaluable.

There are still a few bugs though.

Alain



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