MongoDB for Java Programmer ——2
CRUD
在关系型数据库中，如果一个字段没有有效值，我们通常会初始化默认值（当然也可以存NULL），但在MongoDB中，我们可以不存储这个字段即可.这就是所谓的schema-less
Creating documents in mongodb
- db.mycoll.insertOne(document, )
- db.mycoll.insertMany( [documents], )
第二个参数如果是 “ordered”:false 则表示非顺序插入，其中某个document遇到异常，不影响其他document的插入。默认为True，顺序插入，会在错误处中断执行,则后续操作就不会执行了。
- upsert （如果存在重复的先更新，否则直接插入。这种创建document的方式不详述）
每次插入document（一条数据），这个数据必须有一个“_id”字段，默认是自动生成一个唯一的ObjectId(…)，也可以手动指定一个唯一的数据。类似于传统数据库中的自增主键。
以上所说的“唯一”是在单个个collection中唯一，类似于传统数据库表的自增主键唯一，也只是这个table中唯一。
如下实例，可以看到“_id”除了自动生成，也可以手动设置（不建议手动设置，原因看后文）。
> db.elementMatch.insertMany([{result:[82,85,88]},{result:[75,88,89]}])
{
"acknowledged" : true,
"insertedIds" : [
ObjectId("57558318c700c2881f75fef6"),
ObjectId("57558318c700c2881f75fef7")
]
}
> db.moviesScratch.insertOne({ "title": "Rocky", "year": "1976", "imdb": "tt0075
148"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5753c0eeeb62b409398b67ac")
}
> db.moviesScratch.insertOne({ "title": "Rocky", "year": "1976", "imdb": "tt0075
", "_id":"10001"})
{ "acknowledged" : true, "insertedId" : "10001" }
> db.moviesScratch.find({"title":"Rocky"}).pretty()
{
"_id" : ObjectId("5753bcd0d72e989351cbf22a"),
"title" : "Rocky",
"year" : "1976",
"imdb" : "tt0075148"
}
{
"_id" : ObjectId("5753c0eeeb62b409398b67ac"),
"title" : "Rocky",
"year" : "1976",
"imdb" : "tt0075148"
}
{ "_id" : "10001", "title" : "Rocky", "year" : "1976", "imdb" : "tt0075" }详解_id字段
默认情况下，每个collection（表）都会在“_id”字段上有一个聚簇索引（可理解为主键索引）。并且这字段的默认类型是OjbectId.
{ "_id" : ObjectId("5753e1bfeb62b409398b67c1"), ...... }
{ "_id" : ObjectId("5753e1e9eb62b409398b67c2"),......}ObjetcId是一个12byte的16进制字符串组成如下：
Reading Documents
- db.mycoll.find([query],[fields])
- query is an optional query filter. fields is optional set of fields to return.
e.g.
db.mycoll.find( {x:77} , {name:1, x:1} )
……………
db.mycoll.find(…).count()
db.mycoll.find(…).limit(n)
db.mycoll.find(…).skip(n)
db.mycoll.find(…).sort(…)
db.mycoll.findOne([query], [fields], [options], [readConcern])
- query is an optional query filter. fields is optional set of fields to return.
> db.movieDetails.find({"rated":"PG-13"}).count()
153
> db.movieDetails.find({"rated":"PG-13","year":2009}).count()
8如何选择性读取内嵌fields
{
｛....
{
"fieldOuterN": {
...,"fieldInner": value
}
}
....｝
}如果要通过内嵌结构的字段查找,比如以下document中tomato字段中的meter等字段，使用如下方式 db.mycoll.find({“fieldOuterN.fieldInner” : value，……})：
> db.movieDetails.findOne()
{
"_id" : ObjectId("569190ca24de1e0ce2dfcd4f"),
"title" : "Once Upon a Time in the West",
"year" : 1968,
"rated" : "PG-13",
"released" : ISODate("1968-12-21T05:00:00Z"),
"runtime" : 175,
"countries" : [
"Italy",
"USA",
"Spain"
],
"genres" : [
"Western"
],
..........
"tomato" : {
"meter" : 98,
"image" : "certified",
"rating" : 9,
"reviews" : 54,
"fresh" : 53,
"consensus" : "A landmark Sergio Leone spaghetti western masterp
iece featuring a classic Morricone score.",
"userMeter" : 95,
"userRating" : 4.3,
"userReviews" : 64006
},
"metacritic" : 80,
"awards" : {
"wins" : 4,
"nominations" : 5,
"text" : "4 wins & 5 nominations."
},
"type" : "movie"
}
> db.movieDetails.find({"tomato.rating":100}).count()
0
> db.movieDetails.find({"tomato.meter":100}).count()
8如何选择性读取数组类型value
一般有以下几种读取场景：
- 过滤读取 整个数组
比如，读取 “writers” 字段值为 [“Ethan Coen”, “Joel Coen”]的document.(元素顺序、个数、内容等等完全匹配)
> db.movieDetails.find({"writers":["Ethan Coen","Joel Coen"]}).pretty()
{
"_id" : ObjectId("5692a14f24de1e0ce2dfcf60"),
"title" : "The Big Lebowski",
"year" : 1998,
"rated" : "R",
"released" : ISODate("1998-03-06T05:00:00Z"),
"runtime" : 117,
"countries" : [
"USA",
"UK"
],
"genres" : [
"Comedy",
"Crime"
],
"director" : "Joel Coen, Ethan Coen",
"writers" : [
"Ethan Coen",
"Joel Coen"
],
"actors" : [
"Jeff Bridges",
"John Goodman",
"Julianne Moore",
"Steve Buscemi"
],
........................
"type" : "movie"
}- 过滤读取 数组中任一个元素
查找writers数组字段中含有 “Jeff Bridges”的所有document
> db.movieDetails.find({"actors":"Jeff Bridges"}).pretty()
{
"_id" : ObjectId("569190d124de1e0ce2dfcd86"),
"title" : "The Last Picture Show",
"year" : 1971,
"rated" : "R",
"released" : ISODate("1971-10-22T04:00:00Z"),
"runtime" : 118,
"countries" : [
"USA"
],
"genres" : [
"Drama"
],
"director" : "Peter Bogdanovich",
"writers" : [
"Larry McMurtry",
"Peter Bogdanovich",
"Larry McMurtry"
],
"actors" : [
"Timothy Bottoms",
"Jeff Bridges",
"Cybill Shepherd",
"Ben Johnson"
],
"plot" : "A group of 1950s high schoolers come of age in a bleak, isolat
ed, atrophied West Texas town that is slowly dying, both economically and cultur
ally.",
"poster" : "http://ia.media-imdb.com/images/M/MV5BNDkyNzQ1NzYzN15BMl5Ban
BnXkFtZTcwNjE5MDEwNw@@._V1._CR73.19999694824219,89.69999694824219,1196,1865.2000
274658203_SX89_AL_.jpg_V1_SX300.jpg",
"imdb" : {
"id" : "tt0067328",
"rating" : 8.1,
"votes" : 29830
},
"awards" : {
"wins" : 16,
"nominations" : 22,
"text" : "Won 2 Oscars. Another 16 wins & 22 nominations."
},
"type" : "movie"
}
..............................
{
"_id" : ObjectId("5692a14e24de1e0ce2dfcf56"),
"title" : "Crazy Heart",
"year" : 2009,
"rated" : "R",
"released" : ISODate("2010-02-05T05:00:00Z"),
"runtime" : 112,
"countries" : [
"USA"
],
"genres" : [
"Drama",
"Music",
"Romance"
],
"director" : "Scott Cooper",
"writers" : [
"Scott Cooper",
"Thomas Cobb"
],
"actors" : [
"Jeff Bridges",
"James Keane",
"Anna Felix",
"Paul Herman"
],
"plot" : "A faded country music musician is forced to reassess his dysfu
nctional life during a doomed romance that also inspires him.",
"poster" : "http://ia.media-imdb.com/images/M/MV5BMTU0NDc5NjgzNl5BMl5Ban
BnXkFtZTcwNzc0NDIzMw@@._V1_SX300.jpg",
"imdb" : {
"id" : "tt1263670",
"rating" : 7.3,
"votes" : 63771
},
"tomato" : {
"meter" : 91,
"image" : "certified",
"rating" : 7.4,
"reviews" : 199,
"fresh" : 181,
"consensus" : "Thanks to a captivating performance from Jeff Bri
dges, Crazy Heart transcends its overly familiar origins and finds new meaning i
n an old story.",
"userMeter" : 76,
"userRating" : 3.6,
"userReviews" : 124175
},
"metacritic" : 83,
"awards" : {
"wins" : 32,
"nominations" : 26,
"text" : "Won 2 Oscars. Another 32 wins & 26 nominations."
},
"type" : "movie"
}
>- 过滤读取 数组中指定的某位置的者某特定元素
比如我要查找actors字段的第三个元素为“Jeff Bridges”的document。
find({"actors.2":"Jeff Bridges"})> db.movieDetails.find({"actors.2":"Jeff Bridges"}).pretty()
{
"_id" : ObjectId("5692a15424de1e0ce2dfcf98"),
"title" : "Iron Man",
"year" : 2008,
"rated" : "PG-13",
"released" : ISODate("2008-05-02T04:00:00Z"),
"runtime" : 126,
"countries" : [
"USA"
],
"genres" : [
"Action",
"Adventure",
"Sci-Fi"
],
"director" : "Jon Favreau",
"writers" : [
"Mark Fergus",
"Hawk Ostby",
"Art Marcum",
"Matt Holloway",
"Stan Lee",
"Don Heck",
"Larry Lieber",
"Jack Kirby"
],
"actors" : [
"Robert Downey Jr.",
"Terrence Howard",
"Jeff Bridges",
"Gwyneth Paltrow"
],
"plot" : "After being held captive in an Afghan cave, an industrialist c
reates a unique weaponized suit of armor to fight evil.",
"poster" : "http://ia.media-imdb.com/images/M/MV5BMTczNTI2ODUwOF5BMl5Ban
BnXkFtZTcwMTU0NTIzMw@@._V1_SX300.jpg",
"imdb" : {
"id" : "tt0371746",
"rating" : 7.9,
"votes" : 641369
},
"tomato" : {
"meter" : 94,
"image" : "certified",
"rating" : 7.7,
"reviews" : 266,
"fresh" : 249,
"consensus" : "Director Jon Favreau and star Robert Downey Jr. m
ake this smart, high impact superhero movie one that even non-comics fans can en
joy.",
"userMeter" : 91,
"userRating" : 4.2,
"userReviews" : 1072887
},
"metacritic" : 79,
"awards" : {
"wins" : 19,
"nominations" : 58,
"text" : "Nominated for 2 Oscars. Another 19 wins & 58 nominatio
ns."
},
"type" : "movie"
}
>- 更复杂的匹配读取，后文中再讨论
CURSOR指针
前文说过，在shell中，db.mycoll.find()返回是一个指针对象。而且默认情况下，每次返回内容默认是这个指针对象遍历20次的内容集合。
.......
Type "it" for more通过使用it再次遍历20次，并返回20次的总结果集合。
通常，mongoDB是以batches（批量）方式返回查询集合。对于大多数查询，第一个批量返回101条document.比如:
第一个批量总共返回101条document，第二个批量返回剩余的21条document。
> db.funnynumbers.find().count()
122
> var iterator=db.funnynumbers.find();
> var eachDoc=function(){return iterator.hasNext()?iterator.next():null}
> iterator.objsLeftInBatch()
101
> eachDoc()
{ "_id" : ObjectId("50778ce69331a280cf4bcf7d"), "value" : 87 }
> iterator.objsLeftInBatch()
100
> eachDoc()
{ "_id" : ObjectId("50778ce69331a280cf4bcf7e"), "value" : 34 }
> iterator.objsLeftInBatch()
99
Projection
一种实现部分缩减返回数据的手段（通常针对单个查询）。通过减少返回document中的fields,来减少网络开销以及系统负载。
通常 Projection通过设置db.mycoll.find({},{})的第二个参数来实现。
比如：我要只返回（过滤：tomato字段中的meter字段为100的）document中的awards字段（可以看到“_id”并没有限制住，默认返回）。
> db.movieDetails.findOne({"tomato.meter":100},{"awards":1})
{
"_id" : ObjectId("569190d024de1e0ce2dfcd79"),
"awards" : {
"wins" : 2,
"nominations" : 2,
"text" : "Won 3 Oscars. Another 2 wins & 2 nominations."
}
}
>
>
> db.movieDetails.findOne({"tomato.meter":100},{type:0,tomato:0,writers:0,actors
:0,"_id":0,countries:0,genres:0})
{
"title" : "The Adventures of Robin Hood",
"year" : 1938,
"rated" : "PG",
"released" : ISODate("1938-05-14T04:00:00Z"),
"runtime" : 102,
"director" : "Michael Curtiz, William Keighley",
"plot" : "When Prince John and the Norman Lords begin oppressing the Sax
on masses in King Richard's absence, a Saxon lord fights back as the outlaw lead
er of a rebel guerrilla army.",
"poster" : "http://ia.media-imdb.com/images/M/MV5BMTUxMzE0MjI0MF5BMl5Ban
BnXkFtZTcwMTQ1OTM2MQ@@._V1_SX300.jpg",
"imdb" : {
"id" : "tt0029843",
"rating" : 8,
"votes" : 37543
},
"metacritic" : 97,
"awards" : {
"wins" : 2,
"nominations" : 2,
"text" : "Won 3 Oscars. Another 2 wins & 2 nominations."
}
}
>
>
> db.movieDetails.findOne({"tomato.meter":100},{"awards":1,_id:0})
{
"awards" : {
"wins" : 2,
"nominations" : 2,
"text" : "Won 3 Oscars. Another 2 wins & 2 nominations."
}
}所以:
find（）第二参数：｛“awards”:1,”_id”:0｝：
1表示只有这个字段需要返回（“_id”默认返回）；
0表示返回除这个字段之外的其他字段。