Javascript SQL插入循环 [英] Javascript SQL Insert Loop

问题描述

我正在尝试向函数传递一个数组，该数组应该通过循环运行，并为每个递增的SQL语句调用db.transaction.

I'm attempting to pass a function an array that should run through a loop and call a db.transaction for each incremented SQL statement.

function updateColorData (colorArray) {
    for (var i=0; i<colorArray.length; i++) {
        var sql = 'INSERT INTO SPColorData (color) VALUES (\''+colorArray[i]+'\')';
        if (i < colorArray.length-1) {
            db.transaction(function (tx) {tx.executeSql(sql, [], gameOptionSuccess, errorCB)}, errorCB);
        } else {
            db.transaction(function (tx) {tx.executeSql(sql, [], colorDataQuery, errorCB)}, errorCB);
        }
    }
}

作为测试，我将调用updateColorData函数传入这样的数组中

As a test I'm calling the updateColorData function passing in an array like this

['one', 'two', 'three', 'four']

但是当我让数据库读回它收到的信息时，我会得到

but when I have the database read back the information it received I'm getting

['four', 'four', 'four', 'four']

我意识到在这样的循环中调用4个数据库事务并不是最有效的方法，但是我不确定为什么它不起作用或尝试其他方法.

I realize that calling 4 database transactions in a loop like this is not the most efficient method but I'm not sure why this isn't working or what other method to try.

谢谢！

推荐答案

在调用数据库函数之前，您需要为 i 创建一个新作用域；试试这个:

You need to create a new scope for i before you call the database function; try this:

function updateColorData (colorArray) {
    for (var i=0; i<colorArray.length; i++) {
        (function(i){
            var sql = 'INSERT INTO SPColorData (color) VALUES   (\''+colorArray[i]+'\')';
            if (i < colorArray.length-1) {
                db.transaction(function (tx) {tx.executeSql(sql, [], gameOptionSuccess, errorCB)}, errorCB);
            } else {
            db.transaction(function (tx) {tx.executeSql(sql, [], colorDataQuery, errorCB)}, errorCB);
            }
        })(i);
    }
}

使用匿名函数为 i 的每个值创建一个单独的函数作用域.您需要执行此操作，因为原始示例中的 for 循环会不断更新 i ，而无需等待数据库函数返回.因此，您需要为数据库函数创建安全"上下文，以在不更改 i 值的情况下运行数据库函数，而这正是匿名函数所提供的.

That creates an individual function scope for each value of i, using an anonymous function. You need to do this because the for loop in your original example keeps updating i without waiting for your database function to return. So you need to create "safe" contexts for your database functions to run without the for loop changing the value of i, and that's exactly what the anonymous functions provide.

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