猫鼬：是否可以在数组类型的字段上使用填充到 return 只有 X 个该数组的元素？

Question

我有这个型号：

const UserSchema = new Schema({
  following: [
    {
      type: Schema.Types.ObjectId,
      ref: "users",
    },
  ],
});

module.exports = User = mongoose.model("users", UserSchema);

我想在 following 字段上使用 populate，但是 return 只有该数组的前 5 个元素。

是否可以直接使用 populate 执行此操作？

我知道我最近可以在获取所有数组元素后进行此数组截断。但是，我正在做的是一个复杂的查询，我不想让它进一步复杂化。
谢谢。

Answer 1

https://mongoosejs.com/docs/populate.html#limit-vs-perDocumentLimit

Populate does support a limit option, however, it currently does not limit on a per-document basis for backwards compatibility. For example, suppose you have 5 following:

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如果你想获得 总共 5 following 而不管用户数量

const users = await User.find().populate({
  path: 'following',
  options: { limit: 5 }
});

That's because, in order to avoid executing a separate query for each document, Mongoose instead queries for fans using numDocuments * limit as the limit. If you need the correct limit, you should use the perDocumentLimit option (new in Mongoose 5.9.0). Just keep in mind that populate() will execute a separate query for each story, which may cause populate() to be slower.

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如果您希望每个用户总共获得 5 个关注

告诉 Mongoose 执行单独查询的特殊选项对于每个 User 以确保我们为每个用户获得 5 following。

const users = await User.find().populate({
  path: 'following',
  options: { perDocumentLimit: 5 }
});

猫鼬：是否可以在数组类型的字段上使用填充到 return 只有 X 个该数组的元素？

Mongoose: Is it possible to use populate on a field of type array to return only X number of elements of that array?

orm

mongoose

mongodb

node.js

mern

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