title: creating tables in ruby-on-rails 3 through migrations?
body: <p>im trying to understand the process of creating tables in ruby-on-rails 3.</p>
  
  <p>i have read about migrations. so i am supposed to create tables by editing in the files in:</p>
  
  <pre><code>Database Migrations/migrate/20100611214419_create_posts
  Database Migrations/migrate/20100611214419_create_categories
  </code></pre>
  
  <p>but they were generated by:</p>
  
  <pre><code>rails generate model Post name:string description:text
  rails generate model Category name:string description:text
  </code></pre>
  
  <p>does this mean i have to use "rails generate model" command everytime i want to create a table?</p>
  
  <p>what if i create a migration file but want to add columns. do i create another migration file for adding those or do i edit the existing migration file directly? the guide told me to add a new one, but here is the part i dont understand. why would i add a new one? cause then the new state will be dependent of 2 migration files.</p>
  
  <p>and how do i add a new migration file for updating then? what is the command? and if i have to drop columns or edit them. how do it do that?</p>
  
  <pre><code>rails generate model Post name:string description:text
  </code></pre>
  
  <p>cause the above command just add columns.</p>
  
  <p>and if i don't use the commands, how do i create migration files?</p>
  
  <p>in symfony i just edit a schema.yml file directly, there are no migration files with versioning and so on.</p>
  
  <p>and i think in django you just create the models and it will create the database tables.</p>
  
  <p>im new to RoR and want to get the picture of creating tables.</p>
  
  <p>thanks</p>