node.js 如何在 Mongoose 中查询不同的值？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/6043847/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How do I query for distinct values in Mongoose?
提问by Kit Sunde
I have a problem where I want to be able to get all the unique cities for a collection, and my code looks something like this:
我有一个问题，我希望能够获得一个集合的所有独特城市，我的代码如下所示：
var mongoose = require("mongoose"),
Schema = mongoose.Schema;
var PersonSchema = new Schema({
name: String,
born_in_city: String
});
var Person = mongoose.model('Person', PersonSchema);
In native MongoDb I could just do db.person.distinct("born_in_city"), but there doesn't seem to be anything equivalent for Mongoose. Is the only option to iterate over all of the documents myself to do this, or is there a better solution?
在本机 MongoDb 中，我可以做db.person.distinct("born_in_city")，但似乎没有任何与 Mongoose 等效的东西。是自己迭代所有文档来执行此操作的唯一选择，还是有更好的解决方案？
In an attempt to use the underlying node-mongodb-nativeas suggested by the answerer I attempted to do this:
为了node-mongodb-native按照回答者的建议使用底层，我尝试这样做：
mongoose.connection.db.collections(function(err, collections){
collections[0].distinct('born_in_city', function( err, results ){
console.log( err, results );
});
});
However the resultsis empty and there's no error. I would also prefer to be able to fetch only the needed collection by name rather than have to filter what collectionsreturn if at all possible.
然而，results是空的，没有错误。我还希望能够仅按名称获取所需的集合，而不必尽可能过滤collections返回的内容。
回答by Risadinha
Just to give an update for Mongoose 3.x:
只是为了提供 Mongoose 3.x 的更新：
MyModel.find().distinct('_id', function(error, ids) {
// ids is an array of all ObjectIds
});
回答by yshgt
In my program, this code works.
在我的程序中，此代码有效。
Person.collection.distinct("born_in_city", function(error, results){
console.log(results);
});
by node.js v0.4.7, mongoose 1.3.3
通过 node.js v0.4.7，猫鼬 1.3.3
回答by Bryan
I read through the source code and the node-mongodb-native driver is what powers the class. So on the connection object. So after you have done mongoose.connect(mongodb://), you can give this a shot.
我通读了源代码，node-mongodb-native 驱动程序是类的动力。所以在连接对象上。所以在你完成 mongoose.connect(mongodb://) 之后，你可以试一试。
if(mongoose.connections.length > 0) {
var nativeconn = mongoose.connections[0].conn;
nativeconn.person.distinct('born_in_city', function(error, results){
});
}
