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###SWABTS Build out a database in a Sinatra project with multiple tables that each connect to a different model.

• MVC - Build model, view and controller for an additional model (Users)
• DATABASES/ACTIVE RECORD - Set up has_many/belongs_to relationships
• ACTIVE RECORD - Understand how has_many/belongs_to works via a user_id column (or similar equivalent for other models)
• ACTIVE RECORD - Build up and down migrations to both create and modify tables
• FORMS - Build a sign up form for new users
• MVC - Create a sign up POST controller that works with the sign up form to create new users
• FORMS - Build forms for something like tweets that connect a tweet object to the user it belongs to
• MVC - Create a layout.erb template and understand how the Ruby keyword yield is used within layout.erb to render partials
• Advanced Students - start thinking about how to create another model to track user's followers or start using ActiveRecord validations?

Last week we did a ton of work with ActiveRecord to get our databases hooked up to our apps. Our twitter database is pretty simple though - we just have one tweets table with users and their statuses. But what if we were keeping track of tweets and followers and trending hashtags and direct messages? We would need a much more complex database with separate tables and models for tweets, users, hashtags and direct messages. Getting all of these tables hooked up to each other and making all of these models play nice is super important and that is where we see the magic of ActiveRecord.

Code snippets can be found here *** Completed Fwitter project for today can be found here

• Why separate tables and models: (tweet model, user model, hashtag model)

  • that breaking up the functionality of an app into smaller pieces makes it easier to scale up and debug applications.
  • Easier to have multiple developers working on different features at the same time
  • Removes the duplication of data - Your user is defined once and then referenced in every tweet that they write.

• Tweet and User Model - making new user model

  • Create a new table. In terminal enter: rake db:create_migration NAME="create_users". Will create new migration
    • In migration (in db directory) create up and down methods.
    • see code snippet 1
    • In terminal: rake db:migrate to create the table
  • Create Users model that maps to that table
    • Create user.rb file in app/models
    • In that file, create a User class that inherits from ActiveRecord::Base
  • Test if you User model and tables are working properly
    • Go into tux and create at least one user

• Adding the V and C

  • Challenge the students to create a new user.erb view and a route in their controller to display that template
  • Encourage them to follow the patterns they used to create MVC for tweets

• Connecting Tweets to Users

  • ActiveRecord makes it easy for us to build relationships between models with two methods called belongs_to and has_many
    • Ask the class - Do you think a user “has_many” tweets or “belongs_to” a tweet?
    • Start mapping out this relationship on the board.
  • So ultimately ActiveRecord will allow us to do something like this:
    • user1.tweets to get an array with all of a user's tweets
    • or tweet1.user to see who created tweet1
  • The first step towards making this connection is to add these methods to the appropriate models
    • See code snippet 2
  • There is one more thing we need to do before this will work - we need to change out Tweets model to include a user_id column
    • The way user1.tweets works is by taking user1's id number and searching through the tweets table for any tweets with a matching user_id column
  • Any time we make a change to our database we need to create a migration with instructions for that change. Here is how you do that:
    • Create a change migration. In terminal enter: rake db:create_migration NAME="modify_tweets".
    • In migration (in db directory) create up and down methods.
    • see code snippet 3
    • In terminal: rake db:migrate to create the table
  • Now that we've modified the tweets table, our current data is no longer valid
  • Go into tux and do Tweet.destroy_all to destroy all of the tweets that are currently in the database
  • Now that we've modified our database we also need to update the info that is being stored in the database
  • Where do we get that input from our users? FORMS

• Modifying the Tweets form

  • Now that we are connecting Tweets to Users via their user id we should probably modify our form to take in user id's instead of user name's
  • Have students update their forms accordingly
  • Create a tweet for user 1
  • Taking in user IDs is not the best way to set up a tweet because users don't always know their ID and if they input the wrong ID our application will error out
    • A much better solution is to create a list of current users that people can choose from
    • We can pull a list of users with User.all and create a drop down menu with that list
    • See code snippet 4

• You guys now have the basic building blocks for setting up databases and applications just like the pros!

• You may need to save the dropdown menu portion of modifying the form for the next class - there is a lot going on in this class
• Emphasize MVC and the need to and modify each portion of the MVC when making updates to the application

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