三 表达式操作符
6、字符串类型聚合操作符
1)$concat
作用:连接字符串,如果某个表达式字段不存在或字段值为null,则返回null
语法:{ $concat: [ <expression1>,<expression2>,… ] }
示例
{ "_id" : 1,"item" : "ABC1",quarter: "13Q1","description" : "product 1" }
{ "_id" : 2,"item" : "ABC2",quarter: "13Q4","description" : "product 2" }
{ "_id" : 3,"item" : "XYZ1",quarter: "14Q2","description" : null }
db.inventory.aggregate(
[
{ $project: { itemDescription: { $concat: [ "$item"," - ","$description" ] } } }
]
)
结果如下
{ "_id" : 1,"itemDescription" : "ABC1 - product 1" }
{ "_id" : 2,"itemDescription" : "ABC2 - product 2" }
{ "_id" : 3,"itemDescription" : null }
2)$toLower|$toUpper
作用:将一个字符串全部转为小写|大写,如果该字符串为null,则返回空字符串。
语法:{ $toLower: <expression> }|{ $toUpper: <expression> }
示例
{ "_id" : 1,"description" : "PRODUCT 1" }
{ "_id" : 2,"item" : "abc2","description" : "Product 2" }
{ "_id" : 3,"item" : "xyz1","description" : null }
db.inventory.aggregate(
[
{
$project:
{
upItem: { $toLower: "$item" },
upDescription: { $toLower: "$description" },
loItem: { $toUpper: "$item" },
loDescription: { $toUpper: "$description" }
}
}
]
)
结果如下
{ "_id" : 1,"upItem" : "ABC1","upDescription" : "PRODUCT 1","loItem" : "abc1","loDescription" : "product 1" }
{ "_id" : 2,"upItem" : "ABC2","upDescription" : "PRODUCT 2","loItem" : "abc2","loDescription" : "product 2" }
{ "_id" : 3,"upItem" : "XYZ1","upDescription" : "","loItem" : "xyz1","loDescription" : "" }
3)$split
作用:根据指定字符串分割字符串,返回分割后的字符串数组
语法:{ $split: [ <string expression>,<delimiter> ] }
示例
{ "_id" : 1,"city" : "Berkeley,CA","qty" : 648 }
{ "_id" : 2,"city" : "Bend,OR","qty" : 491 }
{ "_id" : 3,"city" : "Kensington,"qty" : 233 }
{ "_id" : 4,"city" : "Eugene,"qty" : 842 }
{ "_id" : 5,"city" : "Reno,NV","qty" : 655 }
{ "_id" : 6,"city" : "Portland,"qty" : 408 }
{ "_id" : 7,"city" : "Sacramento,"qty" : 574 }
汇总每个州的qty的总大小,并按其大小排序
db.deliveries.aggregate([
{ $project : { city_state : { $split: ["$city",","] },qty : 1 } },
{ $unwind : "$city_state" },
{ $match : { city_state : /[A-Z]{2}/ } },
{ $group : { _id: { "state" : "$city_state" },total_qty : { "$sum" : "$qty" } } },
{ $sort : { total_qty : -1 } }
]);
{ "_id" : { "state" : "OR" },"total_qty" : 1741 }
{ "_id" : { "state" : "CA" },"total_qty" : 1455 }
{ "_id" : { "state" : "NV" },"total_qty" : 655 }
4)$substr
5)$indexOfBytes
6)$indexOfCP
7)$strLenBytes
8)$strLenCP
9)$strcasecmp
10)$substrBytes
11)$substrCP
7、日期类型聚合操作符
1)年月日等
$dayOfYear:该时间在一年中是第几天,范围1至366
$dayOfMonth:该时间在一月中是第几天,范围1至31
$dayOfWeek:该时间在一周中是第几天,范围1(Sunday)至7(Saturday)
$year:该时间属于哪一年
$month:该时间属于哪一月
$week:该时间在一年中是第几周,范围从0至53
$hour:该时间的小时
$minute:该时间的分钟
$second:该时间的秒数
$millisecond:该时间的毫秒数
示例
{ "_id" : 1,"item" : "abc","price" : 10,"quantity" : 2,"date" : ISODate("2014-01-01T08:15:39.736Z") }
db.sales.aggregate(
[
{
$project:
{
year: { $year: "$date" },
month: { $month: "$date" },
day: { $dayOfMonth: "$date" },
hour: { $hour: "$date" },
minutes: { $minute: "$date" },
seconds: { $second: "$date" },
milliseconds: { $millisecond: "$date" },
dayOfYear: { $dayOfYear: "$date" },
dayOfWeek: { $dayOfWeek: "$date" },
week: { $week: "$date" }
}
}
]
)
结果如下
{
"_id" : 1,
"year" : 2014,
"month" : 1,
"day" : 1,
"hour" : 8,
"minutes" : 15,
"seconds" : 39,
"milliseconds" : 736,
"dayOfYear" : 1,
"dayOfWeek" : 4,
"week" : 0
}
2)$dateToString
作用:根据要求格式化时间对象
语法:{ $dateToString: { format: <formatString>,date: <dateExpression> } }
示例
{"_id" : 1,"date" : ISODate("2014-01-01T08:15:39.736Z")}
db.sales.aggregate(
[
{
$project: {
yearMonthDayUTC: { $dateToString: { format: "%Y-%m-%d",date: "$date" } },
time: { $dateToString: { format: "%H:%M:%S:%L",date: "$date" } }
}
}
]
)
结果如下
{ "_id" : 1,"yearMonthDayUTC" : "2014-01-01","time" : "08:15:39:736" }
3)$isoDayOfWeek:
4)$isoWeek:
5)$isoWeekYear:
8、条件类型聚合操作符
1)$cond
语法
{ $cond: { if: <boolean-expression>,then: <true-case>,else: <false-case-> } } 或
{ $cond: [ <boolean-expression>,<true-case>,<false-case> ] }
作用
$cond为mongoDB的三元运算符
示例
{ "_id" : 1,"item" : "abc1",qty: 300 }
{ "_id" : 2,qty: 200 }
{ "_id" : 3,qty: 250 }
查询如果qty大于250,则discount为30,否则为20
db.inventory.aggregate(
[
{
$project:
{
item: 1,
discount:
{
$cond: { if: { $gte: [ "$qty",250 ] },then: 30,else: 20 }
}
}
}
]
)
或
db.inventory.aggregate(
[
{
$project:
{
item: 1,
discount:
{
$cond: [ { $gte: [ "$qty",30,20 ]
}
}
}
]
)
结果如下
{ "_id" : 1,"discount" : 30 }
{ "_id" : 2,"discount" : 20 }
{ "_id" : 3,"discount" : 30 }
2)$ifNull
作用:非空判断操作,如果为空,则用默认的值替代,如果非空,则保持原值
语法:{ $ifNull: [ <expression>,<replacement-expression-if-null> ] }
示例
{ "_id" : 1,description: "product 1",description: null,qty: 250 }
db.inventory.aggregate(
[
{
$project: {
item: 1,
description: { $ifNull: [ "$description","Unspecified" ] }
}
}
]
)
结果如下
{ "_id" : 1,"description" : "Unspecified" }
{ "_id" : 3,"description" : "Unspecified" }
3)$switch
作用:
语法:
$switch: {
branches: [
{ case: <expression>,then: <expression> },
{ case: <expression>,
...
],
default: <expression>
}
示例
{ "_id" : 1,"name" : "Susan Wilkes","scores" : [ 87,86,78 ] }
{ "_id" : 2,"name" : "Bob Hanna","scores" : [ 71,64,81 ] }
{ "_id" : 3,"name" : "James Torrelio","scores" : [ 91,84,97 ] }
db.grades.aggregate( [
{
$project:
{
"name" : 1,
"summary" :
{
$switch:
{
branches: [
{
case: { $gte : [ { $avg : "$scores" },90 ] },
then: "Doing great!"
},
{
case: { $and : [ { $gte : [ { $avg : "$scores" },80 ] },
{ $lt : [ { $avg : "$scores" },90 ] } ] },
then: "Doing pretty well."
},
{
case: { $lt : [ { $avg : "$scores" },
then: "Needs improvement."
}
],
default: "No scores found."
}
}
}
}
] )
结果如下
{ "_id" : 1,"summary" : "Doing pretty well." }
{ "_id" : 2,"summary" : "Needs improvement." }
{ "_id" : 3,"summary" : "Doing great!" }
9、集合类型聚合操作符
1)$setEquals
2)$setIntersection
语法:
{ $setIntersection: [ <array1>,<array2>,… ] }
作用
获取两个或多个数组的交集
示例
{ "_id" : 4,"A" : [ "red","blue" ],"B" : [ "green","red" ] }
db.experiments.aggregate([{ $project: { A: 1,B: 1,commonToBoth: { $setIntersection: [ "$A","$B" ] },_id: 0 } }])
结果如下
{ "A" : [ "red","red" ],"commonToBoth" : [ "red" ] }
3)$setUnion
4)$setDifference
5)$setIsSubset
6)$anyElementTrue
7)$allElementsTrue
10、文本搜索类型聚合操作符
1)$meta
11、变量类型聚合操作符
1)$let
12、文字类型聚合操作符
1)$literal
13、数据类型聚合操作符
1)$type