使用node-mysql创建同步查询

我正在尝试确保一个mysql查询导致另一个mysql查询,并且在完成所有子查询之前不会完成.例如,我从一个select和stream行开始,然后从该行结果执行后续查询.这对回调来说是可行的,但是我最终耗尽内存,所以我想放慢进程并运行批处理,但由于调度的异步性质,我无法保持同步并结束处理完所有行后的连接.

这是一个例子：

var query = conn.query('select id from table1 limit 10');

query.on('result', function(row){
    console.log('query1', row);
    var query2 = conn.query('select id from books where id  = ? ', [row.id]);
    query2.on('result', function(row2){
        console.log('query2', row2);
        var query3 = conn.query('insert into test (id) values (?)', [row2.id]);
        query3.on('result', function(row3){
            console.log(row3);
        });
    });
});

query.on('end', function(){
    conn.end();
});

上述操作失败,因为在初始查询结束后仍有一些行要在query3中处理.
有什么想法吗？实际代码更加复杂,因为我必须处理后续查询中的xml,并在循环批处理时触发更多插入.

谢谢！

解决方法:

我建议用async模块解决这个问题：

var async = require("async");
// connection instance
var conn;

// here goes task serving logic
// if any async function should be finished before drain callback, push them into q
var solvers = {
    query: function(q, task, row){
        console.log('query1', row);
        q.push({
            solver: "query2",
            req: "select id from books where id = ?",
            reqArgs: [row.id]
        });
    },
    query2: function(q, task, row){
        console.log('query2', row);
        q.push({
            solver: "query3",
            req: "insert into test (id) values (?)",
            reqArgs: [row.id]
        });
    },
    query3: function(q, task, row){
        console.log(row);
    }
}

// here is a queue of tasks
var q = async.queue(function(task, cb){
    var query = conn.query(task.req, task.reqArgs);
    query.on("end", cb);
    query.on("result",function(row){
        solvers[task.solver](q, task, row);
    });
}, 2); // limit of parallel queries

// when every request has reached "end"
q.drain = function(){
    conn.end();
    // continue from here
};

// initial task
q.push({
    solver: "query",
    req: "select id from table1 limit 10",
    reqArgs: []
});

但是,我仍然不确定通过ID提出ID请求是一个很好的解决方案.
也许,我只是不知道一个完整的问题.

标签：mysql,node-js,node-mysql
来源： https://codeday.me/bug/20190528/1173714.html