07. Data Storage

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1 07. Data Storage

2 Agenda Data storage options How to store data in key-value pairs How to store structured data in a relational database 2

3 Data Storage Options Shared Preferences Store private primitive data in key-value pairs. Internal Storage Store private data on the device memory. External Storage Store public data on the shared external storage. SQLite Databases Store structured data in a private database. Network Connection Store data on the web with your own network server. 3

4 SQL 4

5 Introduction to SQL SQL stands for Structured Query Language SQL is a computer language for storing manipulating retrieving data stored in relational database SQL Commands Data Definition Language (DDL) CREATE, ALTER, DROP Data Manipulation Language (DML) SELECT, INSERT, UPDATE, DELETE Data Control Language (DCL) GRANT, REVOKE 5

6 Create Table The CREATE TABLE statement is used to create a table in a database CREATE TABLE table_name ( column1 datatype, ); column2 datatype CREATE TABLE tblemployee( ID INT department VARCHAR(20), salary DECIMAL(18,2) ); 6

7 Drop Table The DROP TABLE statement is used to delete a table DROP TABLE table_name; DROP TABLE tblemployee; 7

8 Select Data From Table The SELECT statement is used to select data from a database SELECT column1, column2...columnn FROM table_name; WHERE conditions GROUP BY column1, column2 HAVING conditions ORDER BY column1{asc DESC} 8

9 Select Example 1 ID Department Salary 100 HR IT HR IT 1400 SELECT ID, department FROM tblemployee WHERE ID=101; ID Department 101 IT 9

10 Select Example 2 ID Department Salary 100 HR IT HR IT 1400 SELECT ID, salary FROM tblemployee WHERE Department=IT ORDER BY DESC; ID Salary

11 Select Example 3 ID Department Salary 100 HR IT HR IT 1400 SELECT department, sum(salary) FROM tblemployee GROUP BY department; Department Salary HR 2250 IT

12 Select Example 4 ID Department Salary 100 HR IT HR IT 1400 SELECT department, sum(salary) FROM tblemployee GROUP BY department HAVING sum(salary)>2500; Department Salary IT

13 Insert Data The INSERT INTO statement is used to insert new records in a table INSERT INTO table_name (column1, column2,...columnn) VALUES (value1, value2,...valuen) Example INSERT INTO tblemployee (ID, department,salary) VALUES (105, IT, 1400) 13

14 Update Data The UPDATE statement is used to update records in a table UPDATE table_name SET column1=value1, column2=value2 WHERE condition Example UPDATE tblemployee SET salary=2000 WHERE ID=101 14

15 Delete Data The DELETE statement is used to delete records in a table DELETE FROM table_name WHERE condition Example DELETE FROM tblemployee WHERE ID=101 15

16 SQLite 16

17 What is SQLite? SQLite is a open source SQL database that stores data to a text file on a device Android comes in with built in SQLite database implementation SQLite supports all the relational database features like SQL syntax, transactions and prepared statements 17

18 SQLite Data Types NULL The value is a NULL value. INTEGER The value is a signed integer, stored in 1, 2, 3, 4, 6, or 8 bytes depending on the magnitude of the value. REAL The value is a floating point value, stored as an 8-byte IEEE floating point number. TEXT The value is a text string, stored using the database encoding (UTF-8, UTF-16BE or UTF-16LE). BLOB The value is a blob of data, stored exactly as it was input 18

19 SQLite in Android SQLite is embedded into every Android device. Using an SQLite database in Android does not require a setup procedure or administration of the database. You only have to define the SQL statements for creating and updating the database. Afterwards the database is automatically managed for you by the Android platform. The database is by default saved in the directory DATA/data/APP_NAME/databases/FILENAME. 19

20 SQLite in Android The android.database package contains all necessary classes for working with databases. The android.database.sqlite package contains the SQLite specific classes. To create and upgrade a database in your Android application you create a subclass of the SQLiteOpenHelper class 20

21 SQLiteOpenHelper A helper class to manage database creation and version management You create a subclass implementing oncreate(sqlitedatabase) Called when the database is created for the first time onupgrade(sqlitedatabase, int, int) Called when the database needs to be upgraded 21

22 SQLiteOpenHelper public class DatabaseHandler extends SQLiteOpenHelper { /* Constructor */ public DatabaseHandler(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } /* Create table on public void oncreate(sqlitedatabase db) { } /* Update table on public void onupgrade(sqlitedatabase db, int oldversion, int newversion) { } } 22

23 SQLiteOpenHelper Parameters context name factory to use to open or create the database name of the database file, or null for an in-memory database to use for creafng cursor objects, or null for the default version - number of the database (starfng at 1) - if the database is older, onupgrade(sqlitedatabase, int, int) will be used to upgrade the database - if the database is newer, ondowngrade(sqlitedatabase, int, int) will be used to downgrade the database 23

24 Create and Upgrade Table public class DatabaseHandler extends SQLiteOpenHelper { private static final int DATABASE_VERSION = 1; //-- Database Version private static final String DATABASE_NAME = "contactsdb ; //-- Database Name private static final String TABLE_CONTACTS = "tblcontacts ; //-- Contacts table name private static final String COL_KEY_ID = "id ; //-- ID Column private static final String COL_NAME = "name"; //-- Name Column private static final String COL_PHONE = "phonenumber ; //-- Phone Column public DatabaseHandler(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); public void oncreate(sqlitedatabase db) { String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "(" + COL_KEY_ID + " INTEGER PRIMARY KEY," + COL_NAME + " TEXT," + COL_PHONE + " TEXT" + ")"; db.execsql(create_contacts_table); public void onupgrade(sqlitedatabase db, int oldversion, int newversion) { //-- drop older table if existed db.execsql("drop TABLE IF EXISTS " + TABLE_CONTACTS); //-- create tables again oncreate(db); } 24

25 SQLiteOpenHelper Methods SQLiteDatabase getreadabledatabase() Create and/or open a database for read Returns a database object valid until getwritabledatabase() or close() is called. SQLiteDatabase getwritabledatabase() Create and/or open a database that will be used for reading and writing Returns a read/write database object valid until close() is called 25

26 SQLiteDatabase Exposes methods to manage a SQLite database. SQLiteDatabase has methods to create delete execute SQL commands perform other common database management tasks. 26

27 void execsql () Execute a single SQL statement that is NOT a SELECT or any other SQL statement that returns data. Parameters sql the SQL statement to be executed. MulFple statements separated by semicolons are not supported 27

28 Cursor rawquery () Runs the provided SQL and returns a Cursor over the result set. Parameters sql the SQL query selecfonargs You may include?s in where clause in the query, which will be replaced by the values from selecfonargs Return A Cursor object, which is posifoned before the first entry 28

29 rawquery Example public List<Contact> getallcontacts() { SQLiteDatabase db = this.getwritabledatabase(); List<Contact> contactlist = new ArrayList<Contact>(); String selectquery = "SELECT * FROM " + TABLE_CONTACTS; //-- select all query //-- run query on db Cursor cursor = db.rawquery( selectquery, // the SQL query. null); } //-- loop through all rows and adding to list if (cursor.movetofirst()) { //-- Move the cursor to the first row do { Contact contact = new Contact(); contact.setid(cursor.getint(0)); contact.setname(cursor.getstring(1)); contact.setphonenumber(cursor.getstring(2)); } contactlist.add(contact); //-- add contact to list } while (cursor.movetonext()); // Move the cursor to the next row //-- close resources cursor.close(); db.close(); return contactlist; //-- return contact list 29

30 long insert () Insert a row into the database Parameters table nullcolumnhack values the table to insert the row into opfonal; may be null this map contains the inifal column values for the row. The keys should be the column names and the values the column values Return the row ID of the newly inserted row, or -1 if an error occurred 30

31 insert Example public long addcontact(contact contact) { // SQL Statement: INSERT tblcontacts (name,phonenumber) VALUES ('a','1') SQLiteDatabase db = this.getwritabledatabase(); // Create ContentValues to pass insert method ContentValues values = new ContentValues(); values.put(col_name, contact.getname()); values.put(col_phone, contact.getphonenumber()); //-- insert new contact row long result = db.insert( TABLE_CONTACTS, // the table to insert the row into null, values); // this map contains the column values for the row. //-- close database connection db.close(); return result; } 31

32 Cursor query () Query the given table, returning a Cursor over the result set. Parameters table columns selecfon selecfonargs The table name to compile the query against A list of which columns to return. Passing null will return all columns A filter declaring which rows to return, forma\ed as an SQL WHERE clause (excluding the WHERE itself). Passing null will return all rows for the given table You may include?s in selecfon, which will be replaced by the values from selecfonargs, in order that they appear in the selecfon 32

33 Cursor query () Parameters groupby having orderby A filter declaring how to group rows, forma\ed as an SQL GROUP BY clause (excluding the GROUP BY itself). Passing null will cause the rows to not be grouped A filter declare which row groups to include in the cursor, if row grouping is being used, forma\ed as an SQL HAVING clause (excluding the HAVING itself). How to order the rows, forma\ed as an SQL ORDER BY clause (excluding the ORDER BY itself). Return A Cursor object, which is posifoned before the first entry 33

34 query Example public Contact getcontact(int id) { // SELECT id,name,phonenumber FROM tblcontacts SQLiteDatabase db = this.getreadabledatabase(); Contact contact = new Contact(); Cursor cursor = db.query( TABLE_CONTACTS, // The table name to compile the query against. new String[] { COL_KEY_ID, COL_NAME, COL_PHONE }, // A list of columns COL_KEY_ID + "=?, // SQL WHERE clause new String[] { String.valueOf(id) }, // selectionargs for WHERE clause null, // SQL GROUP BY null, // SQL HAVING clause null); // SQL ORDER BY clause } } if (cursor = null) { //-- Check cursor object for null cursor.movetofirst(); //-- Move the cursor to the first row contact.setid(cursor.getint(0)); //-- read id (0th col) from cursor contact.setname(cursor.getstring(1)); //-- read name (1th col) from cursor contact.setphonenumber(cursor.getstring(2)) //-- read phone (2th col) from cursor cursor.close(); //-- close cursor db.close(); //-- close database connection return contact; 34

35 int update () Update rows in the database. Parameters table values whereclause whereargs the table to update in a map from column names to new column values the opfonal WHERE clause to apply when updafng. Passing null will update all rows You may include?s in the where clause, which will be replaced by the values from whereargs Return the number of rows affected 35

36 update Example public int updatecontact(contact contact) { SQLiteDatabase db = this.getwritabledatabase(); // Create ContentValues to pass update method ContentValues values = new ContentValues(); values.put(col_name, contact.getname()); values.put(col_phone, contact.getphonenumber()); int result = db.update( TABLE_CONTACTS, // table values, // values COL_KEY_ID + " =?, // whereclause new String[] { String.valueOf(contact.getId()) }); // whereargs } //-- close resources db.close(); return result; 36

37 int delete () Delete rows in the database Parameters table whereclause whereargs the table to delete from the opfonal WHERE clause to apply when delefng. Passing null will delete all rows You may include?s in the where clause, which will be replaced by the values from whereargs Return the number of rows affected if a whereclause is passed in, 0 otherwise. To remove all rows and get a count pass "1" as the whereclause 37

38 delete Example public int deletecontact(contact contact) { // SQL Statement: DELETE FROM tblcontacts WHERE id =? SQLiteDatabase db = this.getwritabledatabase(); int result = db.delete( TABLE_CONTACTS, // table COL_KEY_ID + " =?", // whereclause new String[] { String.valueOf(contact.getId()) }); // whereargs } //-- close resources db.close(); return result; 38

39 Shared Preferances 39

40 SharedPreferences If you have a relatively small collection of key-values that you'd like to save, you should use the SharedPreferences API A SharedPreferences object points to a file containing key-value pairs and provides simple methods to read and write them Save and retrieve persistent key-value pairs of primitive data types boolean, float, int, long, string Each SharedPreferences file is managed by the framework and can be private or shared 40

41 Get SharedPreferences Object You can create a new shared preference file or access an existing one by calling one of two methods getsharedpreferences() - Use this if you need multiple shared preference files identified by name, which you specify with the first parameter getpreferences() - Use this from an Activity if you need to use only one shared preference file for the activity. Because this retrieves a default shared preference file that belongs to the activity, you don't need to supply a name 41

42 Get a SharedPreferences Object When naming your shared preference files, you should use a name that's uniquely identifiable to your app, such as com.mis49m.myapp.preference_file_key SharedPreferences sharedprefs = getsharedpreferences( getstring(r.string.preference_file_key), Context.MODE_PRIVATE); SharedPreferences sharedpref = getpreferences(context.mode_private); 42

43 Write to SharedPreferences Call edit() to get a SharedPreferences.Editor Add values with methods such as putboolean() and putstring() Commit the new values with commit() SharedPreferences sharedpref = getpreferences(context.mode_private); SharedPreferences.Editor editor = sharedpref.edit(); editor.putint("key", 1); editor.commit(); 43

44 Read from SharedPreferences Use SharedPreferences methods such as getboolean() getstring() SharedPreferences sharedpref = getpreferences(context.mode_private); long highscore = sharedpref.getint("key_high_score", 0); 44

45 Modes MODE_PRIVATE By setting this mode, the file can only be accessed using calling application MODE_WORLD_READABLE This mode allow other application to read the preferences MODE_WORLD_WRITEABLE This mode allow other application to write the preferences 45

SharedPreference. <map> <int name="access_count" value="3" /> </map>

SharedPreference. <map> <int name=access_count value=3 /> </map> 1 Android Data Storage Options Android provides several data storage options for you to save persistent application data depends on your specific needs: private/public, small/large datasets :- Internal