title: 6 simple but fundamental issue in RoR migration for beginner
body: <h2>Hi</h2>
  
  <p>I have 6 simple and fundamental Problem in RoR migration and although I googled it and read many article about it and research it for a week , I didn't understand it. please help me for these problems  :</p>
  
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  <p>1 - When I create a model (for example "rails generate model Football_League") , I see in db/migration a "create_football_leagues.rb" . I want know what is the rules of RoR for changing the name that I gave to my migration ? ( My migration's name was FootballLeague and ruby cretaed "create_football_leagues.rb")</p>
  
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  <p>2 - What is the rules of naming ruby for creating a class in that file ? ( Ruby created a "CreateFootballLeague" class in "create_football_leagues.rb")</p>
  
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  <p>3 - After I use rake db:migrate , although I had 3 migration, I just see below in cmd :
  <img src="https://i.stack.imgur.com/S2BGP.jpg" alt="enter image description here">
  and I didn't any migration for another 3 migrations whereas sometimes ago when I run a migration with rake db:migrate, all my migrations are migrated.</p>
  
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  <p>4 - After I type rake db:migrate and after that Rake execute "create_football_leagues.rb" I go to mysql and I saw a table with "schema_migrations" name. and in that table there are some versions of my migrations. now I want to know what is the application of such a table ?</p>
  
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  <p>5 - In <a href="http://guides.rubyonrails.org" rel="nofollow noreferrer">http://guides.rubyonrails.org</a> I read that if we want to change the primary key of a table from default id to our own field we must use :primary_key option but I didn't understand how can I use it .If someone can give an example for this subject.</p>
  
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  <p>6 - What is the difference between this 2 commands : 1 - "rails generate migration footabll"   2 - rails generate model football. I knew that with "rails generate model football" we must some extra file in app/model  but I don't understand function of those files.</p>
  
  <p>My friend please help me to solve these fundamental problems . special thanks .</p>
  
  <p><strong>* My RoR version is 3.1.3 *</strong></p>