# Newbie questions

**URL:** <https://www.ruby-forum.com/t/newbie-questions/180541>\
**Category:** Rails\
**Created:** [December 21, 2009, 2:28pm UTC](https://www.ruby-forum.com/t/newbie-questions/180541 "2009-12-21T14:28:20Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![tutiplain](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/77aa72/32.png) [@tutiplain](https://www.ruby-forum.com/u/tutiplain)\
**Post date:** [December 21, 2009, 2:28pm UTC](https://www.ruby-forum.com/t/newbie-questions/180541/1 "2009-12-21T14:28:20Z")

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Hi all,

I am new to Rails, and I have a few questions about it. I’ve done a  
few tutorials, up to generating a scaffold using SQLite and inserting  
some data.

1. Must I always create my tables using rake db:migrate? Or is it  
possible to create a model using an existing table on an already  
existing database? Can models be made manually?

2. How can I specify table relationships with the generate script? How  
about more complex thing like CASCADE DELETE?

3. I am trying to generate a scaffold using mysql, but I get the  
folowing error when I run db:migrate:

Mysql::Error: query: not connected: CREATE TABLE `schema_migrations`  
(`version`  
varchar(255) NOT NULL) ENGINE=InnoDB

(See full trace by running task with --trace)

I have installed the mysql gem, and my database is properly configured  
in the config/database.yml file. The catalog specified already exists  
on the MySQL server.

---

<div class="post-metadata">

**Author:** ![tutiplain](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/77aa72/32.png) [@tutiplain](https://www.ruby-forum.com/u/tutiplain)\
**Post date:** [December 21, 2009, 3:02pm UTC](https://www.ruby-forum.com/t/newbie-questions/180541/2 "2009-12-21T15:02:49Z")

</div>

tuti plain wrote:

> Hi all,
> 
> I am new to Rails, and I have a few questions about it. I’ve done a  
> few tutorials, up to generating a scaffold using SQLite and inserting  
> some data.
> 
> 1. Must I always create my tables using rake db:migrate? Or is it  
> possible to create a model using an existing table on an already  
> existing database? Can models be made manually?

Models are just ruby classes, so sure you can just make a model.  
However, this is not the approach I would take. Personally, I would not  
create a new Rails application from an existing database (unless there  
was absolutely no other choice).

Chances are that the existing database is not going to be very Rails  
friendly. Instead of using the existing database, I would instead use  
the migrations and build a new database from scratch. I would then  
create scripts to migrate the existing data into the new schema making  
any necessary adjustments to the data to fit a more Rails friendly  
database schema.

> 1. How can I specify table relationships with the generate script? How  
> about more complex thing like CASCADE DELETE?

You don’t do that from generators. Database relations are not really  
something that can be predicted correctly by generators. Fortunately,  
associations in Rails are pretty straight forward and easy to add to  
your model classes.

Rails associations act on the object level. If you want foreign key  
constraints at the database level you need to add those to your database  
migrations.

> 1. I am trying to generate a scaffold using mysql, but I get the  
> folowing error when I run db:migrate:
> 
> Mysql::Error: query: not connected: CREATE TABLE `schema_migrations`  
> (`version`  
> varchar(255) NOT NULL) ENGINE=InnoDB
> 
> (See full trace by running task with --trace)
> 
> I have installed the mysql gem, and my database is properly configured  
> in the config/database.yml file. The catalog specified already exists  
> on the MySQL server.

I don’t know what’s wrong here, but my first suggestions would be to  
build a new empty rails application using MySQL:

rails my\_proj --database mysql

Make sure you’re database.yml is configured correctly for your MySQL  
installation. Then generate a model. Once that’s done run: rake  
db:create. If that succeeds then run: rake db:migrate.

If any of that fails try running with the --trace as suggested in the  
error you listed. Maybe that will point your in the right direction.