database: update exercise 2

Add instructions for how to implement a database abstraction. Add
a template file for the db abstraction. Explain all the methods and
some best practices.

Signed-off-by: soypete <[email protected]>

database/README.md

@@ -31,9 +31,9 @@ Recording to come
 
 ## Exercise 2
 
-Build a client and interface around your database connection.
+Build a client and interface around your database connection. You can use your existing main.go file and build new database package for your abstraction, or you can use the template files found in [database/ex-2-abstraction](database/ex-2-abstraction/main.go). Make sure to create an interface, a User struct, a database client, and the methods to create, update, and query the User data. If you have any questions please put them in the chat.
 
-Questions:
+Follow-up Questions:
 
 * what are the differences between manually creating a database object vs generating one with sqlc?
 

database/ex-2-abstraction/database/database.go

@@ -0,0 +1,49 @@
+package database
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+// Connection struct holds the database connection
+type Connection struct {
+	db *sql.DB
+}
+
+// User struct holds the user data
+type User struct {
+	//TODO: add user fields
+}
+
+type Connector interface {
+	QueryUser() (*User, error)
+	UpdateUser() error
+	AddUser() error
+}
+
+// Connect to database and return a Connection struct.
+// This return value needs to be a pointer because we are
+// using it to implement the Connector interface.
+func Connect() (*Connection, error) {
+	fileName := "database/ex-1-connection/sqlite.db"
+	db, err := sql.Open("sqlite3", fileName)
+	if err != nil {
+		return nil, fmt.Errorf("cannot open sqlite connection: %w", err)
+	}
+	if err = db.Ping(); err != nil {
+		return nil, fmt.Errorf("cannot ping database: %w", err)
+	}
+	return &Connection{db: db}, nil
+}
+
+func (c *Connection) QueryUser() (*User, error) {
+	// TODO: query database
+}
+
+func (c *Connection) UpdateUser() error {
+	// TODO: update database
+}
+
+func (c *Connection) AddUser() error {
+	// TODO: add user to database
+}

database/ex-2-abstraction/main.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"log"
+
+	"github.com/soypete/WebServices-in-3-weeks/database/ex-2-abstraction/database"
+)
+
+func main() {
+
+	// this will enforge the interface
+	var db database.Connector
+	db, err := database.Connect()
+	if err != nil {
+		log.Fatal("Error connecting to database")
+	}
+
+	// call your client methods here
+}