如何使用Waterline和Sails.js(版本0.10)从mongo数据库中提取不同的值? [英] How to extract distinct values from a mongo database using Waterline and Sails.js (version 0.10)?

问题描述

使用Sails.js版本0.10.x，假设我有一个模型Dog，填充如下(为方便起见，以yaml格式写出，但在我的情况下，它实际上是在mongo数据库中.)

Using Sails.js version 0.10.x, assume I have a model Dog, populated as follows (writtenout in yaml format for convenience, but in my case it's actually in a mongo database.)

dogs:
-  breed: "wolf"
   name: "Fido"
-  breed: "wolf"
   name: "Roger"
-  breed: "dingo"
   name: "Nipper"
-  breed: "dingo"
   name: "Ernie"
-  breed: "corgi"
   name: "Bernadi"
-  breed: "corgi"
   name: "Queenie"
-  breed: "poodle"
   name: "Christopher"
-  breed: "poodle"
   name: "Tony"

etc

所以现在我要创建可用品种的列表.

So now I want to create a list of the available breeds.

Dog.find().exec(err, dogs) {
  breeds = [];
  dogs.each(function(dog)) {
    if (breeds.indexOf(dog.breed) === -1) breeds.push(dog.breed);
  }
  ...
}

是否有更简单的方法来减少数据库的点击次数?像

Is there a simpler way to do this with fewer hits on the database? Something like

Dog.find().distinct('breed').exec(function(err, breeds){
  ...
});

我发现了这个封闭的水线问题，这似乎表明我可以使用.distinct方法，但我尝试过，可惜没有骰子.

I've found this closed Waterline issue which seems to indicate that I could use a .distinct method but I tried it and alas no dice.

Object [object Object] has no method 'distinct'

我该如何以数据库有效的方式解决这个问题?

How might I go about this in a database efficient manner?

推荐答案

对于这类查询，您可以使用native方法执行原始的MongoDB命令:

For these kind of queries you can use use native method to execute raw MongoDB command:

Dog.native(function(err, collection) {
    collection.distinct('breed', function(err, dogs) {
        // do something here
    });
});

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