文档中的空字段是否占用Mongoose中的空间？ [英] Do empty fields in a document take up space in Mongoose?

问题描述

我不考虑使用继承或引用，而是考虑用所有可能的字段定义一个模式。因此，模式将有许多字段，其中一些将大多数时间是空的。空字段仍然占用数据库中的空间？我应该定义单独的模式吗？

解决方案

由于你使用Mongoose，答案涉及很多细微差别。 Mongoose将根据字段的类型做各种事情。如果您定义 类型的字段例如

  {
 name：String，
 age：Number 
} 
  

其中名称和年龄都不是必填字段。一旦你调用创建只有名称例如

  model.create {name：'Yuri'}）
  

然后在数据库中， name defined

{_ id：ObjectId（'....'），name：'Yuri'}

换句话说，mongoose不会存储年龄。

但另一方面，如果你有一个字段被声明为数组，例如

  {
 name：String，
 ages：[] 
} 
  

然后，如果你执行相同的 create 调用如上，它将导致以下文档：

  {_ id：ObjectId（'...'），name：'Yuri'，ages：[]} 
  / pre> 
 
 
换句话说，即使你在创建调用中没有指定 ages ，mongoose你的数组。 
 
 
 
 TLDR：如果你的模式是平的，只由字符串和数字组成，那么mongoose不会将这些字段保存在db中，但它将用于对象和数组。
 
Instead of resorting to inheritance or references, I am thinking of defining one schema with all the possible fields. As a result, the schema will have many fields, some of which will be empty most of the times. Will the empty fields still take up space in the database? Should I define separate schemas instead?
解决方案
Since you're using Mongoose, the answer involves a lot of nuances. Mongoose will do various things depending on the type of field. If you define a field of type Number of String e.g.
{
  name: String, 
  age: Number
}
Where neither name nor age is a "required" field. Once you call create with just the name e.g.
model.create({name: 'Yuri'})
Then in your database, you will have an object with just the name defined

{_id: ObjectId('....'), name: 'Yuri' }

In other words, mongoose will not store the age. 

But on the other hand, if you have a field that is declared as an array, e.g.
{
  name: String,
  ages: []
}
Then if you perform the same create call as above, it will result in the following document:
{_id: ObjectId('...'), name: 'Yuri', ages: []}
So in other words, even though you didn't specify ages in your create call, mongoose created the array for your anyway. The same mechanics apply to nested objects.

TLDR: if your schema is flat, and is composed of just strings and numbers, then mongoose will not save those fields in the db, but it will for objects and arrays.

                        
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