wongyouth/mongo-memo.md

## mongo-memo.md

      
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              mongo-memo.md
            
          
    Mongodb

Mongo Console Shell

db.coll.find().forEach(doc => {})
loop all documents and update

db.coll.find().forEach(doc => {
// ... change doc
// update
db.coll.save(doc)
})
nodejs code

db.coll.find().forEach(doc => {}, (err, result) => {})
删除列表中的键值

误操作增加了key键后，如何删除所有words 中的 key 键

db.lesson.find({'words.key': {$exists: true}}).forEach(doc => {
...   doc.words.forEach(word => {
...     delete word.key
...   })
...
...   db.lesson.save(doc)
...  })

$ 只匹配第一个找到的元素，所以以下这个做法达不到效果
db.lesson.updateMany({'words.key': ''}, {$unset: {'words.$.key': 1}})
匹配技巧

只打印匹配的元素

只打印 words 列表里 sound 含有单引号的文档，不显示不含单引号的word
db.lesson.find({"words.sound": {$regex:  "'"}}, {words: {$elemMatch: {sound: {$regex: "'"}}}})
{ "_id" : ObjectId("5930c492a09e1dfceff2ebb0"), "words" : [ { "word" : "can't", "sound" : "/upload/sound/can't.mp3", "mp3_url" : "http://word.kingsunsoft.com/upload/sound/can't.mp3", "phonogram" : "/kænt/", "acceptation" : "
aux. （ =can not）不能 " } ] }
{ "_id" : ObjectId("5930c4eca09e1dfceff2ec0a"), "words" : [ { "word" : "don't", "sound" : "/upload/sound/don't.mp3", "mp3_url" : "http://word.kingsunsoft.com/upload/sound/don't.mp3", "phonogram" : "/dəʊnt/", "acceptation" : "aux. (=do not) 不是；不要；不做，不干" } ] }
{ "_id" : ObjectId("5930c504a09e1dfceff2ec22"), "words" : [ { "word" : "don't", "sound" : "/upload/sound/don't.mp3", "mp3_url" : "http://word.kingsunsoft.com/upload/sound/don't.mp3", "phonogram" : "/dəʊnt/", "acceptation" : "aux. (=do not) 不是；不要；不做，不干" } ] }
{ "_id" : ObjectId("5930c50fa09e1dfceff2ec2d"), "words" : [ { "word" : "doesn't", "sound" : "/upload/sound/doesn't.mp3", "mp3_url" : "http://word.kingsunsoft.com/upload/sound/doesn't.mp3", "phonogram" : "/ˈdʌznt/", "acceptation" : "aux./v. （ =does not）不做，不干" } ] }
{ "_id" : ObjectId("5930c57ba09e1dfceff2ec95"), "words" : [ { "word" : "don't", "sound" : "/upload/sound/don't.mp3", "mp3_url" : "http://word.kingsunsoft.com/upload/sound/don't.mp3", "phonogram" : "/dəʊnt/", "acceptation" : "aux. (=do not) 不是；不要；不做，不干" } ] }
https://stackoverflow.com/questions/3985214/retrieve-only-the-queried-element-in-an-object-array-in-mongodb-collection
列表元素数量大于1的所有文档


db.lesson.aggregate( [
...   { $project: {words: 1} },
...   { $match: {words: {$ne: null}} },
...   { $unwind : "$words" },
...   { $group : { _id : "$words.sound", words: {$addToSet: "$words.word"} } },
...   { $project: { words: 1, count: {$size: '$words' }}},
...   { $match: {count: {$gt: 1}}}
... ])

如果不在aggregate 中，还可以使用 $where
db.lesson.find({$where: 'this.words.length > 1'})
https://stackoverflow.com/questions/7811163/query-for-documents-where-array-size-is-greater-than-1


搜索未设置字段
  db.lesson.find({words: {$exists: false}})


搜索有设置字段
  db.lesson.find({words: {$exists: true}})


搜索字段为null
  db.lesson.find({words: null}).count()


搜索字段不为null
  db.lesson.find({words: {$ne: false}})


搜索字段数组长度为0
  db.lesson.find({words: {$size: 0}})


搜索字段数组长度大于0
  db.lesson.find({$where: 'this.words.length > 0'})