筛选数据后执行操作

Question

我正在将数据填充到数组中。我向Postgress中的数据库发出了很多请求，并且我想将完成的数组响应给客户端。问题是，当通知数组完成时我无法到达，我怎么能知道过滤器何时完成了对db的所有选择调用？

result.filter(function(item){ 
       //console.log(item.followed_by) 
       var query2 = 'SELECT user_id,action,date,element_refered FROM "notifications" WHERE user_id=' + "'"+ item.followed_by +"'" 

       dbp.sendDBRequest(query2,'blabla',function(results){ 
       notifications.push(results) 
        console.log(notifications) //here has data 
       }) 
      }) 
console.log(notifications) //here it doesnt have data 

我有诺言尝试BT认为我没有错：

  var p1 = new Promise(
    function(resolve, reject) { 
    result.filter(function(item){ 
      var query2 = 'SELECT user_id,action,date,element_refered FROM "notifications" WHERE user_id=' + "'"+ item.followed_by +"'" 
      dbp.sendDBRequest(query2,'blabla',function(results){ 
      notifications.push(results) 
      }) 
     }) 

      resolve(notifications); 
    } 
); 

    p1.then(
    function(val) { 
     console.log(notifications) 
    }) 
    .catch(
    function(reason) { 
     console.log('Manejar promesa rechazada ('+reason+') aquí.'); 
    }); 

编辑代码：

这与承诺的代码，但我得到了那么是不是一个过滤器（... ）。然后不是函数

var notifications = [] 
      var query = 'SELECT followed_by FROM "relations" WHERE follower=' +"'"+32+"'" 
      dbp.sendDBRequest(query,'blabla', function(result) { 
      result.filter(function(item) { 
      return new Promise(function(resolve, reject) { 
       var query2 = 'SELECT user_id,action,date,element_refered FROM "notifications" WHERE user_id=' + "'" + item.followed_by + "'" 
       dbp.sendDBRequest(query2, 'blabla', function(results) { 
       notifications.push(results); 
       resolve(notifications); 
      }) 
      }) 
      .then(function(val) { 
       console.log(notifications) 
      }) 
      .catch(function(reason) { 
       console.log('Manejar promesa rechazada (' + reason + ') aquí.'); 
      }); 
      }) 
      .then(function(response){ 
      var secondResponse = response + '2'; 
      return response; 
      }) 
      .then(function(secondResponse) { 
    //facultad 
}) 
      .catch(function(err){ 
       console.log(err)  
      }) 

     }) 

Answer 1

是的，你需要在你的主函数中承诺，它会返回promise对象。

result.filter(function(item) { 
    new Promise(function(resolve, reject) { 
     var query2 = 'SELECT user_id,action,date,element_refered FROM "notifications" WHERE user_id=' + "'" + item.followed_by + "'" 
     dbp.sendDBRequest(query2, 'blabla', function(results) { 
     notifications.push(results); 
     resolve(notifications); 
     }) 
    }) 
    .then(function(val) { 
     console.log(notifications) 
    }) 
    .catch(function(reason) { 
     console.log('Manejar promesa rechazada (' + reason + ') aquí.'); 
    }); 
}) 

然后，你可以处理然后抓块。 此外，如果你想继续，你可以返回无极对象，并增加额外再搭上......在最后

result.filter(function(item) { 
    return new Promise(function(resolve, reject) { 
     var query2 = 'SELECT user_id,action,date,element_refered FROM "notifications" WHERE user_id=' + "'" + item.followed_by + "'" 
     dbp.sendDBRequest(query2, 'blabla', function(results) { 
     notifications.push(results); 
     resolve(notifications); 
     }) 
    }) 
    .then(function(val) { 
     console.log(notifications) 
    }) 
    .catch(function(reason) { 
     console.log('Manejar promesa rechazada (' + reason + ') aquí.'); 
    }); 
}) 
.then(function(response){ 
    var secondResponse = response + '2'; 
    return response; 
}) 
.then(function(secondResponse){ 
    ...  
}) 
.catch(function(err){ 
    console.log(err)  
}) 

UPDATE

我认为这会做你所要完成

var notifications = []; 

var pMain = new Promise(function(resolve, reject) { 
    var query = 'SELECT followed_by FROM "relations" WHERE follower=' + "'" + 32 + "'" 
    dbp.sendDBRequest(query, 'blabla', function(result) { 
    resolve(result); 
    }) 
}); 

pMain.then(function(p1Result) { 
    var promises = []; 

    p1Result.forEach(function(item) { 
    return promises.push(new Promise(function(resolve, reject) { 
     var query2 = 'SELECT user_id,action,date,element_refered FROM "notifications" WHERE user_id=' + "'" + item.followed_by + "'" 
     dbp.sendDBRequest(query2, 'blabla', function(results) { 
     resolve(results); 
     }); 
    }));  
    }); 
    return Promise.all(promises).then(function(results) { 
    notifications.push(results); 
    }).then(function(){ 
    console.log(notifications); 
    }); 
}) 

什么