mongo学习笔记

2019/03/18 技术

mongo学习笔记

1. mongo document学习笔记

1.1 BSON 类型

  • ObjectId: 快速, 有序, 时间相关
  • String
  • Timestamps
  • Date

1.2 Document类型

  • 字段(field)有长度限制: 如field name不超过128, 等
  • Dot Notation: <array>.<index>, <embedded document>.<field>
  • 单文档有大小限制:16MB

1.3 聚合

MongoDB provides three ways to perform aggregation: the aggregation pipeline, the map-reduce function, and single purpose aggregation methods.

聚合字段:

  • $match: 匹配, { $match: { name: "Joe Schmoe" } }
  • unwind: 打散,针对array, { $unwind: "$resultingArray"}
  • $project: 投射, {"$project":{"author":1,"_id":0} #只提前author
  • $redact: 校验, { $redact: { $cond: { if: { $eq: [ "$level", 5 ] }, then: "$$PRUNE", else: "$$DESCEND" } } }
  • $skip: 跳过, { $skip: 5 }
  • $lookup: 跨表检索, { $lookup: { from: "otherCollection", as: "resultingArray", localField: "x", foreignField: "y" } }

Note:

  • 各字段配合的优化, 参考文档

聚合限制:

  • Result Size Restrictions: 单doc <= 16MB
  • Memory Restrictions: Pipeline stages have a limit of 100 megabytes of RAM; The $graphLookup stage must stay within the 100 megabyte memory limit.

todo: 聚合操作zip code data set(经纬度)

Aggregation with User Preference Data, 利用用户信息表举例:

  • 获取所有员工名称
  • 根据加入时间返回员工名称
  • 获取每个月新加入的人数
  • 获取前五个最受欢迎的爱好

1.4 检索

条件检索

  • $or: cursor = db.inventory.find({"$or": [{"status": "A"}, {"qty": {"$lt": 30}}]})
  • $and

检索列表:

  • Match an Array: db.inventory.find({"tags": ["red", "blank"]}) # tags == ["red", "blank"]; db.inventory.find({"tags": {"$all": ["red", "blank"]}}) # tags 同时存在"red","blank"两个元素
  • Query an Array with Compound Filter Conditions on the Array Elements: db.inventory.find({"dim_cm": {"$gt": 15, "$lt": 20}}) # 15<x<20; x>15, y<20
  • Query for an Array Element that Meets Multiple Criteria: db.inventory.find({"dim_cm": {"$elemMatch": {"$gt": 22, "$lt": 30}}}) # 其中有一个元素22<x<30
  • Query for an Element by the Array Index Position: db.inventory.find({"dim_cm.1": {"$gt": 25}})
  • Query an Array by Array Length: db.inventory.find({"tags": {"$size": 3}})

Project:

  • db.inventory.find({"status": "A"}, {"item": 1, "status": 1}) means SELECT _id, item, status from inventory WHERE status = "A"
  • db.inventory.find({"status": "A"}, {"item": 1, "status": 1, "_id": 0}) means SELECT item, status from inventory WHERE status = "A"
  • db.inventory.find({"status": "A"}, {"status": 0, "instock": 0}) means return All except for status and instock

其他

  • db.inventory.find({"item": None}): None 或 不存在
  • db.inventory.find({"item": {"$type": 10}}): 类型检查, 查询值为None的记录
  • db.inventory.find({"item": {"$exists": False}}): 不存在

1.5 固定集合(Capped Collection)

  • 判断当前集合是否是固定集合: db.collection.isCapped()
  • 转化为固定集合(原数据可能会丢失): db.runCommand({"convertToCapped":"my_coll",size:2000000000, max:500000}). max 为文档数量, size 为内容大小

2.聚合操作

2.1 获取列表元素集合

keywords: group, unwind, aggregate

举例,有如下数据:

{"_id": "1", "tags": ["a", "b"]}
{"_id": "2", "tags": ["a", "b", "c"]}
{"_id": "3", "tags": []}
{"_id": "4", "tags": ["c", "d"]}

求tags元素集合?

方法:

db.test.aggregate([
    {"$unwind": "$tags"},
    {"$group": {"_id": "$tags"}},
])

2.2 获取某个字段的所有取值

db.getCollection('<collection>').aggregate(
   [
     { "$group" : { _id : null, "city": { "$addToSet": "$city" } } }
   ]
)

3.update操作

3.1 修改列表元素的值

keywords: update_many

举例,有如下数据:

{"_id": "1", "tags": ["a", "b"]}
{"_id": "2", "tags": ["a", "b", "c"]}
{"_id": "3", "tags": []}
{"_id": "4", "tags": ["c", "d"]}

tags中”a”修改为”A”?

方法:

self.db["test"].update_many(
    filter={"tags": "a"},
    update={"$set": {'tags.$': "A"}},
    upsert=False,
    )
    
# 一次操作只能修改一个值
# 如果tags中存在多个"a", 需要多次执行以上代码

3.2 删除列表元素的值

keywords: update_many

举例,有如下数据:

{"_id": "1", "tags": ["a", "b"]}
{"_id": "2", "tags": ["a", "b", "c"]}
{"_id": "3", "tags": []}
{"_id": "4", "tags": ["c", "d"]}
{"_id": "5", "tags": ["c", "d", "a", "a"]}

tags中所有”a”删除?

方法:

tag_list = ["a"]
self.db["test"].update_many(
    filter={"tags": {"$in": tag_list}},
    update={"$pull": {'tags': {"$in": tag_list}}},
    upsert=False,
)
# 执行后, _id = "5"的记录, tags中两个"a"均被删除

3.3 列表修改高级版

假设有数据如下

collection.insert_many([
{"name": "a1", "tags": [{"weight": 10}, {"weight": 20}]},
{"name": "a2", "tags": [{"weight": 11}, {"weight": 21}]},
{"name": "a3", "tags": [{"weight": 10}, {"weight": 25}]},
])

3.3.1 将weight=10的标签的权重更改为20

# 执行一次,只会更新该条记录中满足条件的第一个元素

collection.update_many(
{"tags.weight": 10},
{"$set": {"tags.$.weight": 20}},
upsert=False,
)

修改所有匹配值的方法:

while True:
    result = collection.update_many(
                {"tags.weight": 10},
                {"$set": {"tags.$.weight": 20}},
                upsert=False,)
    if result.matched_count == 0:
        break

3.3.2 将weight!=10的标签的权重更改为10

# 执行一次,只会更新该条记录中满足条件的第一个元素

collection.update_many(
{"tags": {"$elemMatch": {"weight": {"$ne": 10}}},
{"$set": {"tags.$.weight": 20}},
upsert=False,
)

3.3.3 将weight!=10 or weight!=20的标签的权重更改为10

# 执行一次,只会更新该条记录中满足条件的第一个元素

collection.update_many(
{"tags": {"$elemMatch": {"$or": [{"weight": {"$ne": 10}, {"weight": {"$ne": 20}]}}},
{"$set": {"tags.$.weight": 20}},
upsert=False,
)

3.4 set only not exists

mongo 提供 $setOnInsert 操作符, 来实现当文档不存在才设置的功能。

db.collection.update(
   <query>,
   { $setOnInsert: { <field1>: <value1>, ... } },
   { upsert: true }
)

4. 工具

4.1 导出 collection

mongoexport --uri "mongodb://<username>:<password>@<host1>:<port1>,<host2>:<port2>/<database>?replicaSet=mgset-123456&authSource=admin" --collection <collection> --fields <field1>,<field2> --out <outfile>

要点:

  • uri后加引号, admin放到authSource

或者:

mongoexport -h <host> -d <databse> --collection <collection> --fields <field1>,<field2> --out <outfile>

4.2 导入 collection

mongoimport --uri "mongodb://<username>:<password>@<host1>:<port1>,<host2>:<port2>/<database>?replicaSet=mgset-123456&authSource=admin" --collection <collection> --fields <field1>,<field2> <datafile>

或者

mongoimport -h <host> -d <databse> --collection <collection> --fields <field1>,<field2> <datafile>

4.3 索引操作

新建索引:

db.getCollection('<collection>').createIndex( { "age": 1}, {background: true, name:"_age_"} )

4.4 mongo 版本不兼容

mongo 升级到 4.0 版本后,其工具如mongodump, mongoimport, mongoexport也需要升级到 4.0版本。

为避免安装这些工具导致主机软件环境混乱,可以使用 docker 执行所需的工具。

# download images
docker pull mongo:4.0

# mkdir working dir
mkdir -p dodo && chmod 777 dodo/ -R && cd dodo/

# run mongo tools
docker run --rm -v $(pwd):/workdir/ -w /workdir/ mongo:4.0 mongoimport --uri "mongodb://<username>:<password>@<host1>:<port1>,<host2>:<port2>/<database>?replicaSet=mgset-123456&authSource=admin" --collection <collection> --fields <field1>,<field2> <datafile>

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