MongoDB學習筆記

時間 2019-11-09

原文原文鏈接

MongoEngine 基本命令

‘$set’: replace the value of a field with the specified value 更新新的valuepython

假設咱們有一個 products collection, 其中的字段以下正則表達式

{
  _id: 100,
  sku: "abc123",
  quantity: 250,
  instock: true,
  reorder: false,
  details: { model: "14Q2", make: "xyz" },
  tags: [ "apparel", "clothing" ],
  ratings: [ { by: "ijk", rating: 4 } ]
}

db.products.update(
   { _id: 100 },
   { $set:
      {
        quantity: 500,
        details: { model: "14Q3", make: "xyz" },
        tags: [ "coats", "outerwear", "clothing" ]
      }
   }
)

須要使用.進行修飾的mongodb

設定內嵌文檔的字段

db.products.update(
   { _id: 100 },
   { $set: { "details.make": "zzz" } }
)

設定數組內部元素的字段

db.products.update(
   { _id: 100 },
   { $set:
      {
        "tags.1": "rain gear",
        "ratings.0.rating": 2
      }
   }
)

'$and': 邏輯與符號express

用法: { $and : [ {<expression1>}, {<expression2>}, ... {<expressionN>}]}

$or: 邏輯或符號數組

用法: { $or : [ {<expression1>}, {<expression2>}, ... {<expressionN>}]}

多重判斷的寫法網絡

db.inventory.find( {
    $and : [chaxun
        { $or : [ { price : 0.99 }, { price : 1.99 } ] },
        { $or : [ { sale : true }, { qty : { $lt : 20 } } ] }
    ]
} )

CRUD 命令app

Create:
Retrieve:
Update: Supplier.update({'id': mer_supplier.id}, {'$set': {'bound_status': mer_supplier.bound_status}})
Delete:ide

正則表達式

直接給出字符, 就是精確匹配,
\d 匹配數字
\w 匹配一個字母或數字
\s 匹配空格
00\d 匹配 007
. 能夠匹配任意字符
* 表示任意個字符(0個或0個以上)
+ 表示至少一個字符
? 表示0個或1個字符
{n} 表示n個字符
{n, m} 表示n-m個字符
| 表示或關係
[] 表示範圍 [0-9] 數字0-9, [0-9a-z]數字0到9以及字母a到字母z均可以匹配url

https://www.liaoxuefeng.com/wiki/001374738125095c955c1e6d8bb493182103fac9270762a000/001386832260566c26442c671fa489ebc6fe85badda25cd000
{"$regex":r"[0-9a-z]{24}"}spa

"_id": 
"text": 
"entities": {
    "user_mentions": [
        {
            "screen_name": : "",
            ...
        }
    ],
    "urls": [],
    "hashtags": []
},
"user「: {
    "friends_count" : 544,
    "screen_name": "",
    "follwers_count" : 100,
    ...
},

MongoDB Aggregation

$group :
Example: Who Tweeted Most?
Answer:
* Group tweets by user
* Count each user's tweets
* Sort into descending order
* Select user at top

def most_tweets():
    result = db.tweets.aggregate([
                        { "$group" : {"_id" : "$user.screen_name",
                                            "count" : { "$sum" : 1 } } } , # 合併全部_id 名字爲 user.screen_name的字段,並在每次遇到一樣字段的時候加一
                         { "sort" : { "count" : -1 } } ] )
    return result

$project*: shape documents you receive as input into what you need for the next stage *$match: filter the document，選出想要的document
* Example Question: Who has the highest followers to friends ratio?

def highest_ratio():
    result = db.tweets.aggregate([
        { "$match" : { "user.friends_count" : {"$gt" : 0},
                              "user.followers_count" : {"$gt" : 0 } } },
        { "$project" : { "ratio" : { "$divide" : ["$user.followers_count", "$user.friends_count"]},
                               "screen_name" : "$user.screen_name"} },
        { "$sort" : { "ratio" : -1 } },
        { "$limit" : 1 } ])

    return result

$skip*: 直接跳過某些document, *$limit: 和skip做用相反, 直接劃定向下繼續傳入的文檔數量
$unwind: 把數組的元素抽離出來, 方便根據數組元素的來進行聚合等進一步操做
Example Question: Who included the most user mentions?

def user_mentions():
    result = db.tweets.aggregate([
                    { "$unwind" : "$entities.user_mentions" },
                    { "$group" : { "_id" : "$user.screen_name",
                                         "count" : { "$sum" : 1 } } },
                    { "$sort" : { "count" : -1 } },
                    { "$limit" : 1 } ] )

    return result