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, "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:
{
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, CA", "qty" : 233 }
{ "_id" : 4, "city" : "Eugene, OR", "qty" : 842 }
{ "_id" : 5, "city" : "Reno, NV", "qty" : 655 }
{ "_id" : 6, "city" : "Portland, OR", "qty" : 408 }
{ "_id" : 7, "city" : "Sacramento, CA", "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
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,"item" : "abc","price" : 10,"quantity" : 2,"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)$isoWeekYear:
1)$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, "item" : "abc2", qty: 200 }
{ "_id" : 3, "item" : "xyz1", 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", 250 ] }, 30, 20 ]
}
}
}
]
)
结果如下
{ "_id" : 1, "item" : "abc1", "discount" : 30 }
{ "_id" : 2, "item" : "abc2", "discount" : 20 }
{ "_id" : 3, "item" : "xyz1", "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, "item" : "abc1", description: "product 1", qty: 300 }
{ "_id" : 2, "item" : "abc2", description: null, qty: 200 }
{ "_id" : 3, "item" : "xyz1", qty: 250 }
db.inventory.aggregate(
[
{
$project: {
item: 1,
description: { $ifNull: [ "$description", "Unspecified" ] }
}
}
]
)
结果如下
{ "_id" : 1, "item" : "abc1", "description" : "product 1" }
{ "_id" : 2, "item" : "abc2", "description" : "Unspecified" }
{ "_id" : 3, "item" : "xyz1", "description" : "Unspecified" }
3)$switch
作用:
语法:
$switch: {
branches: [
{ case: , then: },
{ case: , then: },
...
],
default:
}
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" }, 80 ] },
then: "Needs improvement."
}
],
default: "No scores found."
}
}
}
}
] )
结果如下
{ "_id" : 1, "name" : "Susan Wilkes", "summary" : "Doing pretty well." }
{ "_id" : 2, "name" : "Bob Hanna", "summary" : "Needs improvement." }
{ "_id" : 3, "name" : "James Torrelio", "summary" : "Doing great!" }
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", "$B" ] }, _id: 0 } }])
结果如下
{ "A" : [ "red", "blue" ], "B" : [ "green", "red" ], "commonToBoth" : [ "red" ] }
3)$setUnion
4)$setDifference
5)$setIsSubset
6)$anyElementTrue
7)$allElementsTrue
1)$meta
1)$let
1)$literal
1)$type