MongoDB C100DEV 2.CRUD

版权信息

• 本文为CSDN 博主luopotaotao原创,转载请注明出处
• 欢迎加群交流探讨 218368963【MongoDB C100DEV】

CRUD

这部分是重点,有十几二十来题吧

实际考试中,重点有

• 语法的检查
• 数组的查询
• 带multi,upsert选项的update操作
• 比较操作符(会明确给出是gt,lt还是gte,lte,不会有边界模糊的情况)
• 条件结合in,and,$or
• skip和limit

需要具备:

• 明白MongoDB的crud语言
• 熟悉并掌握常用的CRUD操作
• 知道MongoDB支持哪些数据类型
  考试不检查语法的记忆,但是需要能够分辨出给定查询的正确性.
  也要知道哪些查询参数是必要的,哪些是可选的,如何使用这些参数

Create

• 正确的使用insert,save,update,findAndModify命令创建新的文档
• 给出 insert 命令,指出其具体做了些什么
• 如何执行批量插入
• 理解_id字段的唯一性限制及其在CURD中的含义
• 理解ObjectIds如何创建和使用

Read

• 正确的使用query,projection和可选参数
• 排序查询结果
• 所有的match和projection操作符
• 读译正则表达式查询
• 查询数组

Update

• 正确的使用save,update,findAndModify命令修改存在的文档
• 这句话不明白
  Distinguish which parameter finds the documents to change, which mutates them
• 解释update操作符的行为
• 识别什么时候upserts和db.collections.save()将会插入新的文档

Delete

• 删除集合
• 构建删除命令来删除指定文档

问题示例

1.Consider the following documents:

{ "_id" : 1, "a" : 1, "b" : 1 }{ "_id" : 2, "a" : 2, "b" : 3 }{ "_id" : 3, "a" : 3, "b" : 6 }{ "_id" : 4, "a" : 4, "b" : 10 }{ "_id" : 5, "a" : 5, "b" : 15 }You perform the following query:db.stuff.update( { b : { $gte : 10 } },                 { $set : { b : 15 } },                 { multi : true, upsert : true } )How many documents will be updated by the query?a.0b.1c.2d.3e.5

2.Consider the following document:

> db.c.find(){ "_id" : 12, b : [ 3, 5, 7, 2, 1, -4, 3, 12 ] }Which of the following queries on the "c" collection will return only the first five elements of the array in the "b" field? E.g.,Document you want returned by your query:{ "_id" : 12, "b" : [ 3, 5, 7, 2, 1 ] }a.db.c.find( { } , { b : [ 0, 1, 2, 3, 4, 5 ] } )b.db.c.find( { } , { b : [ 0 , 5 ] } )c.db.c.find( { } , { b : { $slice : [ 0 , 5 ] } } )d.db.c.find( { } , { b : { $substr[ 0 , 5 ] } } )e.db.c.find( { b : [ 0 , 5 ] } )

3.Consider the following example document from the sample collection.
All documents in this collection have the same schema.

{  "_id" : 3,  "a" : 7,  "b" : 4}Which of the following queries will replace this with the document,{  "_id" : 7,  "c" : 4,  "b" : 4}a.db.sample.update( { "_id" : 3 } , { "_id" : 7 , "c" : 4 } )b.db.sample.update( { "_id" : 3 } , { "$set" : { "_id" : 7 , "c" : 4 } } )c.db.sample.update( { "_id" : 3 } , { "_id" : 7 , "c" : 4 , { "$unset" : [ "a" , "b" ] } } )d.db.sample.update( { "_id" : 3 } , { "_id" : 7 , "c" : 4 } , { "justOne" : true } )e.This operation cannot be done with a single query.

4.Which of the documents below will be retrieved by the following query?
Assume the documents are stored in a collection called “sample”. Check all that apply.
db.sample.find( { “or" : [ { "a" : { "in" : [ 3, 10] } }, { "b" : { "$lt” : 2 } } ] } )

a. { "_id" : 1, "a" : 0, "c" : 0, "b" : 2 }b. { "_id" : 2, "a" : 2, "c" : 0, "b" : 1 }c. { "_id" : 3, "a" : 4, "c" : 0, "b" : 14 }d. { "_id" : 4, "a" : 5, "c" : 0, "b" : 17 }e. { "_id" : 5, "a" : 3, "c" : 0, "b" : 12 }f. { "_id" : 6, "a" : 1, "c" : 1, "b" : 5 }g. { "_id" : 7, "a" : 8, "c" : 1, "b" : 7 }h. { "_id" : 8, "a" : 11, "c" : 1, "b" : 0 }i. { "_id" : 9, "a" : 17, "c" : 1, "b" : 1 }j. { "_id" : 10, "a" : 3, "c" : 1, "b" : 1 }You perform the following operation in the shell:db.foo.insert( { } );What gets inserted?a.An empty documentb.A document with an _id assigned to be an ObjectIdc.A document that matches the collection's existing schema, but with null fieldsd.No document will be inserted; an error will be raisede.A document will be inserted with the same _id as the last document inserted

Answers to Sample Problems

1.b2.c3.e4.b, e, h, i, j5.b

例题(大概意思和方向,非原题)

1.集合coll中有以下文档,执行db.coll.update({a:{$gte:5}},
{$set:{b:15}},
{multi:true,upsert:true})

    a. {_id:id0,a:1,b:3}       b. {_id:id1,a:5,b:5}    c. {_id:id2,a:10,b:15}    问题1:哪些文档被查询到 b,c    问题2:有多少条记录会被插入 0 因为查询到了记录,upsert选项不做插入操作    问题3:有多少条记录会被更新 1 因为c中b的值就是15,因此不会被更新

2.集合中以下内容,执行查询db.coll.find({a:{$gte:5}},{b:1,_id:0}),

    a. {_id:id0,a:1,b:3}    b. {_id:id1,a:5,b:5}    c. {_id:id2,a:10,b:15}    c. {_id:id3,a:10,b:[3,15,20]}    哪些记录会被查询到 b,c,d     主要考察b字段既有数字,又有数组时的查询和投影选项