如何在不丢失数据库的情况下进行数据库调用？

Question

由于数据库本身是一种单独的对象，调用它，我失去了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

任何解决方法，以使数据库调用，还有我this是指从数据库的回调里面原来的预期目标？

Answer 1

在调用之前将其缓存：

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 2

除了将其保存到一个变量，你也可以绑定this如下所示的功能：

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));
}

...或使用ES6中的箭头功能，即使这不是一个选择...

Answer 3

您可以保存this调用之前db.query方法，就像这样：

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
  }
}