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/*!
\page qml-localstorage.html
\title QML Local Storage
\brief SQL storage for QML

The local storage API provides a JavaScript interface to an SQL relational
database. The QtQuick.LocalStorage module contains the API and it may be given
a namespace.

Import QtQuick.LocalStorage module from QML:
\code
//sql.qml

import QtQuick.LocalStorage 2.0 as Sql
\endcode


Import QtQuick.LocalStorage module from JavaScript:
\code
//sql.js
.import QtQuick.LocalStorage 2.0 as Sql
\endcode

Note, importing a module from JavaScript is different from importing from QML.
The \l{JavaScript Code} article contains detailed information on importing in JavaScript code.


\section2 Database API

The \c openDatabaseSync() and related functions
provide the ability to access local storage in an SQL database.

These databases are user-specific and QML-specific, but accessible to all QML applications.
They are stored in the \c Databases subdirectory
of QQmlEngine::offlineStoragePath(), currently as SQLite databases.

Database connections are automatically closed during Javascript garbage collection.

The API can be used from JavaScript functions in your QML:

\snippet declarative/sqllocalstorage/hello.qml 0

The API conforms to the Synchronous API of the HTML5 Web Database API,
\link http://www.w3.org/TR/2009/WD-webdatabase-20091029/ W3C Working Draft 29 October 2009\endlink.

The \l{declarative/sqllocalstorage}{SQL Local Storage example} demonstrates the basics of
using the Local Storage API.

\section3 db = openDatabaseSync(identifier, version, description, estimated_size, callback(db))

Returns the database identified by \i identifier. If the database does not already exist, it
is created, and the function \i callback is called with the database as a parameter. \i description
and \i estimated_size are written to the INI file (described below), but are otherwise currently
unused.

May throw exception with code property SQLException.DATABASE_ERR, or SQLException.VERSION_ERR.

When a database is first created, an INI file is also created specifying its characteristics:

\table
\header \o \bold {Key} \o \bold {Value}
\row \o Name \o The name of the database passed to \c openDatabase()
\row \o Version \o The version of the database passed to \c openDatabase()
\row \o Description \o The description of the database passed to \c openDatabase()
\row \o EstimatedSize \o The estimated size (in bytes) of the database passed to \c openDatabase()
\row \o Driver \o Currently "QSQLITE"
\endtable

This data can be used by application tools.

\section3 db.changeVersion(from, to, callback(tx))

This method allows you to perform a \i{Scheme Upgrade}.

If the current version of \i db is not \i from, then an exception is thrown.

Otherwise, a database transaction is created and passed to \i callback. In this function,
you can call \i executeSql on \i tx to upgrade the database.

May throw exception with code property SQLException.DATABASE_ERR or SQLException.UNKNOWN_ERR.

\section3 db.transaction(callback(tx))

This method creates a read/write transaction and passed to \i callback. In this function,
you can call \i executeSql on \i tx to read and modify the database.

If the callback throws exceptions, the transaction is rolled back.

\section3 db.readTransaction(callback(tx))

This method creates a read-only transaction and passed to \i callback. In this function,
you can call \i executeSql on \i tx to read the database (with SELECT statements).

\section3 results = tx.executeSql(statement, values)

This method executes a SQL \i statement, binding the list of \i values to SQL positional parameters ("?").

It returns a results object, with the following properties:

\table
\header \o \bold {Type} \o \bold {Property} \o \bold {Value} \o \bold {Applicability}
\row \o int \o rows.length \o The number of rows in the result \o SELECT
\row \o var \o rows.item(i) \o Function that returns row \i i of the result \o SELECT
\row \o int \o rowsAffected \o The number of rows affected by a modification \o UPDATE, DELETE
\row \o string \o insertId \o The id of the row inserted \o INSERT
\endtable

May throw exception with code property SQLException.DATABASE_ERR, SQLException.SYNTAX_ERR, or SQLException.UNKNOWN_ERR.



*/