理解节点-mariasql示例代码

Question

我在节点-mariasql库上看到了以下代码-

var inspect = require('util').inspect;
var Client = require('mariasql');

var c = new Client();
c.connect({
  host: '127.0.0.1',
  user: 'foo',
  password: 'bar',
  db: 'mydb'
});

c.on('connect', function() {
   console.log('Client connected');
 })
 .on('error', function(err) {
   console.log('Client error: ' + err);
 })
 .on('close', function(hadError) {
   console.log('Client closed');
 });

var pq = c.prepare('SELECT * FROM users WHERE id = :id AND name = :name');

c.query(pq({ id: 1337, name: 'Frylock' }))
 .on('result', function(res) {
   res.on('row', function(row) {
     console.log('Result row: ' + inspect(row));
   })
   .on('error', function(err) {
     console.log('Result error: ' + inspect(err));
   })
   .on('end', function(info) {
     console.log('Result finished successfully');
   });
 })
 .on('end', function() {
   console.log('Done with all results');
 });

c.end();

这方面的输出已指定为-

/* output:
    Client connected
    Query #1 row: [ 'first query' ]
    Query #1 finished successfully
    Query #2 was aborted
    Query #3 row: [ 'third query' ]
    Query #3 finished successfully
    Done with all queries
    Client closed
 */

在我看来，c.connect似乎是一个异步调用。那么，代码的底部不应该放在c.on('connect')回调中吗？否则，当我执行c.query或c.prepare时，连接已经打开的保证是什么？

代码的底部部分。

var pq = c.prepare('SELECT * FROM users WHERE id = :id AND name = :name');

c.query(pq({
    id: 1337,
    name: 'Frylock'
}))
    .on('result', function (res) {
    res.on('row', function (row) {
        console.log('Result row: ' + inspect(row));
    })
        .on('error', function (err) {
        console.log('Result error: ' + inspect(err));
    })
        .on('end', function (info) {
        console.log('Result finished successfully');
    });
})
    .on('end', function () {
    console.log('Done with all results');
});

c.end();

Answer 1

mysql协议要求您在发送下一个命令之前等待前面的命令完成，因此大多数客户端自动具有某种类型的内部队列和移到队列中的下一个命令。例如，此代码不并行执行3次查询：

c.query('select sleep(1)');
c.query('select sleep(2)');
c.query('select 1', console.log);

相反，它将在3秒后输出"select 1“结果。因此，“连接已经打开的保证是什么”的答案是“客户端设计向您保证这一点”。