Question

亲爱的Stackoverflow用户，

我们创建的数据库如下：

function populateDB(tx) {
    tx.executeSql('DROP TABLE IF EXISTS Gerechten');
    tx.executeSql('CREATE TABLE IF NOT EXISTS Gerechten (id INTEGER PRIMARY KEY AUTOINCREMENT, Cat TEXT NOT NULL, Name TEXT NOT NULL, Desc TEXT NOT NULL)');
    tx.executeSql('INSERT INTO Gerechten(Cat,Name,Desc) VALUES ("Voorgerecht", "Tomatensoep", "Heerlijke romige tomatensoep")');
    tx.executeSql('INSERT INTO Gerechten(Cat,Name,Desc) VALUES ("Hoofdgerecht", "Pizza", "Kaas en tomaat")');
    tx.executeSql('INSERT INTO Gerechten(Cat,Name,Desc) VALUES ("Voorgerecht", "Groentensoep", "Goed gevulde groentensoep")');
    tx.executeSql('INSERT INTO Gerechten(Cat,Name,Desc) VALUES ("Voorgerecht", "Kippensoep", "Kippensoep met stukjes kip")');
    tx.executeSql('INSERT INTO Gerechten(Cat,Name,Desc) VALUES ("Hoofdgerecht", "Biefstuk", "Biefstuk, wordt geserveerd met patat of rijst")');
}

我的Javascript循环有问题，代码如下：

function queryDB(tx){
    tx.executeSql('SELECT DISTINCT "Cat" FROM Gerechten',[],function (tx, results) {
        var len = results.rows.length, i;
        msg = "<p>Found rows: " + len + "</p>";
        document.write(msg + '<br/>');
        for (i = 0; i < len; i++){
            document.write(results.rows.item(i).Cat + '<br/>');
            tx.executeSql('SELECT * FROM Gerechten WHERE "Cat" ="'+results.rows.item(i).Cat+'"',[],function (tx, results2) {
                var len2 = results2.rows.length, y;
                msg = "<p>Found rows: " + len2 + "</p>";
                document.write(msg + '<br/>');
                for (y = 0; y < len2; y++){
                    document.write(results2.rows.item(y).Name + '<br/>');
                }
            }, null);
        }
    }, null);
}

代码的问题是首先输出类别，然后显示名称（按照正确的顺序）：

Voorgerecht
Hoofdgerecht
  Tomatensoep
  Groentensoep
  Kippensoep
  Pizza
  Biefstuk

正确的顺序应该是：

Voorgerecht
  Tomatensoep
  Groentensoep
  Kippensoep
Hoofdgerecht
  Pizza
  Biefstuk

有谁知道如何解决这个问题？

亲切的问候，

丹尼斯

Answer 1

你的问题是executeSql异步执行你的函数（它的最后一个参数），所以你的外循环很可能在内循环的查询完成执行之前打印所有类别。

您应该只使用一个查询，以便您可以按正确的顺序处理所有结果。尝试这样的事情：

SELECT * FROM Gerechten ORDER BY Cat

并在Cat列中的值发生变化时打印该类别（请参阅Jose的回答）。

Answer 2

老实说，你不需要多次查询数据库，假设：

SELECT * FROM Gerechten

，您的搜索结果包含以下内容you could do as below and still produce the same results。显然你需要实现它以匹配你的web sql数据库api，但逻辑应该保持不变。

var results = [
    {
        "Cat" : "Voorgerecht",
        "Name" : "Tomatensoep",
        "Desc" : "Heerlijke romige tomatensoep"
    },{
        "Cat" : "Hoofdgerecht",
        "Name" : "Pizza",
        "Desc" : "Kaas en tomaat"
    },{
        "Cat" : "Voorgerecht",
        "Name" : "Groentensoep",
        "Desc" : "Goed gevulde groentensoep"
    },{
        "Cat" : "Voorgerecht",
        "Name" : "Kippensoep",
        "Desc" : "Kippensoep met stukjes kip"
    },{
        "Cat" : "Hoofdgerecht",
        "Name" : "Biefstuk",
        "Desc" : "wordt geserveerd met patat of rijst"
    }
];

//sorts by the Category
results.sort(compare);
var initial = "";

for(var y = 0; results.length; y++) {
    if(initial != results[y].Cat){
        initial = results[y].Cat;
         document.write(initial + "<br/>");
    }

    document.write("&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;" + results[y].Name + "<br/>");
}


function compare(a,b) {
    if (a.Cat < b.Cat)
        return 1;
    if (a.Cat > b.Cat)
        return -1;    
    else
      return 0;
}

输出

Voorgerecht
     Tomatensoep
     Groentensoep
     Kippensoep
Hoofdgerecht
     Pizza
     Biefstuk

使用Javascript和SQLite时订单错误

2 个答案: