amng9560 / many_to_many_intro

Many to Many in Ruby

Objectives

1. Define a many to many relationship.
2. Demonstrate building a many to many relationship in Ruby.

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Warmup

1. Come up with some real world examples of a many to many relationship.
2. Try to think of something that connects these two things. Note: the connection between them should be one to many!!!!

What does this look like drawn out?

Let's Do It

Let's use what we know about one to many relationships to create 2 one-to-many relationships.

• Work with your buddy to create a one to many relationship (just one of them).

• We'll create the second one-to-many together.

That's it!!! We've now created a many-to-many relationship.

What can we do with this?

How can we go through our 'join model' to utilize our relationships?

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Deliverables

Slack to me:

1. When using a many-to-many relationship, which model/class holds the information to make the relationship work? In other words, which model knows about the other models?
2. Pretend you have a many to many relationship set up between dogs and parks so the join model is dog_parks. Give an example of how you would instantiate a new dog_park instance.

Getting Practice

You already have your class method .all (Account.all, AccountHolder.all, Bank.all) as well as methods to read all the attributes of instances in those classes. Use those to help you build out the following methods:

1. AccountHolder#accounts

   • Make a method on the account_holder class that returns an array of all accounts that belond to the specific account_holder.

2. AccountHolder#banks

   • Make a method that returns a uniq array of all the bank names an account_holder has.

3. Bank#accounts

   • Method should return all accounts that belong to the specified bank.

4. Bank#account_holders

   • Method should return an array of all account_holders of the specified bank.

5. AccountHolder#new_account(number, nickname, bank)

   • Takes in 3 arguments, the account number, nickname, and bank object and will create a new account associated with the account_holder instance the method was called on.

6. Bank#new_account(number, nickname, account_holder)

   • Takes in 3 arguments, the account number, nickname, and account_holder object and will create a new account associated with the bank instance the method was called on.

7. Bank#oldest_account

   • Method returns the oldest account associated with the specified bank.

8. Bank.most_customers

   • (note the dot instead of the # symbol above. What does that indicate?) Method should return the bank object that has the most customers. *For an extra challenge, have this method also return the number of customers.

9. AccountHolder.average_number_of_accounts

   • Method should return the average number of accounts all account_holders have.

10. Bank.customer_count

    • Method should return a hash where each name of the bank is the key and the values are the number of customers the bank has.

11. Bank#average_customer_age

    • Method should return the average age of all customers for a specific bank.

12. Bank.most_branches

    • Should return the bank with the most number of branches.