ERDs
ERDs are diagrams that model the relationships between data.
Car Sales Cars have owners Cars belong to brands Cars have salespeople Sales people have many customers (who have bought a car)
Primary School Teachers have many students Students have one teacher Students have many books
Twitter User has many tweets Tweets has one video
Exercise
Pick one or more of the following analyze what it primarily does & try to draw the tables & relationships. Don't try to model every single piece of data within the app. Start with the most important models and add on from there.
- 99.co
- Github
- Carousell
- AirBnB
- Medium
Hint: If you're not sure how to make a given table or store a piece of data, write in, with dummy data, all the columns of a single record / row.
1
An ERD diagram, using crow's foot notation, of whatever app you choose. For example:
Note: this example has "Items" as placeholders for the attributes.
Warning: DO NOT try to implement the entire app. That will be way too big. Start with the major features. Then move on to the next part (2). If you get done with the below, come back and add to the ERD.
2
Write the tables.sql file for this app.
(If you found out you made a mistake in your table creation when you run your seed file, or when you are working on your own at all, make sure to coordinate with your partner to fix these errors.)
3
Write a seed.sql for the first row or two in every table.
4
Write the sql SELECT queries that gets every major relationship in the app in a queries.sql file. (Make sure you have enough dummy data to get at least one row.)
For example, for Facebook, write an sql SELECT to get:
- my friends on Facebook
- photos I'm tagged in
- every user in a Facebook group
- etc.