查询集合而不在猫鼬中传递模式 [英] querying a collection without passing schema in mongoose

问题描述

我是否正确理解，如果我要查询集合，我必须执行以下操作:

Do i understand correctly, that if i want to query a collection, i have to do the following:

    var mongoose = require("mongoose");

mongoose.connect();

var db = mongoose.connection;

db.on('open', function callback () {

    var kittySchema = mongoose.Schema({
        name: String
    })

    var Kitten = mongoose.model('Kitten', kittySchema)


    Kitten.find(function (err, kittens) {
        console.log(kittens);
    })

});

即使已经有很多小猫，我是否也必须每次都指定模式吗?

Do i have to specify the schema each and every time, even when there is already a collection of kittens?

为什么我不能做类似db.Kittens.find()的事情?

Why can't i do something like db.Kittens.find()?

推荐答案

在Mongoose主页上:

From the Mongoose home page:

猫鼬提供了一个简单的，基于模式的解决方案，用于 为您的应用程序数据建模，并包括内置类型转换， 验证，查询构建，业务逻辑挂钩等等 框.

Mongoose provides a straight-forward, schema-based solution to modeling your application data and includes built-in type casting, validation, query building, business logic hooks and more, out of the box.

猫鼬无法从一组可能唯一的文档中推断出一个架构. MongoDB不会对存储在集合中的文档强制执行架构.

Mongoose cannot infer from a collection of potentially unique documents a schema. MongoDB doesn't enforce schema upon the documents that are stored in a collection.

因此，Mongoose在NodeJS本机驱动程序(此处)上增加了一层，使很多人发现它们更有生产力.使用Node.JS时，并不需要与MongoDB一起使用.

So, Mongoose adds a layer upon the NodeJS native driver (here) that many find more productive. It's not a requirement to use though with MongoDB when using Node.JS.

猫鼬从根本上需要两件事:

Mongoose needs two things fundamentally to work:

1. Schema ==这定义了文档结构(参考).您可以添加验证，新方法，添加虚拟属性，使用引用.
2. Model ==这是一个类，然后在运行时用于对集合表达查询(参考).模式定义用于构建模型.

1. Schema == this defines the document structure (reference). You can add validation, new methods, add virtual properties, use data types, establish references to other collections (models).
2. Model == this is the class that is then used at run time to express queries against collections (reference). A Schema definition is used to build a Model.

因此，正如您在粘贴的样本中看到的那样，定义了小猫Schema，然后创建了Model Kitten.使用模式和模型的好处是，Mongoose会强制使用可用的属性/字段.

So, as you saw in the sample you pasted, there is a kitten Schema defined, and then a Model Kitten is created. What's nice about using a schema and model is that Mongoose then enforces the properties/fields that are available.

您只能在应用程序中定义一次Schema和Model.因此，通常在应用程序启动时，您需要执行代码来定义它们，然后在整个应用程序生命周期中根据需要使用Model实例.

You only define the Schemas and Models once in an application. So, usually as the application starts, you'll need to execute code to define them, and then use the Model instances as needed throughout the application life-cycle.

您还有更多可能想要使用Mongoose的原因.

There are many more reasons you'd want to use Mongoose potentially.

但是，您绝对是对的，您可以使用更直接的方法，而无需使用NodeJS本机驱动程序的模式.语法与您显示的语法相似，但是更加复杂:

You're absolutely right though, you could just use something more direct, without a schema by using the NodeJS native driver. The syntax would be similar to what you showed, but a bit more complex:

MongoClient.connect("mongodb://localhost:27017/exampleDb", function(err, db) {
  if(err) { return console.dir(err); }

  var collection = db.collection('kittens');

    collection.find().toArray(function(err, kittens) {
        // here ...
    });    
});

不是简单的:

Kitten.find(function(err, kittens) {

});

此外，在使用Mongoose时，您可能会发现编写更复杂的查询更容易编写和阅读:

Plus, when using Mongoose, you may find that writing more complex queries is easier to write and read:

Kitten.find().where('name', 'Harold').exec(/*callback*/);

我建议您通读更多文档，以更好地了解该框架以及该框架是否适合您的需求.不幸的是，文档有些分散，但是如果您浏览Guide标题的子标题，将会有很多有用的信息.

I'd suggest reading through more of the documentation to get a better feel for the framework and whether it's a good match for your needs. The documentation is a bit scattered about unfortunately, but if you go through the sub headings of the Guide heading, you'll have a lot of good information available.

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