Is local database a new feature of HTML5?-Front-end Q&A-php.cn

Is local database a new feature of HTML5?

青灯夜游

Release： 2022-01-23 16:41:18

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Local database is a new feature of html5. Html5 provides a browser-side database support, allowing developers to create a local database on the browser side directly through the JS API, and supports standard SQL CRUD operations, making offline web applications more convenient to store structured data. .

Is local database a new feature of HTML5?

The operating environment of this tutorial: Windows 7 system, HTML5 version, Dell G3 computer.

Although Html5 has provided powerful localStorage and sessionStorage, both of them can only provide data for storing simple data structures, and are powerless for complex web application data. What’s incredible is that Html5 provides a database support on the browser side, allowing us to create a local database on the browser side directly through the JS API, and supports standard SQL CRUD operations, making offline web applications more convenient to store structures. ized data. Next, we will introduce the relevant APIs and usage of local data.

The most basic steps to operate a local database are:

The first step: openDatabase method: Create an object to access the database.
Step 2: Use the database access object created in the first step to execute the transaction method. Through this method, you can set an event response method to start the transaction successfully. In the event response method, you can execute SQL.
Step 3: Execute the query through the executeSql method. Of course, the query can be: CRUD.

Next, we will introduce the parameters and usage of the relevant methods.

(1) openDatabase method:

//Demo：获取或者创建一个数据库，如果数据库不存在那么创建之
var dataBase = openDatabase("student", "1.0", "学生表", 1024 * 1024, function () { });

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The openDatabase method opens an existing database. If the database does not exist, it can also create a database. The meanings of several parameters are:

1, database name.
2. The version number of the database. Currently, 1.0 is enough. Of course, you don’t need to fill it in;
3. The description of the database.
4, set the size of the allocated database (unit is kb).
5, callback function (can be omitted).
Create the database when calling for the first time, and then establish the connection.

(2) The db.transaction method can set a callback function. This function can accept a parameter that is the object of the transaction we started. Then the Sql script can be executed through this object, which can be combined with the following steps.

(3) Execute the query through the executeSql method.

ts.executeSql(sqlQuery,[value1,value2..],dataHandler,errorHandler)

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Parameter description:

qlQuery: SQL statement that needs to be executed specifically, which can be create, select, update, delete;
value1,value2..] : An array of all parameters used in the sql statement. In the executeSql method, first replace the parameters to be used in the s> statement with "?", and then form an array of these parameters and place them in the second parameter.
ataHandler: The callback function called when the execution is successful, through which the query result set can be obtained;
4, errorHandler: The callback function called when the execution fails;

The following It is a comprehensive example, you can take a look:

<head>
 <script src="Scripts/jquery-1.5.1.js" type="text/javascript"></script>
    <script type="text/javascript">
        function initDatabase() {
            var db = getCurrentDb();//初始化数据库
            if(!db) {alert("您的浏览器不支持HTML5本地数据库");return;}
            db.transaction(function (trans) {//启动一个事务，并设置回调函数
                //执行创建表的Sql脚本
                trans.executeSql("create table if not exists Demo(uName text null,title text null,words text null)", [], function (trans, result) {
                }, function (trans, message) {//消息的回调函数alert(message);});
            }, function (trans, result) {
            }, function (trans, message) {
            });
        }
        $(function () {//页面加载完成后绑定页面按钮的点击事件
            initDatabase();
            $("#btnSave").click(function () {
                var txtName = $("#txtName").val();
                var txtTitle = $("#txtTitle").val();
                var txtWords = $("#txtWords").val();
                var db = getCurrentDb();
                //执行sql脚本，插入数据
                db.transaction(function (trans) {
                    trans.executeSql("insert into Demo(uName,title,words) values(?,?,?) ", [txtName, txtTitle, txtWords], function (ts, data) {
                    }, function (ts, message) {
                        alert(message);
                    });
                });
                showAllTheData();
            });
        });
        function getCurrentDb() {
            //打开数据库，或者直接连接数据库参数：数据库名称，版本，概述，大小
            //如果数据库不存在那么创建之
            var db = openDatabase("myDb", "1.0", "it&#39;s to save demo data!", 1024 * 1024); ;
            return db;
        }
        //显示所有数据库中的数据到页面上去
        function showAllTheData() {
            $("#tblData").empty();
            var db = getCurrentDb();
            db.transaction(function (trans) {
                trans.executeSql("select * from Demo ", [], function (ts, data) {
                    if (data) {
                        for (var i = 0; i < data.rows.length; i++) {
                            appendDataToTable(data.rows.item(i));//获取某行数据的json对象
                        }
                    }
                }, function (ts, message) {alert(message);var tst = message;});
            });
        }
        function appendDataToTable(data) {//将数据展示到表格里面
            //uName,title,words
            var txtName = data.uName;
            var txtTitle = data.title;
            var words = data.words;
            var strHtml = "";
            strHtml += "<tr>";
            strHtml += "<td>"+txtName+"</td>";
            strHtml += "<td>" + txtTitle + "</td>";
            strHtml += "<td>" + words + "</td>";
            strHtml += "</tr>";
            $("#tblData").append(strHtml);
        }
    </script>
</head>
    <body>
        <table>
            <tr>
                <td>用户名：</td>
                <td><input type="text" name="txtName" id="txtName" required/></td>
            </tr>
               <tr>
                <td>标题：</td>
                <td><input type="text" name="txtTitle" id="txtTitle" required/></td>
            </tr>
            <tr>
                <td>留言：</td>
                <td><input type="text" name="txtWords" id="txtWords" required/></td>
            </tr>
        </table>
        <input type="button" value="保存" id="btnSave"/>
        <hr/>
        <input type="button" value="展示所哟数据" onclick="showAllTheData();"/>
        <table id="tblData">
        </table>
    </body>
</html>

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The execution effect is as shown in the figure:

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