SQLite Supported by BlackBerry OS 5.0 Using SQLite

1

SQLiteSupported by BlackBerry OS 5.0

Using SQLite

2http://cmer.cis.uoguelph.ca

Overview

• SQLite Library• SQLite Database• Database Security Options• A Statement Life Cycle• Transactions• Remove Databases• Vacuum Command• Best Parctice


SQLite Library

• It is a relational database library.• Has a small footprint. Hence, it is good for

small devices.• BlackBerry devices that run BlackBerry Device

Software version 5.0 or later supports SQLite library.

• SQLite library has been introduced in BlackBerry Java Development Environment Version 5 and later.


SQLite Library (Cont.)

• The package that provides classes and interfaces to work with SQLite is “net.rim.device.api.database”.

• DB locations can be :– SD Card: /SDCard/– Device memory: /store/home/user– System memory: /system/– Default location:

/SDCard/databases/<application_name>


SQLite Database

• SQLite database is stored in a single file on a SD Card.

• The default location for a SQLite database is /SDCard/databases/<application_name>

• You can store the database file in the device memory by specifying the file system path

• It can be encrypted or plain text.


How to Create a Plain Database

• Import net.rim.device.api.database that include classes to work with SQLite.

• Create a URI representing the database file– dbURI =

URI.create(“file:///SDCard/Databases/myApplication/”+ “MyDatabase.db”);

• Invoke the Create() method of the DatabaseFactory class to create a new database– Database d = DatabaseFactory.create(dbURI);


How to Create a Plain Database

• -or –• Invoke openorCreate() to create a new

database or open an existing one.– Database db = DatabaseFactory.openOrCreate(uri);

• You can also create an encrypted database by specifying security options in Create() or openOrCreate() method.


How to Create a Plain Database (Cont.)

• DatabaseFactory:– Creates new or open existing instances of a device

database– Databases can be created temporary (in-memory)

or persistent depending on the URI path – URI path can be one of the DB locations presented

in the previous slides.• Example: create a database in device memory:

– URI path: /store/home/user• Create a database in system memory:

– URI path: /system/


Example- Open or Create a Database

public void createPlainDatabaseFile() throws Exception {

// The database is created in SD card

String dbLocation = "/SDCard/databases/myApplication/";

//if you want to create the database in flash memory use the following URI

// dbLocation = "/store/home/user/";

//Create a URI path file for the database

URI uri = URI.create(dbLocation + “myDB.db”);

// Invoke the create() or openOrCreate() method

Database db = DatabaseFactory.openOrCreate(uri, new DatabaseSecurityOptions(false))

}


Encrypted Databases

• A database can be encrypted by specifying the security options in Creat() or openOrCreate() method:– DatabaseFactory.create(URI fileURI,

DatabaseSecurityOptions securityOptions);– DatabaseFactory.openOrCreate(URI fileURI,

DatabaseSecurityOptions securityOptions);

•


Encrypted Databases (Cont.)

• When a database is encrypted, it is linked to the device in which it is created. So, it does not support portability between databases.

• In order to transfer the encrypted database to the other device, you have to decrypt it first.

• An encrypted database should be closed as soon as possible, otherwise, it is susceptible to “cold boot attack”.


DatabaseSecurity Options

• DatabaseSecurityOptions defines the security options for a database.

• There are three choices available:– Not encrypted, accessible from any application – Encrypted, accessible from any application – Encrypted and protected, accessible only from

applications that are signed with code signed key


DatabaseSecurity Options (Cont.)

• If two applications are signed with the same key, then both applications have access to the database.

• Methods:– Public DatabaseSecurityOptions(boolean encrypted)

• If encrypted is true, it means that the database is encrypted and not portable

– Public DatabaseSecurityOptions(CodeSigningKey key)– public DatabaseSecurityOptions(int signerId)


Example- Encrypted Database

• It opens or creates an encrypted database file. It is not portable between devices.

public void createEncryptedDatabaseFile() throws Exception {

// The database is created in SD card




//Specify security options to encrypt the database

DatabaseSecurityOptions dso = new DatabaseSecurityOptions(true);

// Invoke the create() or openOrCreate() method

Database db = DatabaseFactory.openOrCreate(uri, dso);

}


Database Class

• Database class allows to create, delete and execute SQL statements

• In order to create a SQL statement, invoke createStatement() method of Database class.– Statement createStatement(String sqlStatement)

• Creates a Statement in this database.

• The argument can contain multiple SQL Statements delimited by ‘;’


A statement lifecycle

• It represents a SQL statement.• The lifecycle of a statement is:

– Create a statement– Prepare statement– Bind – Query Execution or – Update Execution


Example- Create a Table

Public void createTable() throws Exception{String dbLocation = "/SDCard/databases/myApplication/";



Database db = DatabaseFactory.open(uri);

//Create a statement

Statement st = db.createStatement( “CREATE TABLE ‘Student’ ( ” + “ ‘Name’ TEXT,” + “ ‘ID’ INTEGER )”);

st.prepare();

st.execute();

}


Bind() Method

• If the SQL statement has parameters, you have to invoke bind() method to bind the parameter to a value.

• Statement.bind() has two arguments: the first argument is the parameter number and the second parameter is the value to bound to it.

• The occurance of ? in a statement means parameters are numbered sequentially.


Bind() Method (Cont.)

• The occurance ?NN in a SQL statement means that each parameter is numbered as integer NN.

• Example:Statement s = “SELECT * FROM Employee WHERE

salary < ?2 AND salary > ?10”;

Means that:bind(2, 80000); // means salary <80000

bind(10, 50000); // means salary >50000


Example-Bind() method

Public void insertDataIntoTable() throws Exception{




Statement st = db.createStatement( “INSERT INTO Employee VALUES(?, ?, ?)”);

st.prepare();

st.bind(1, employeeID);

st.bind(2, name);

st.bind(3, salary);

st.execute();

}


Query Execution

• Query execution is done using getCursor() method.

• getCursor() executes only SELECT queries and returns cursor with selected rows .

• The returned cursor is positioned before the first row. Hence, to get the current row, invoke Cursor.first() or Cursor.next() method.

• The method’s signature: Cursor getCursor()


Cursor Class

• Cursor provides read-only access to results returned by getCursor() method

• It is an iterator. It provides one-way forward-only navigation method.

• Methods:– getRow(): returns current row with values– next(): move the cursor to the next row– prev(): move cursor to the previous row– isEmpty(): determines whether cursor has rows– close(): closes cursor object


Example- Cursor ClassPublic void selectDataTable() throws Exception{

URI uri = URI.create("/SDCard/databases/myApplication/" + “myDB.db”);


Statement st = db.createStatement( “SELECT * FROM Employee”);

st.prepare();

Cursor cursor = st.getCursor();

while(cursor.next()) {

row = cursor.getRow();

id = row.getInteger(0);

name = row.getString(1);

salary = tow.getInteger(2);

}

st.close();

cursor.close();

}


Update Execution

• To update execution, invoke execute() method• Statement.execute() executes an update

statement. It does not return a result set.• If the query statement is NOT SELECT type,

invoke this method. You can use for any other SQL statement like INSERT, DELETE, CREATE, UPDATE and so on.


Example – Execute() method

Public void deleteTable() throws Exception{String dbLocation = "/SDCard/databases/myApplication/";



Statement st = db.createStatement( “DELETE Employee”);

st.prepare();

st.execute();

}


Reset() method

• Statement. reset() method resets the statement to its state after prepare() method.

• It also clears all bindings.• After invoking reset() method, execute() must

be called to het a new cursor.• So, if several SQL statements are run, invoke

reset() method after each execute() mthod to clear bindings and clear the statement state.


Example- reset() Method

Public void insertDataTable() throws Exception{



Statement st = db.createStatement(“INSERT INTO Employee VALUES(?, ?)”);

st.prepare();

while(count <10) {

st.bind(1,count);

st.bind(2, employee[count]);

st.execute();

st.reset();

count++;

}

st.close();

}


Transactions

• In order to execute multiple statements in one transaction, two methods should be called:– beginTransaction():

• Starts a new transaction. So, all of the following statement executions can be committed or rolled back.

– commitTransaction()• Commits current transaction starting with the

beginTransaction(). Before committing the transaction, all the cursors started within this transaction should be closed otherwise, the transaction is failed.

• Nested transactions are not supported.


Example- Transaction

public void transactionStatement() {



db.beginTransaction();

Statement st = db.createStatement(“INSERT INTO Employee VALUES(1, ‘Bob’)”);

st.prepare();

st.execute();

st.reset();

Statement st = db.createStatement(“INSERT INTO Employee VALUES(2, ‘John’)”);

st.prepare();

st.execute();

db.commitTransaction();

}


Delete a Database

• Invoke DatabaseFactory.delete() to remove an exisiting database from the device.

• The method’s signature:public static void delete( URI fileURI)

• Example:


//Remove the database from the device

DatabaseFactory.delete(uri);


Vacuum Command

• Database is stored as a file. Some operations such as dropping a table, inserting or deleting data, cause the file to be fragmented.

• Vacuum command is used to defragment and reduce the size of the database file.

• To defragment the file, Vacuum command copies all pieces of the file into the memory and creates a new database file.


Vacuum Command (Cont.)

• Because Vacuum copies all information related to the database into the memory, it needs enough memory.

• If enough memory is not available, the Vacuum command is failed.


Best Practices

• In order to have a better performance when developing a database application, consider the following:– Use local variables– Use primitive types instead of classes– Use static variables instead of Strings– Use efficient algorithms– Write efficient loops– Avoid Java.util.Enumeration


Best Practices (Cont.)

– Make classes final • Using final keyword means that it would never be

extended.

– Use int instead of long• long is a 64-bit integer

– Avoid unnecessary field initialization• Explicitly initialize local variables

– Use temporary tables as much as possible• It takes less recourses.


Best Practices (Cont.)

– Store data as little as possible• The search is faster.

– Avoid subqueries• Because the result is stored in a temporary file

– Use static inner class• Reduce the number of references


References

1. BlackBerry Java Application SQLite Version. 5.0 (Development Guide)

Available online at http://www.blackberry.com/developers

Documents

SQLite Supported by BlackBerry OS 5.0 Using SQLite