为什么我通常会在“容器”数据类型中看到数据，例如在 object 中看到数据，在 object 中看到数组？

Question

I have dangerously little actual programming experience, but when I delve into the data of actual coders I often encounter something like this and I don't understand why...

(from a little ditty I was working on in javascript this weekend)

{
  "data": [
    {
      "name": "foo",
      "id": 0
    },
    {
      "name": "bar",
      "id": 1
    },
    {
      "name": "baz",
      "id": 2
    },
  ]
};

That's an object with a single key:value where the key is "data" and the value is an array, and the array is a list of objects inside each is a name and an ID.

It seems to me there's at least one extra layer of abstraction inside here. Why not have Just the array of object? Why have the outer object with one element? I figure there's got to be a good reason, but it seems like it just makes it more difficult to access the data within.

Answer 1

Say one of your coders implemented the endpoint GET /users which returned an array of users

[
  { id: 0, name: 'foo' },
  { id: 1, name: 'bar' },
  { id: 2, name: 'baz' },
] // <- the response body of GET /users

This is good for a while. Then, your userbase starts getting large, and you realize you have to start paginating the endpoint with limit and offset to avoid overloading clients. How would you track the last offset ?

You'll typically find response payloads like the one in your example to allow for this:

{
  "data": [
    {
      "name": "foo",
      "id": 0
    },
    {
      "name": "bar",
      "id": 1
    },
    {
      "name": "baz",
      "id": 2
    },
  ],
  offset: 200
};

You could then scale your userbase without worry.