如何使數據庫調用，而不會丟失？

Question

由於數據庫本身是一個單獨的對象，調用它，我失去this

var neo4j = require('neo4j'); 
var db = new neo4j.GraphDatabase('http://localhost:7474'); 

function MyObject(id){this.id = id} 
MyObject.prototype.myQuery = function(){ 
    db.query('Some Query',{args:params},function(callback){ 
     //this in here is some neo4j db related object. 
     //instead of MyObject 
     console.log(this.id); //undefined 
    }); 
} 
myObject = new MyObject(9); 
myObject.myQuery(); //undefined 

任何解決方法，以使數據庫調用，還有我的this從DB的回調裏面指的是原來預期的目標？在調用之前

Answer 1

除了它保存到一個變量，你也可以如下所示結合this的功能：

MyObject.prototype.myQuery = function(){ 
    db.query('Some Query',{args:params},function(callback){ 
     //this in here is some neo4j db related object. 
     //instead of MyObject 
     console.log(this.id); //undefined 
    }.bind(this)); 
} 

...或者使用箭頭功能從ES6，儘管它還不是一個選項...

Answer 2

緩存它：

MyObject.prototype.myQuery = function(){ 
    var self = this; 
    db.query('QUERY',{args:params},function(callback){ 
     //If you use self here, it will work. 
     console.log(self.id); 
    }); 
} 

Answer 3

在調用db.query方法之前，您可以保存this，如下所示：

MyObject.prototype.myQuery = function(){ 
    var thisQuery = this; 
    db.query('QUERY',{args:params},function(callback){ 
    // Now you can use thisQuery to refer to your query object 
    } 
}