andreibondarev · August 29, 2015 14:16 · Feb 28, 2015
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+# Domain Modeling and Databases
+
+## Learning Objectives
+
+* Describe the basic parts of an ERD
+* Construct ERDs to model the nouns and relationships in a domain
+* Explain what a database is and why you would use one as opposed to other
+  persistent storage mechanisms
+* Explain the difference between a database management system (R/DBMS) and a
+  database, and name the major DBMSes
+* Convert an ERD into a schema and load it into SQLite3
+
+## Framing (5 minutes)
+
+Mention no slides today, but I can provide brief notes / resources if desired.
+
+We've been working with objects for a bit now, and can see some of the benefits.
+**What are those benefits?**
+
+### Think-Pair-Share (30 sec + 2 minutes + 2 minutes)
+
+What problems do we still have working with object? In other words, what's
+missing? What happens when our program quits?
+
+
+While objects and OOP are great, we don't have a way to save our objects, do we?
+
+**What happens when our program quits?**
+
+Even if we could save our objects, how do we 'find' them?
+
+By the end of today, we should have a solution to these problems using
+ActiveRecord, which is a major component of Rails. ActiveRecord uses a database
+to store our objects even when our program quits.
+
+We can use it to create, retrieve, modify, and delete objects.
+
+To get there, we need to talk about four topics:
+* Domain modeling
+* Databases
+* Gems
+* Active Record Basics
+
+
+## Domain Modeling
+
+### Background - What is domain modeling? (5 minutes)
+**I do**
+
+* When talking about a problem, we often think of things in terms of nouns and
+  verbs.
+* The verbs are really methods in our code (so they are 'saved there')
+* The nouns are the objects in our program.
+
+Often what we can do in our code is dictated by what our objects look like and
+how they relate to each other. So it's good practice to think through what
+types objects are in our program, and what attributes they have.
+
+One tool we have for doing this is called an ERD. ERDs only capture the nouns,
+their attributes (instance variables), and their relationships, NOT the verbs.
+
+
+### Class Exercise - Modeling a Library (10 minutes)
+**We do**
+
+Work with students to model a library. List the sorts of nouns that we need to
+include.
+
+As we build the ERD, talk about the concept of relationships (one-one, one-many,
+many-many)
+
+Eg:
+* Books
+* Authors
+* Patrons
+* Shelves
+* Employees
+
+Once we're done, highlight the section of the ERD that we'll be working with for
+today (books and authors).
+
+### Group Exercise - Modeling the class (5 minutes + 10 minutes to present)
+(3 ppl / group)
+**You do**
+
+In groups of 3, choose a problem you're interested in and construct an ERD. Your
+ERD should have at least 3 models, and appropriate relationships and attributes.
+
+Give each group 2 minutes to explain their ERD to the class.
+
+## BREAK (5 minutes)
+
+
+## Intro to Databases
+
+### Background - Why DBs (5 minutes)
+**I DO**
+So we have these ERDs / models for our objects. They only describe the general
+attributes. When we create instances, that's where the actual 'data' is.
+
+We need a way to store that data. How can we do that?
+**Ask class for a few ways to store data**
+
+It turns out that DBs are generally a good solution to solve this problem, why?
+
+* Fast
+* Efficient
+* Very reliable
+* Adaptable
+* Lots of features ('querying', consistency, GIS, etc)
+
+### What is a DB? (10 minutes)
+
+A set of tables, where each table has a structure (columns), and the data
+(rows).
+
+If you've ever used a spreadsheet, DBs are like really advanced spreadsheets.
+
+Demonstrate by drawing the table(s) from the library db on the whiteboard.
+
+### DB Software (5 minutes)
+
+It's important to mention that there are lots of different database tools.
+Common ones include:
+
+* MySQL
+* PostgreSQL
+* SQLite
+* MS SQL Server
+
+Each one has some pros/cons, and features, etc, but they all share something in
+common (SQL - Structured Query Language). These are often called 'Relational DBs'
+
+**Why is the 'relational' important?**
+Consider the R in ERD...
+
+We'll be using SQLite3 because it's easy to set up, but much of what we'll learn
+will transfer to other SQL DBs.
+
+There are other types of DBs that differ in fundamental approach, such as the
+new NoSQL DBs (e.g. MongoDB, Cassandra, Redis)
+
+### Creating a DB (5 minutes)
+
+Demonstrate by creating a simple database, e.g. pokeman:
+
+sqlite3 pokedex
+
+Write the following schema and use Use .read pokemon_schema.sql to read load it in.
+
+```sql
+CREATE TABLE pokemon (
+  id INTEGER PRIMARY KEY,
+  name VARCHAR(255),
+  type VARCHAR(255),
+  hp INTEGER
+);
+```
+
+Describe the different datatypes and why we have to define them in advance.
+Describe the purpose of a primary key and auto-increment.
+
+
+### Group Exercise - Write the schema for Library (10 minutes)
+**YOU DO**
+In groups of 2, create a file folder called `my_library`.
+In that folder create a file called `schema.sql`.
+In that file, create the necessary CREATE statements to create the books and authors
+table from our example.
+
+Provide students with the seed.sql file and have them load it into their DB.
+
+### Wrap Up - Quick demo of SQL (5 minutes)
+
+Frame that we're not going to really be using SQL in this class, instead we'll
+use ActiveRecord to abstract away the DB / SQL.
+
+Demonstrate using SELECT to find records. Demonstrate a JOIN to show how SQL can
+handle relationships.
+
+### BREAK (10 minutes)
+
+Should be 8pm at this point!
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