Transcript SQLite Library

SQLite
Supported by BlackBerry OS 5.0
Using SQLite
Overview
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SQLite Library
SQLite Database
Database Security Options
A Statement Life Cycle
Transactions
Remove Databases
Vacuum Command
Best Parctice
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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.
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SQLite Library (Cont.)
• The package that provides classes and
interfaces to work with SQLite is
“net.rim.device.api.database”.
• DB locations can be :
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SD Card: /SDCard/
Device memory: /store/home/user
System memory: /system/
Default location:
/SDCard/databases/<application_name>
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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.
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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);
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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.
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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/
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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))
}
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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);
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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”.
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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
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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)
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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
String dbLocation = "/SDCard/databases/myApplication/";
//Create a URI path file for the database
URI uri = URI.create(dbLocation + “myDB.db”);
//Specify security options to encrypt the database
DatabaseSecurityOptions dso = new DatabaseSecurityOptions(true);
// Invoke the create() or openOrCreate() method
Database db = DatabaseFactory.openOrCreate(uri, dso);
}
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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 ‘;’
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A statement lifecycle
• It represents a SQL statement.
• The lifecycle of a statement is:
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Create a statement
Prepare statement
Bind
Query Execution or
Update Execution
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Example- Create a Table
Public void createTable() throws Exception{
String dbLocation = "/SDCard/databases/myApplication/";
//Create a URI path file for the database
URI uri = URI.create(dbLocation + “myDB.db”);
Database db = DatabaseFactory.open(uri);
//Create a statement
Statement st = db.createStatement( “CREATE TABLE ‘Student’ ( ”
+ “ ‘Name’ TEXT,” + “ ‘ID’ INTEGER )”);
st.prepare();
st.execute();
}
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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.
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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);
bind(10, 50000);
// means salary <80000
// means salary >50000
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Example-Bind() method
Public void insertDataIntoTable() throws Exception{
String dbLocation = "/SDCard/databases/myApplication/";
URI uri = URI.create(dbLocation + “myDB.db”);
Database db = DatabaseFactory.open(uri);
Statement st = db.createStatement( “INSERT INTO Employee
VALUES(?, ?, ?)”);
st.prepare();
st.bind(1, employeeID);
st.bind(2, name);
st.bind(3, salary);
st.execute();
}
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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()
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Cursor Class
• Cursor provides read-only access to results
returned by getCursor() method
• It is an iterator. It provides one-way forwardonly navigation method.
• Methods:
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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
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Example- Cursor Class
Public void selectDataTable() throws Exception{
URI uri = URI.create("/SDCard/databases/myApplication/" + “myDB.db”);
Database db = DatabaseFactory.open(uri);
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();
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}
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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.
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Example – Execute()
method
Public void deleteTable() throws Exception{
String dbLocation = "/SDCard/databases/myApplication/";
URI uri = URI.create(dbLocation + “myDB.db”);
Database db = DatabaseFactory.open(uri);
Statement st = db.createStatement( “DELETE Employee”);
st.prepare();
st.execute();
}
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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.
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Example- reset() Method
Public void insertDataTable() throws Exception{
URI uri = URI.create("/SDCard/databases/myApplication/" + “myDB.db”);
Database db = DatabaseFactory.open(uri);
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();
}
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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.
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Example- Transaction
public void transactionStatement() {
URI uri = URI.create("/SDCard/databases/myApplication/" + “myDB.db”);
Database db = DatabaseFactory.open(uri);
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();
}
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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:
URI uri = URI.create("/SDCard/databases/myApplication/" + “myDB.db”);
//Remove the database from the device
DatabaseFactory.delete(uri);
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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.
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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.
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Best Practices
• In order to have a better performance when
developing a database application, consider
the following:
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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
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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.
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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
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References
1.
BlackBerry Java Application SQLite Version. 5.0 (Development Guide)
Available online at http://www.blackberry.com/developers
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