SQLite in Android Landon Cox March 2, 2017

What is storage? Storage is persistent Stored state retains its value across launches, reboots Primary interface to storage: files Files can be opened, read, written to, and closed Databases are often implemented on top of files Databases provide a higher-level storage interface (e.g., SQL) Java provides a wealth of ways to interact with storage/files Your code isn’t going to be very useful without storage

Launch Process killed Running Shut down onCreate() onStart() onRestart() onResume() Process killed Running onPause() onStop() onDestroy() Shut down

Saving quiz state Last time: we remembered which quiz we were taking Apps will need to write to storage too Users may expect to pick up where they left off if the app exits What quiz state should you save in case the app exits? Several ways to do this SharedPreferences for simple key-value maps SQLite for more complex kinds of state SharedPreferences Get a reference to SharedPreferences through Context To write: edit, put*, commit To read: get* Last time: we remembered which quiz we were taking

Saving quiz state What else might we want to save? Which quizzes we’ve taken The user’s progress on each quiz The user’s final score on completed quiz How long the user took to complete the quiz Using a key-value store for all of this will become unwieldy Instead: use a relational database like SQLite!

Relational databases Data is organized into tables Tables have named, typed columns Data is stored as rows in a table Can place constraints on columns (e.g., uniqueness) Structure + constraints define the schema Read/write the data base with SQL Structured Query Language (SQL) SQL is declarative It describes what result you want, not how to compute it Example databases: mysql, postgresql, sqlite

SQLite SQLite is the primary database for Android apps Classes for managing your app’s SQLite database Contract class w/ inner BaseColumns class DbHelper class that extends SQLiteOpenHelper Cursor for iterating through answers to queries https://developer.android.com/training/basics/data-storage/databases.html

Define the contract/schema Contract class Place to put all constants related to your database BaseColumns inner class Table names Column names One BaseColumns class for each table in the db _id quiz_title num_correct num_wrong last_question finished_quiz timestamp Duke Basketball 1488460945

Create the database SQLiteOpenHelper class Gives references to SQLiteDatabase instance constructor: super call to create db onCreate: create SQL command to create tables CREATE TABLE quizprogress (_ID INT PRIMARY KEY, quiz_title TEXT, num_correct INT, num_wrong INT, last_question INT, finished_quiz INT, timestamp INT); $> ~/Library/Android/sdk/platform-tools/adb shell $> su $> sqlite3 /data/data/edu.duke.compsci290.quizmaster/databases/

Keywords: create, table Create the database SQLiteOpenHelper class Gives references to SQLiteDatabase instance constructor: super call to create db onCreate: create SQL command to create tables Keywords: create, table CREATE TABLE quizprogress (_ID INT PRIMARY KEY, quiz_title TEXT, num_correct INT, num_wrong INT, last_question INT, finished_quiz INT, timestamp INT);

Table name: quizprogress Create the database SQLiteOpenHelper class Gives references to SQLiteDatabase instance constructor: super call to create db onCreate: create SQL command to create tables Table name: quizprogress CREATE TABLE quizprogress (_ID INT PRIMARY KEY, quiz_title TEXT, num_correct INT, num_wrong INT, last_question INT, finished_quiz INT, timestamp INT);

Create the database SQLiteOpenHelper class Gives references to SQLiteDatabase instance constructor: super call to create db onCreate: create SQL command to create tables Column name: _ID CREATE TABLE quizprogress (_ID INT PRIMARY KEY, quiz_title TEXT, num_correct INT, num_wrong INT, last_question INT, finished_quiz INT, timestamp INT);

Create the database SQLiteOpenHelper class Gives references to SQLiteDatabase instance constructor: super call to create db onCreate: create SQL command to create tables Column type: INT CREATE TABLE quizprogress (_ID INT PRIMARY KEY, quiz_title TEXT, num_correct INT, num_wrong INT, last_question INT, finished_quiz INT, timestamp INT);

Unique to each row: PRIMARY KEY Create the database SQLiteOpenHelper class Gives references to SQLiteDatabase instance constructor: super call to create db onCreate: create SQL command to create tables Unique to each row: PRIMARY KEY CREATE TABLE quizprogress (_ID INT PRIMARY KEY, quiz_title TEXT, num_correct INT, num_wrong INT, last_question INT, finished_quiz INT, timestamp INT);

Column name: quiz_title Create the database SQLiteOpenHelper class Gives references to SQLiteDatabase instance constructor: super call to create db onCreate: create SQL command to create tables Column name: quiz_title CREATE TABLE quizprogress (_ID INT PRIMARY KEY, quiz_title TEXT, num_correct INT, num_wrong INT, last_question INT, finished_quiz INT, timestamp INT);

Create the database SQLiteOpenHelper class Gives references to SQLiteDatabase instance constructor: super call to create db onCreate: create SQL command to create tables Column type: TEXT CREATE TABLE quizprogress (_ID INT PRIMARY KEY, quiz_title TEXT, num_correct INT, num_wrong INT, last_question INT, finished_quiz INT, timestamp INT);

Put information in the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can use insert method INSERT INTO quizprogress (quiz_title, num_correct, num_wrong, last_question, finished_quiz, timestamp) VALUES (“Duke Basketball”, 0, 0, 0, 0, 1488460945) ;

Put information in the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can use insert method Keywords: INSERT, INTO, VALUES INSERT INTO quizprogress (quiz_title, num_correct, num_wrong, last_question, finished_quiz, timestamp) VALUES (“Duke Basketball”, 0, 0, 0, 0, 1488460945) ;

Put information in the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can use insert method List of columns to update INSERT INTO quizprogress (quiz_title, num_correct, num_wrong, last_question, finished_quiz, timestamp) VALUES (“Duke Basketball”, 0, 0, 0, 0, 1488460945) ;

Put information in the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can use insert method INSERT INTO quizprogress (quiz_title, num_correct, num_wrong, last_question, finished_quiz, timestamp) VALUES (“Duke Basketball”, 0, 0, 0, 0, 1488460945) ; Values for each column in new row

Read from the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use query method SELECT _ID, timestamp FROM quizprogress WHERE quiz_title LIKE “Duke Basketball” ORDER BY timestamp DESC;

Keywords: SELECT, FROM, WHERE, LIKE, ORDER BY, DESC Read from the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use query method SELECT _ID, timestamp FROM quizprogress WHERE quiz_title LIKE “Duke Basketball” ORDER BY timestamp DESC; Keywords: SELECT, FROM, WHERE, LIKE, ORDER BY, DESC

Columns in result: _ID, timestamp Read from the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use query method SELECT _ID, timestamp FROM quizprogress WHERE quiz_title LIKE “Duke Basketball” ORDER BY timestamp DESC; Columns in result: _ID, timestamp

Table to query: quizprogress Read from the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use query method SELECT _ID, timestamp FROM quizprogress WHERE quiz_title LIKE “Duke Basketball” ORDER BY timestamp DESC; Table to query: quizprogress

Filter rows using quiz_title Read from the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use query method SELECT _ID, timestamp FROM quizprogress WHERE quiz_title LIKE “Duke Basketball” ORDER BY timestamp DESC; Filter rows using quiz_title

Return results in descending order using timestamp Read from the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use query method SELECT _ID, timestamp FROM quizprogress WHERE quiz_title LIKE “Duke Basketball” ORDER BY timestamp DESC; Return results in descending order using timestamp

Update the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use update method UPDATE quizprogress SET timestamp = 1488460945 WHERE quiz_title LIKE “Duke Basketball”;

Keywords: UPDATE, SET, WHERE, LIKE Update the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use update method UPDATE quizprogress SET timestamp = 1488460945 WHERE quiz_title LIKE “Duke Basketball”; Keywords: UPDATE, SET, WHERE, LIKE

Table to use: quizprogress Update the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use update method Table to use: quizprogress UPDATE quizprogress SET timestamp = 1488460945 WHERE quiz_title LIKE “Duke Basketball”;

New column value: timestamp Update the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use update method New column value: timestamp UPDATE quizprogress SET timestamp = 1488460945 WHERE quiz_title LIKE “Duke Basketball”;

Specify which rows to update Update the database SQLiteDatabase Can submit raw SQL queries w/ execSQL Can also use update method UPDATE quizprogress SET timestamp = 1488460945 WHERE quiz_title LIKE “Duke Basketball”; Specify which rows to update