Qt Quick 本地存储 QML 类型

This is a singleton type for reading and writing to SQLite databases.


  • object openDatabaseSync (string name, string version, string description, int estimated_size, jsobject callback(db))


To use the types in this module, import the module and call the relevant functions using the LocalStorage 类型:

import QtQuick
import QtQuick.LocalStorage
Item {
    Component.onCompleted: {
        var db = LocalStorage.openDatabaseSync(...)

These databases are user-specific and QML-specific, but accessible to all QML applications. They are stored in the 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:

import QtQuick 2.0
Rectangle {
    color: "white"
    width: 200
    height: 100
    Text {
        text: "?"
        anchors.horizontalCenter: parent.horizontalCenter
        function findGreetings() {
            var db = openDatabaseSync("QDeclarativeExampleDB", "1.0", "The Example QML SQL!", 1000000);
                function(tx) {
                    // Create the database if it doesn't already exist
                    tx.executeSql('CREATE TABLE IF NOT EXISTS Greeting(salutation TEXT, salutee TEXT)');
                    // Add (another) greeting row
                    tx.executeSql('INSERT INTO Greeting VALUES(?, ?)', [ 'hello', 'world' ]);
                    // Show all added greetings
                    var rs = tx.executeSql('SELECT * FROM Greeting');
                    var r = ""
                    for (var i = 0; i < rs.rows.length; i++) {
                        r += rs.rows.item(i).salutation + ", " + rs.rows.item(i).salutee + "\n"
                    text = r
        Component.onCompleted: findGreetings()

The API conforms to the Synchronous API of the HTML5 Web Database API, W3C Working Draft 29 October 2009 .

SQL 本地存储范例 演示使用离线存储 API 的基础知识。


import QtQuick.LocalStorage as Sql
db = Sql.openDatabaseSync(identifier, version, description, estimated_size, callback(db))

The above code returns the database identified by identifier . If the database does not already exist, it is created, and the function callback is called with the database as a parameter. identifier is the name of the physical file (with or without full path) containing the database. description and estimated_size are written to the INI file (described below), but are 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:

Identifier The name of the database passed to openDatabase()
版本 The version of the database passed to openDatabase()
描述 The description of the database passed to openDatabase()
EstimatedSize The estimated size (in bytes) of the database passed to openDatabase()
Driver Currently "QSQLITE"


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

This method allows you to perform a Scheme Upgrade . If it succeeds it returns a new database object of version to . Otherwise it returns undefined .

If the current version of db 不是 from , then an exception is thrown.

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

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

See example below.

    var db = LocalStorage.openDatabaseSync("ActivityTrackDB", "", "Database tracking sports
activities", 1000000); if (db.version == "0.1") { db.changeVersion("0.1", "0.2", function(tx) {
            tx.executeSql("INSERT INTO trip_log VALUES(?, ?, ?)",
                        [ "01/10/2016","Sylling - Vikersund", "53" ]);


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

If the callback throws exceptions, the transaction is rolled back. Below you will find an example of a database transaction which catches exceptions.

    var db = LocalStorage.openDatabaseSync("Activity_Tracker_DB", "", "Track exercise", 1000000)
    try {
        db.transaction(function (tx) {
            tx.executeSql('CREATE TABLE IF NOT EXISTS trip_log (date text,trip_desc text,distance numeric)')
    } catch (err) {
        console.log("Error creating table in database: " + err)

In the example you can see an insert statement where values are assigned to the fields, and the record is written into the table. That is an insert statement with a syntax that is usual for a relational database. It is however also possible to work with JSON objects and store them in a table.

Let's suppose a simple example where we store trips in JSON format using date as the unique key. An example of a table that could be used for that purpose:

create table trip_log(date text, data text)

The assignment of values to a JSON object:

var obj = {description = "Vikersund - Noresund", distance = "60"}

In that case, the data could be saved in the following way:

db.transaction(function(tx) {
    result = tx.executeSQL("insert into trip_log values (?,?)",
                           ["01/11/2016", JSON.stringify(obj)])


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

results = tx.executeSql(statement, values)

This method executes an SQL 语句 , binding the list of values to SQL positional parameters ("?").

It returns a results object, with the following properties:

Type 特性 Applicability
int rows.length 结果中的行数 SELECT
var rows.item(i) Function that returns row i of the result SELECT
int rowsAffected The number of rows affected by a modification UPDATE, DELETE
string insertId 插入行的 ID INSERT

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


function dbReadAll()
    var db = dbGetHandle()
    db.transaction(function (tx) {
        var results = tx.executeSql(
                    'SELECT rowid,date,trip_desc,distance FROM trip_log order by rowid desc')
        for (var i = 0; i < results.rows.length; i++) {
                                 id: results.rows.item(i).rowid,
                                 checked: " ",
                                 date: results.rows.item(i).date,
                                 trip_desc: results.rows.item(i).trip_desc,
                                 distance: results.rows.item(i).distance


object openDatabaseSync(string name, string version, string description, int estimated_size,
jsobject callback(db))

Opens or creates a local storage sql database by the given parameters.

  • name is the database name
  • version is the database version
  • description is the database display name
  • estimated_size is the database's estimated size, in bytes
  • callback is an optional parameter, which is invoked if the database has not yet been created.