FindOptions 相關參數

• limit:筆數
• sort:排序
• projection:返回指定欄位
• skip:跳過 N 個欄位

基本使用

findOne - 單筆查詢

package 源碼

findOne<T = TSchema>(filter: Filter<TSchema>, options?: FindOptions): Promise<T | null>;

interface User {
    name: string
    age: number
    address: string
}
const collection: Collection<User> = db.collection<User>("user");
const query: Filter<User> = {
  name: 'Fred'
}
await collection.findOne(query);

find - 多筆查詢

package 源碼

find(filter: Filter<TSchema>, options?: FindOptions): FindCursor<WithId<TSchema>>;

interface User {
    name: string
    age: number
    address: string
}
const query: Filter<User> = {
  name: /F/
}
const cursor = collection.find(query);
let users = await cursor.toArray()    // 這才是回傳陣列欄位

返回指定欄位

interface User {
    name: string
    age: number
    address: string
}
const query: Filter<User> = {
  name: /F/
}
const option: FindOptions = {
  sort: { name: -1 }, // 排序
  projection: { name: true, address: true }, // 僅回傳需要的欄位，這就不會回傳 age
}
type ResultUser = Pick<Store, "name" | "address">;
const user = await collection.findOne<ResultUser>(query, option);

分頁搜尋

const req = {
  rows: 10,   // 筆數
  page: 1,    // 頁面
}

const query: Filter<User> = {
  name: /F/
}
const option: FindOptions = {
  sort: { name: -1 }, // 指定某欄位排序
  skip: req.rows * (req.page - 1),
  limit: req.rows
}
type ResultUser = Pick<Store, "name" | "address">;
const cursor = collection.find(query, option);
let users = await cursor.toArray()    // 這才是回傳陣列欄位

運算符

於Find中使用是針對 Filter<TSchema> 進行運算

比較查詢 (Comparison Query)

// Example
interface User {
    name: string
    age: number
    address: string
}
const query: Filter<User> = {
  name: {
    $eq : 'Fred'
  }
}

邏輯查詢 (Logical Query)

// Example
interface User {
    name: string
    age: number
    address: string
}
const query: Filter<User> = {
  $or : [
    {
      name: 'Fred'
    },
    {
      name: 'Leo'
    },
  ]
}

元素查詢 (Element Query)

略，目前感覺用不到

評估查詢 (Evaluation Query) - 進階

• $regex

  // Example
  interface User {
      name: string
      age: number
      address: string
  }
  const query: Filter<User> = {
      {
        name: { $regex: /F/ }
      },
  }
  

• $mod

  db.inventory.insertMany( [
    { "_id" : 1, "item" : "abc123", "qty" : 0 },
    { "_id" : 2, "item" : "xyz123", "qty" : 5 },
    { "_id" : 3, "item" : "ijk123", "qty" : 12 }
  ] )
  db.inventory.find( { qty: { $mod: [ 4, 0 ] } } )
  // { "_id" : 1, "item" : "abc123", "qty" : 0 }
  // { "_id" : 3, "item" : "ijk123", "qty" : 12 }
  

• $text

  運算符	型別	翻譯
  $search	string	查詢，這功能很好用
  $language	string	(ISO 639-1 ) 但很抱歉沒中文
  $caseSensitive	boolean	大小寫敏感，base on 語系
  $diacriticSensitive	boolean	相似音，base on 語系

  db.articles.insertMany( [
      { _id: 1, subject: "coffee", author: "xyz", views: 50 },
      { _id: 2, subject: "Coffee Shopping", author: "efg", views: 5 },
      { _id: 3, subject: "Baking a cake", author: "abc", views: 90  },
      { _id: 4, subject: "baking", author: "xyz", views: 100 },
      { _id: 5, subject: "Café Con Leche", author: "abc", views: 200 },
      { _id: 6, subject: "Сырники", author: "jkl", views: 80 },
      { _id: 7, subject: "coffee and cream", author: "efg", views: 10 },
      { _id: 8, subject: "Cafe con Leche", author: "xyz", views: 10 }
  ] )
  
  db.articles.find( { $text: { $search: "coffee" } } )
  
  // { _id: 1, subject: 'coffee', author: 'xyz', views: 50 },
  // { _id: 7, subject: 'coffee and cream', author: 'efg', views: 10 },
  // { _id: 2, subject: 'Coffee Shopping', author: 'efg', views: 5 }
  

• $where
  需將MongoDB啟用 JavaScript Enablement功能（預設即啟用），這邊先將這功能略過，若要使用 Aggregation（聚合）功能需要進行 javascript查詢 建議使用$function 代替 $where

  db.players.insertMany([
    { _id: 12378, name: "Steve", username: "steveisawesome", first_login: "2017-01-01" },
    { _id: 2, name: "Anya", username: "anya", first_login: "2001-02-02" }
  ])
  db.players.find( { $where: function() {
    return (hex_md5(this.name) == "9b53e667f30cd329dca1ec9e6a83e994")
  } } );
  // {
  //    "_id" : 2,
  //    "name" : "Anya",
  //    "username" : "anya",
  //    "first_login" : "2001-02-02"
  // }
  

• $expr
  從官網看這篇的時候，會突然資訊量爆棚一堆英文單字，expression / aggregation / stage / pipeline …
  其實可專注在，如何分辨使用 $expr / aggregate？ 這件事

  // 這是使用 aggregate 起手式
  db.collection.aggregate()
  // 這是使用 $expr 起手式
  db.collection<User>("user").find({ $expr: ... })
  

  stage / pipeline 曾經做過 CI/CD 或 webpack 優化 的過程中可以看到這英文單字，中文來說就是「階段」
  expression 就是在描述「條件」
  $expr 的條件中可以用聚合表達式查詢功能，下方為官網範例。

  db.supplies.insertMany([
   { "_id" : 1, "item" : "binder", "qty" : NumberInt("100"), "price" : NumberDecimal("12") },
   { "_id" : 2, "item" : "notebook", "qty" : NumberInt("200"), "price" : NumberDecimal("8") },
   { "_id" : 3, "item" : "pencil", "qty" : NumberInt("50"), "price" : NumberDecimal("6") },
   { "_id" : 4, "item" : "eraser", "qty" : NumberInt("150"), "price" : NumberDecimal("3") },
   { "_id" : 5, "item" : "legal pad", "qty" : NumberInt("42"), "price" : NumberDecimal("10") }
  ])
  
  // 使用聚合表達式查詢
  let discountedPrice = {
    $cond: {
        if: { $gte: ["$qty", 100] },
        then: { $multiply: ["$price", NumberDecimal("0.50")] },
        else: { $multiply: ["$price", NumberDecimal("0.75")] }
    }
  };
  
  db.supplies.find( { $expr: { $lt:[ discountedPrice,  NumberDecimal("5") ] } });
  

• $jsonSchema 略，目前感覺用不到

數組查詢 (Array Query)

總結

查詢為DB超級常見的功能，初期簡易使用即可，可專研 Evaluation Query，若是要更彈性使用，可後續網 aggregation篇章深入，官網資訊量很多