Question

我是节点js中的新手，现在我正在尝试使用节点js在mysql中设置select查询的返回值....我正在使用node-mysql包...

示例代码

var mysql =  require('mysql');
var connection =  mysql.createConnection({
    host : "localhost",
    user : "root",
    password: "root123",
    database: "testdb"
});

var retValue = undefined;

var query = connection.query('SELECT * FROM tblData;');
query
    .on('error', function(err) {
        // Handle error, an 'end' event will be emitted after this as well
    })
    .on('fields', function(fields) {
        // the field packets for the rows to follow
    })
    .on('result', function(row) {
        // Pausing the connnection is useful if your processing involves I/O
        connection.pause();
        processRow(row, function() {
            retValue = row;
        });
    })
    .on('end', function(row) {

    });

    connection.end();

    function processRow(rows)
    {
        retValue = rows;
    }

    console.log(retValue);

retValue始终未定义。我知道这是异步调用。有人告诉我如何设置这个变量的值。

由于迪帕克

Answer 1

由于数据库查询是异步操作，因此在您调用retValue时尚未设置变量console.log(retValue)。

var retValue;

var query = connection.query('SELECT * FROM tblData;');
query
    .on('error', function(err) {
        // Handle error, an 'end' event will be emitted after this as well
    })
    .on('fields', function(fields) {
        // the field packets for the rows to follow
    })
    .on('result', function(row) {
        // Pausing the connnection is useful if your processing involves I/O
        connection.pause();
        processRow(row);
        console.log(retValue); //retValue is now set
    })
    .on('end', function(row) {

    });

    connection.end();

    function processRow(rows)
    {
        retValue = rows;
    }

    console.log(retValue); // undefined, retValue has not been set yet

Answer 2

retvalue只在范围内可用，即你输入结果。所以你可以做类似的事情来记录你的结果：

var connection =  mysql.createConnection({
    host : "localhost",
    user : "root",
    password: "root123",
    database: "testdb"
});

var retValue = undefined;

var query = connection.query('SELECT * FROM tblData;', function(err, results, fields) {
    console.log(results);
    // Here continue logic you needed with results from table
});

Answer 3

将console.log移到function processRow(rows)内，使其看起来像

function processRow(rows)
{
    retValue = rows;
    console.log(retValue);
}

也改变了

processRow(row, function() {
    retValue = row;
});

要

processRow(row);

第二个参数未使用。

Answer 4

我无法从范围中得到结果...我想分配并返回这样的值

fucntion（）getResults { ... ... var retValue = undefined;

var query = connection.query（＆＃39; SELECT * FROM tblData;＆＃39;，function（err，results，fields）{ retValue =结果; }）;

返回retValue };

var ret = getResults（）; 的console.log（RET）;

无法使用mysql和节点js返回选择查询值

4 个答案: