Saving Data on Android

SQLiteOpenHelper
. 
This will allow the class to utilize the Android SQLite APIs in a simpler way. Your 
class declaration should now look like this:
class
 
ToDoDatabaseHandler
(context: Context) : 
    SQLiteOpenHelper(context, DATABASE_NAME, 
null
, 
DATABASE_VERSION) { 
...
Next up, you have to give the helper the schema data required to build the database.
Crea/ng the database
First, the database must be created if it does not already exist. This is automatically 
done by the 
onCreate
 method, which will run only when it needs to. If the database 
already exists, this method will not run.
Note
: When testing an app that utilizes SQLite, you must uninstall the app to 
delete the old database and reinstall the app to recreate it or completely clear 
the data of an app.
Saving Data on Android
Chapter 3: SQLite Database
raywenderlich.com
53

---

Add the following code to the 
onCreate
 method, in the 
ToDoDatabaseHandler
:
// 1
 
val
 createToDoTable = 
""" 
  CREATE TABLE 
$TABLE_NAME
  ( 
    
$KEY_TODO_ID
 INTEGER PRIMARY KEY, 
    
$KEY_TODO_NAME
  TEXT, 
    
$KEY_TODO_IS_COMPLETED
  LONG ); 
"""
 
// 2
 
db?.execSQL(createToDoTable)
The parts above:
1. Assign an SQL 
Create
 statement which creates the table described in the schema 
above, to the 
createToDoTable
 value.
2. Run the command using the database object provided by the 
SQLiteOpenHelper
.
The above method will be run anytime the app is run and the database is not found. 
Otherwise, the database exists, and there's no reason to recreate it.
One of the downsides of SQL, in general, is having to write the statements perfectly. 
Be very mindful when creating SQL statements using concatenated strings. It is very 
easy to make an error in doing so. It can be helpful to print the query using a 
Log
 
statement to check to see if the string is correct. The text of the query string is also 
displayed at the end of an error message in 
Logcat
 if the app crashes with an error. 
Additionally, you could use a local, or a Web SQL database terminal or environment, 
to try and validate the statement.
Now that the database has been created, you must add a mechanism for upgrading it. 
Add the following code into the 
onUpgrade
 method:
// 1
 
db?.execSQL(
"DROP TABLE IF EXISTS 
$TABLE_NAME
"
) 
// 2
 
onCreate(db)
The above:
1. Executes the SQL statement to drop the old the table if it exists.
2. Calls onCreate again to re-create the database, this time with an upgrade.
Saving Data on Android
Chapter 3: SQLite Database
raywenderlich.com
54

---

The 
onUpgrade
 method is the one that the framework calls automatically when a 
different version of the DB is detected. This happens when an instance of the