Mongo 聚合框架-Aggregate(二)
来源：互联网 发布：科比布莱恩特生涯数据 编辑：程序博客网 时间：2024/05/29 13:21
三 表达式操作符
1、布尔类型聚合操作符
1)＄and
作用：mongo中的与操作符，如果表达式全部为true则结果为true，否则为false
语法：{ ＄and: [ ＜expression1>, ＜expression2>, … ] }
示例：{ ＄and: [ 1, “green” ] } = true
2)＄or
作用：mongo中的或操作符，如果表达式全部为false则结果为false，否则为false
语法：{ ＄or: [ ＜expression1>, ＜expression2>, … ] }
示例：{ ＄or: [ [ false ], false ] } = true
3)＄not
作用：mongo中的非操作符，返回与表达式相反的boolean值
语法：{ ＄not: [ ] }
示例：{ ＄not: [ true ] } = false
2、比较类型聚合操作符
1)＄cmp (equal)
作用：比较两个值，如果第一个值小于第二个值，返回-1，如果大于第二个值，返回1，如果相等，返回0。＄cmp操作符会先按type比较，然后按value来比较。
语法：{ ＄cmp: [ ＜expression1>, ＜expression2> ] }
2)＄eq (=)
作用：比较两个值的大小，如果相等则返回true，否则返回false
语法：{ ＄eq: [ ＜expression1>, ＜expression2> ] }
3)＄gt (>)
作用：比较两个值的大小，如果第一个值大于第二个值则返回true，否则返回false
语法：{ ＄gt: [ ＜expression1>, ＜expression2> ] }
4)＄gte (>=)
作用：比较两个值的大小，如果第一个值大于等于第二个值则返回true，否则返回false
语法：{ ＄gte: [ ＜expression1>, ＜expression2> ] }
5)＄lt (<)
作用：比较两个值的大小，如果第一个值小于第二个值则返回true，否则返回false
语法：{ ＄lt: [ ＜expression1>, ＜expression2> ] }
6)＄lte (=＜)
作用：比较两个值的大小，如果第一个值小于等于第二个值则返回true，否则返回false
语法：{ ＄lte: [ ＜expression1>, ＜expression2> ] }
7)＄ne (!=)
作用：比较两个值的大小，如果不相等则返回true，否则返回false
语法：{ $ne: [ ＜expression1>, ＜expression2> ] }
8)示例
{ "_id" : 1, "item" : "abc1", description: "product 1", qty: 300 }{ "_id" : 2, "item" : "abc2", description: "product 2", qty: 200 }{ "_id" : 3, "item" : "xyz1", description: "product 3", qty: 250 }{ "_id" : 4, "item" : "VWZ1", description: "product 4", qty: 300 }{ "_id" : 5, "item" : "VWZ2", description: "product 5", qty: 180 }比较qty的值与250的大小db.inventory.aggregate( [ { $project: { item: 1, qty: 1, cmpTo250: { $cmp: [ "$qty", 250 ] }, qtyEq250: { $eq: [ "$qty", 250 ] }, qtyGt250: { $gt: [ "$qty", 250 ] }, qtyGte250: { $gte: [ "$qty", 250 ] }, qtyLt250: { $lt: [ "$qty", 250 ] }, qtyLte250: { $lte: [ "$qty", 250 ] }, qtyNe250: { $ne: [ "$qty", 250 ] }, _id: 0 } } ])结果如下{ "item" : "abc1", "qty" : 300, "cmpTo250" : 1, "qtyEq250" : false, "qtyGt250" : true, "qtyGte250" : true, "qtyLt250" : false, "qtyLte250" : false, "qtyNe250" : true }{ "item" : "abc2", "qty" : 200, "cmpTo250" :-1, "qtyEq250" : false, "qtyGt250" : false, "qtyGte250" : false, "qtyLt250" : true, "qtyLte250" : true, "qtyNe250" : true }{ "item" : "xyz1", "qty" : 250, "cmpTo250" : 0, "qtyEq250" : true, "qtyGt250" : false, "qtyGte250" : true, "qtyLt250" : false, "qtyLte250" : true, "qtyNe250" : false }{ "item" : "VWZ1", "qty" : 300, "cmpTo250" : 1, "qtyEq250" : false, "qtyGt250" : true, "qtyGte250" : true, "qtyLt250" : false, "qtyLte250" : false, "qtyNe250" : true }{ "item" : "VWZ2", "qty" : 180, "cmpTo250" :-1, "qtyEq250" : false, "qtyGt250" : false, "qtyGte250" : false, "qtyLt250" : true, "qtyLte250" : true, "qtyNe250" : true }3、分组类型聚合操作符
1)＄sum
作用
＄sum操作是对数进行求和操作，它会忽略非数字的值。
如果在一个即有数字值也有非数字值的字段上使用，＄sum只会返回数字值的和而将非数字的值忽略。
如果在一个所有文档中都不存在的字段上使用，返回0。
如果在一个所有值都不是数字类型的字段上使用，返回0
＄sum只在管道操作符＄group和＄project下有效
语法
{ ＄sum: ＜expression> }
＄project阶段还可能会有
{ ＄sum: [ ＜expression1>, ＜expression2> … ] }
2)＄avg
作用
＄avg操作是对数进行求平均数操作，它会忽略非数字的值。＄avg只在管道操作符＄group和＄project下有效
语法
{ ＄avg: ＜expression> }
$project阶段还可能会有
{ ＄avg: [ ＜expression1>, ＜expression2> … ] }
3)＄max：
作用
＄max是求最大值的一个操作，它会同时比较值的类型和大小，只在管道操作符＄group和＄project下有效。
语法
{ ＄max: ＜expression> }
$project阶段还可能会有
{ ＄max: [ ＜expression1>, ＜expression2> … ] }
4)＄min：只在管道操作符＄group和＄project下有效
作用
＄max是求最小值的一个操作，它会同时比较值的类型和大小，只在管道操作符＄group和＄project下有效。
语法
{ ＄min: ＜expression> }
＄project阶段还可能会有
{ ＄min: [ ＜expression1>, ＜expression2> … ] }
示例1($group stage)
{ "_id" : ObjectId("599e7c8c99657c350e726a63"), "item" : "abc", "price" : 10, "quantity" : 2, "date" : ISODate("2014-01-01T08:00:00Z") } { "_id" : ObjectId("599e7c8c99657c350e726a64"), "item" : "jkl", "price" : 20, "quantity" : 1, "date" : ISODate("2014-02-03T09:00:00Z") } { "_id" : ObjectId("599e7c8c99657c350e726a65"), "item" : "xyz", "price" : 5, "quantity" : 5, "date" : ISODate("2014-02-03T09:05:00Z") } { "_id" : ObjectId("599e7c8c99657c350e726a66"), "item" : "abc", "price" : 10, "quantity" : 10, "date" : ISODate("2014-02-15T08:00:00Z") } { "_id" : ObjectId("599e7c8e99657c350e726a67"), "item" : "xyz", "price" : 5, "quantity" : 10, "date" : ISODate("2014-02-15T09:05:00Z") } 根据item分组，求分组的数量、总的金额、平均数量、最大的总金额、最小的数量值 db.sales.aggregate( [ { $group: { _id: "$item", count: { $sum: 1 }, totalAmount: { $sum: { $multiply: [ "$price", "$quantity" ] } }, avgQuantity: { $avg: "$quantity" }, maxTotalAmount: { $max: { $multiply: [ "$price", "$quantity" ] } }, minQuantity: { $min: "$quantity" } } } ] ) 结果如下 { "_id" : "xyz", "count" : 2, "totalAmount" : 75, "avgQuantity" : 7.5, "maxTotalAmount" : 50, "minQuantity" : 5 } { "_id" : "jkl", "count" : 1, "totalAmount" : 20, "avgQuantity" : 1, "maxTotalAmount" : 20, "minQuantity" : 1 } { "_id" : "abc", "count" : 2, "totalAmount" : 120, "avgQuantity" : 6, "maxTotalAmount" : 100, "minQuantity" : 2 }示例2(＄project stage)
{ "_id" : 1, "quizzes" : [ 10, 6, 7 ], "final" : 80, "midterm" : 75 } { "_id" : 2, "quizzes" : [ 9, 10 ], "final" : 95, "midterm" : 80 } { "_id" : 3, "quizzes" : [ 4, 5, 5 ], "final" : 78, "midterm" : 70 } 求quizzes数组的和、平均值、最大值、最小值，求final和midterm的和、平均值、最大值、最小值。 db.students.aggregate([ { $project: { "_id":0, quizTotal: { $sum: "$quizzes"}, examTotal: { $sum: [ "$final", "$midterm" ] }, quizAvg: { $avg: "$quizzes"}, examAvg: { $avg: [ "$final", "$midterm" ] }, quizMax: { $max: "$quizzes"}, examMax: { $max: [ "$final", "$midterm" ] }, quizMin: { $min: "$quizzes"}, examMin: { $min: [ "$final", "$midterm" ] } } } ]) 结果如下 { "quizTotal" : 23, "examTotal" : 155, "quizAvg" : 7.666666666666667, "examAvg" : 77.5, "quizMax" : 10, "examMax" : 80, "quizMin" : 6, "examMin" : 75 } { "quizTotal" : 19, "examTotal" : 175, "quizAvg" : 9.5, "examAvg" : 87.5, "quizMax" : 10, "examMax" : 95, "quizMin" : 9, "examMin" : 80 } { "quizTotal" : 14, "examTotal" : 148, "quizAvg" : 4.666666666666667, "examAvg" : 74, "quizMax" : 5, "examMax" : 78, "quizMin" : 4, "examMin" : 70 }5)＄first|＄last
作用：获取分组中第一个|最后一个文档产生的值，只在管道操作符＄group下有效。当＄group阶段使用＄first|＄last操作符的时候，＄group必须在＄sort管道之后从而得到有序的文档。
语法：{ ＄first: ＜expression> }|{ ＄last: ＜expression> }
示例
{ "item" : "abc", "price" : 10, "quantity" : 2, "date" : ISODate("2014-01-01T08:00:00Z") } { "item" : "jkl", "price" : 20, "quantity" : 1, "date" : ISODate("2014-02-03T09:00:00Z") } { "item" : "xyz", "price" : 5, "quantity" : 5, "date" : ISODate("2014-02-03T09:05:00Z") } { "item" : "abc", "price" : 10, "quantity" : 10, "date" : ISODate("2014-02-15T08:00:00Z") } { "item" : "xyz", "price" : 5, "quantity" : 10, "date" : ISODate("2014-02-15T09:05:00Z") } { "item" : "xyz", "price" : 5, "quantity" : 5, "date" : ISODate("2014-02-15T12:05:10Z") } { "item" : "xyz", "price" : 5, "quantity" : 10, "date" : ISODate("2014-02-15T14:12:12Z") } 根据item和date字段进行排序，然后根据item进行分组，获取分组中的第一条和最后一条文档记录的date值 db.sales.aggregate( [ { $sort: { item: 1, date: 1 } }, { $group: { _id: "$item", firstSalesDate: { $first: "$date" }, lastSalesDate: { $last: "$date" } } } ] ) 结果如下 { "_id" : "xyz", "firstSalesDate" : ISODate("2014-02-03T09:05:00Z"), "lastSalesDate" : ISODate("2014-02-15T14:12:12Z") } { "_id" : "jkl", "firstSalesDate" : ISODate("2014-02-03T09:00:00Z"), "lastSalesDate" : ISODate("2014-02-03T09:00:00Z") } { "_id" : "abc", "firstSalesDate" : ISODate("2014-01-01T08:00:00Z"), "lastSalesDate" : ISODate("2014-02-15T08:00:00Z") }6)＄push：
作用：＄push用来将表达式中的值按分组加到对应的数组中，只在管道操作符＄group下有效
语法：{ ＄push: ＜expression> }
7)＄addToSet：
作用：＄addToSet用来将表达式中的值按分组加到对应的数组中,数组中的值不可重复，只在管道操作符＄group下有效
语法：{ ＄addToSet: ＜expression> }
示例3
{ "item" : "abc", "price" : 10, "quantity" : 2, "date" : ISODate("2014-01-01T08:00:00Z") } { "item" : "jkl", "price" : 20, "quantity" : 1, "date" : ISODate("2014-02-03T09:00:00Z") } { "item" : "xyz", "price" : 5, "quantity" : 5, "date" : ISODate("2014-02-03T09:05:00Z") } { "item" : "abc", "price" : 10, "quantity" : 10, "date" : ISODate("2014-02-15T08:00:00Z") } { "item" : "xyz", "price" : 5, "quantity" : 10, "date" : ISODate("2014-02-15T09:05:00Z") } { "item" : "xyz", "price" : 5, "quantity" : 5, "date" : ISODate("2014-02-15T12:05:10Z") } { "item" : "xyz", "price" : 5, "quantity" : 10, "date" : ISODate("2014-02-15T14:12:12Z") } 根据年和天分组，获取改天所有的item集合以及所有的item名称集合 db.sales.aggregate( [ { $group: { _id: { day: { $dayOfYear: "$date"}, year: { $year: "$date" } }, itemsSold: { $push: { item: "$item", quantity: "$quantity" } }, soldItems: { $addToSet: "$item" } } } ] ) 结果如下 { "_id" : { "day" : 46, "year" : 2014 }, "itemsSold" : [ { "item" : "abc", "quantity" : 10 }, { "item" : "xyz", "quantity" : 10 }, { "item" : "xyz", "quantity" : 5 }, { "item" : "xyz", "quantity" : 10 } ], "soldItems" : [ "xyz", "abc" ] } { "_id" : { "day" : 34, "year" : 2014 }, "itemsSold" : [ { "item" : "jkl", "quantity" : 1 }, { "item" : "xyz", "quantity" : 5 } ], "soldItems" : [ "xyz", "jkl" ] } { "_id" : { "day" : 1, "year" : 2014 }, "itemsSold" : [ { "item" : "abc", "quantity" : 2 } ], "soldItems" : [ "abc" ] }8)＄stdDevPop：
9)＄stdDevSamp：
4、算术类型聚合操作符
1)＄add
作用：将一组数进行相加操作，也可以对日期格式的字段增加毫秒数而改变时间
语法：{ ＄add: [ ＜expression1>, ＜expression2>, … ] }
示例
{ "_id" : 1, "item" : "abc", "price" : 10, "fee" : 2 }{ "_id" : 2, "item" : "jkl", "price" : 20, "fee" : 1 }{ "_id" : 3, "item" : "xyz", "price" : 5, "fee" : 0 }db.sales.aggregate( [ { $project: { item: 1, total: { $add: [ "$price", "$fee" ] } } } ])结果如下{ "_id" : 1, "item" : "abc", "total" : 12 }{ "_id" : 2, "item" : "jkl", "total" : 21 }{ "_id" : 3, "item" : "xyz", "total" : 5 }2)＄subtract
作用：将两个数进行相减
语法：{ ＄subtract: [ ＜expression1>, ＜expression2> ] }
示例
{ "_id" : 1, "item" : "abc", "price" : 10, "fee" : 2, "discount" : 5 }{ "_id" : 2, "item" : "jkl", "price" : 20, "fee" : 1, "discount" : 2 }db.sales.aggregate( [ { $project: { item: 1, total: { $subtract: [ { $add: [ "$price", "$fee" ] }, "$discount" ] } } } ] )结果如下{ "_id" : 1, "item" : "abc", "total" : 7 }{ "_id" : 2, "item" : "jkl", "total" : 19 }3)＄multiply
作用：对一组数进行相乘操作
语法：{ ＄multiply: [ ＜expression1>, ＜expression2>, … ] }
示例
{ "_id" : 1, "item" : "abc", "price" : 10, "quantity": 2 }{ "_id" : 2, "item" : "jkl", "price" : 20, "quantity": 1 }{ "_id" : 3, "item" : "xyz", "price" : 5, "quantity": 10 }db.sales.aggregate( [ { $project: { date: 1, item: 1, total: { $multiply: [ "$price", "$quantity" ] } } } ])结果如下{ "_id" : 1, "item" : "abc", "total" : 20 }{ "_id" : 2, "item" : "jkl", "total" : 20 }{ "_id" : 3, "item" : "xyz", "total" : 50 }4)$divide
作用：将两个数进行相除
语法：{ ＄divide: [ ＜expression1>, ＜expression2> ] }
示例：
{ "_id" : 1, "name" : "A", "hours" : 80, "resources" : 7 },{ "_id" : 2, "name" : "B", "hours" : 40, "resources" : 4 }db.planning.aggregate( [ { $project: { name: 1, workdays: { $divide: [ "$hours", 8 ] } } } ])结果如下{ "_id" : 1, "name" : "A", "workdays" : 10 }{ "_id" : 2, "name" : "B", "workdays" : 5 }5)＄mod
作用：对两个数进行求余操作
语法：{ ＄mod: [ ＜expression1>, ＜expression2> ] }
示例
{ "_id" : 1, "project" : "A", "hours" : 80, "tasks" : 7 }{ "_id" : 2, "project" : "B", "hours" : 40, "tasks" : 4 }db.planning.aggregate( [ { $project: { remainder: { $mod: [ "$hours", "$tasks" ] } } } ])结果如下{ "_id" : 1, "remainder" : 3 }{ "_id" : 2, "remainder" : 0 }6)＄abs
作用：对数值做绝对值操作
语法：{ ＄abs: ＜number> }
示例
{ _id: 1, start: 5, end: 8 }{ _id: 2, start: 4, end: 4 }{ _id: 3, start: 9, end: 7 }{ _id: 4, start: 6, end: 7 }db.ratings.aggregate([ { $project: { delta: { $abs: { $subtract: [ "$start", "$end" ] } } } }])结果如下{ "_id" : 1, "delta" : 3 }{ "_id" : 2, "delta" : 0 }{ "_id" : 3, "delta" : 2 }{ "_id" : 4, "delta" : 1 }7)＄ceil|＄floor
作用：对小数进行取整运算
语法：{ ＄ceil: ＜number> }|{ ＄floor: ＜number> }
示例
{ _id: 1, value: 9.25 }{ _id: 2, value: 8.73 }{ _id: 3, value: 4.32 }{ _id: 4, value: -5.34 }db.samples.aggregate([ { $project: { value: 1, ceilingValue: { $ceil: "$value" }, floorValue: { $floor: "$value" } } }])结果如下{ "_id" : 1, "value" : 9.25, "ceilingValue" : 10, "floorValue" : 9 }{ "_id" : 2, "value" : 8.73, "ceilingValue" : 9, "floorValue" : 8 }{ "_id" : 3, "value" : 4.32, "ceilingValue" : 5, "floorValue" : 4 }{ "_id" : 4, "value" : -5.34, "ceilingValue" : -5, "floorValue" : -6 }8)＄exp
9)＄pow
10)＄sqrt
11)＄ln
12)＄log
13)＄log10
14)＄trunc
5、数组类型聚合操作符
1)＄in
作用：查询某个特定的值是否存在指定的数组中
语法：{ ＄in: [ ＜expression>, ＜array expression> ] }
示例
{ "_id" : 1, "location" : "24th Street","in_stock" : [ "apples", "oranges", "bananas" ] }{ "_id" : 2, "location" : "36th Street","in_stock" : [ "bananas", "pears", "grapes" ] }{ "_id" : 3, "location" : "82nd Street","in_stock" : [ "cantaloupes", "watermelons", "apples" ] }db.fruit.aggregate([ { $project: { "store location" : "$location", "has bananas" : { $in: [ "bananas", "$in_stock" ] } } }])结果如下{ "_id" : 1, "store location" : "24th Street", "has bananas" : true }{ "_id" : 2, "store location" : "36th Street", "has bananas" : true }{ "_id" : 3, "store location" : "82nd Street", "has bananas" : false }2)＄size
作用：用来获取数组的大小
语法：{ ＄size: ＜expression> }
示例
{ "_id" : 1, "item" : "ABC1", "description" : "product 1", colors: [ "blue", "black", "red" ] }{ "_id" : 2, "item" : "ABC2", "description" : "product 2", colors: [ "purple" ] }{ "_id" : 3, "item" : "XYZ1", "description" : "product 3", colors: [ ] }db.inventory.aggregate( [ { $project: { item: 1, numberOfColors: { $size: "$colors" } } } ])结果如下{ "_id" : 1, "item" : "ABC1", "numberOfColors" : 3 }{ "_id" : 2, "item" : "ABC2", "numberOfColors" : 1 }{ "_id" : 3, "item" : "XYZ1", "numberOfColors" : 0 }3)＄slice
作用：返回一个数组的子集
语法：{ ＄slice: [ ＜array>, ＜position>, ＜n> ] }
position：如果如正数，则返回从数组开始，到数组position下标截止的子数组；如果是负数，则返回数组下标为position绝对值开始到数组结尾的子数组。数组下标1开始。
n：正数，限制返回子数组的大小
示例
{ "_id" : 1, "name" : "dave123", favorites: [ "chocolate", "cake", "butter", "apples" ] }{ "_id" : 2, "name" : "li", favorites: [ "apples", "pudding", "pie" ] }{ "_id" : 3, "name" : "ahn", favorites: [ "pears", "pecans", "chocolate", "cherries" ] }{ "_id" : 4, "name" : "ty", favorites: [ "ice cream" ] }db.users.aggregate([ { $project: { name: 1, threeFavorites: { $slice: [ "$favorites", 3 ] } } }])结果如下{ "_id" : 1, "name" : "dave123", "threeFavorites" : [ "chocolate", "cake", "butter" ] }{ "_id" : 2, "name" : "li", "threeFavorites" : [ "apples", "pudding", "pie" ] }{ "_id" : 3, "name" : "ahn", "threeFavorites" : [ "pears", "pecans", "chocolate" ] }{ "_id" : 4, "name" : "ty", "threeFavorites" : [ "ice cream" ] }4)＄isArray
作用：判断一个操作数是否是数组类型
语法：{ ＄isArray: [ ＜expression> ] }
示例
{ "_id" : 1, instock: [ "chocolate" ], ordered: [ "butter", "apples" ] }{ "_id" : 2, instock: [ "apples", "pudding", "pie" ] }{ "_id" : 3, instock: [ "pears", "pecans"], ordered: [ "cherries" ] }{ "_id" : 4, instock: [ "ice cream" ], ordered: [ ] }db.warehouses.aggregate([ { $project: { items: { $cond: { if: { $and: [ { $isArray: "$instock" }, { $isArray: "$ordered" } ] }, then: { $concatArrays: [ "$instock", "$ordered" ] }, else: "One or more fields is not an array." } } } }])结果如下{ "_id" : 1, "items" : [ "chocolate", "butter", "apples" ] }5)＄reverseArray
作用：将数组中的元素倒置
语法：{ ＄reverseArray: ＜array expression> }
示例
{ "_id" : 1, "name" : "dave123", "favorites" : [ "chocolate", "cake", "butter", "apples" ] }{ "_id" : 2, "name" : "li", "favorites" : [ "apples", "pudding", "pie" ] }{ "_id" : 3, "name" : "ahn", "favorites" : [ ] }{ "_id" : 4, "name" : "ty" }db.users.aggregate([ { $project: { name: 1, reverseFavorites: { $reverseArray: "$favorites" } } }])结果如下{ "_id" : 1, "name" : "dave123", "reverseFavorites" : [ "apples", "butter", "cake", "chocolate" ] }{ "_id" : 2, "name" : "li", "reverseFavorites" : [ "pie", "pudding", "apples" ] }{ "_id" : 3, "name" : "ahn", "reverseFavorites" : [ ] }{ "_id" : 4, "name" : "ty", "reverseFavorites" : null }6)＄arrayElemAt
作用：根据下标返回数组中指定元素
语法：{ ＄arrayElemAt: [ ＜array>, ＜idx> ] }
示例
{ "_id" : 1, "name" : "dave123", favorites: [ "chocolate", "cake", "butter", "apples" ] }{ "_id" : 2, "name" : "li", favorites: [ "apples", "pudding", "pie" ] }{ "_id" : 3, "name" : "ahn", favorites: [ "pears", "pecans", "chocolate", "cherries" ] }{ "_id" : 4, "name" : "ty", favorites: [ "ice cream" ] }db.users.aggregate([ { $project: { name: 1, first: { $arrayElemAt: [ "$favorites", 0 ] }, last: { $arrayElemAt: [ "$favorites", -1 ] } } }])结果如下{ "_id" : 1, "name" : "dave123", "first" : "chocolate", "last" : "apples" }{ "_id" : 2, "name" : "li", "first" : "apples", "last" : "pie" }{ "_id" : 3, "name" : "ahn", "first" : "pears", "last" : "cherries" }{ "_id" : 4, "name" : "ty", "first" : "ice cream", "last" : "ice cream" }7)＄arrayToObject
作用：将一组数组或者文档转为单个文档，数组必须大小为2，文档必须包含”k”和”v”字段
[ [ “item”, “abc123”], [ “qty”, 25 ] ]或[ { “k”: “item”, “v”: “abc123”}, { “k”: “qty”, “v”: 25 } ]
语法：{ ＄arrayToObject: ＜expression> }
示例
{ "_id" : 1, "item" : "ABC1", dimensions: [ { "k": "l", "v": 25} , { "k": "w", "v": 10 }, { "k": "uom", "v": "cm" } ] }{ "_id" : 2, "item" : "ABC2", dimensions: [ [ "l", 50], [ "w", 25 ], [ "uom", "cm" ] ] }db.inventory.aggregate( [ { $project: { item: 1, dimensions: { $arrayToObject: "$dimensions" } } } ])结果如下{ "_id" : 1, "item" : "ABC1", "dimensions" : { "l" : 25, "w" : 10, "uom" : "cm" } }{ "_id" : 2, "item" : "ABC2", "dimensions" : { "l" : 50, "w" : 25, "uom" : "cm" } }8)＄concatArrays
作用：合并数组,如果表达式中有非数组类型的值，则返回null
语法：{ ＄concatArrays: [ ＜array1>, ＜array2>, … ] }
示例
{ "_id" : 1, instock: [ "chocolate" ], ordered: [ "butter", "apples" ] }{ "_id" : 2, instock: [ "apples", "pudding", "pie" ] }{ "_id" : 3, instock: [ "pears", "pecans"], ordered: [ "cherries" ] }{ "_id" : 4, instock: [ "ice cream" ], ordered: [ ] }db.warehouses.aggregate([ { $project: { items: { $concatArrays: [ "$instock", "$ordered" ] } } }])结果如下{ "_id" : 1, "items" : [ "chocolate", "butter", "apples" ] }{ "_id" : 2, "items" : null }{ "_id" : 3, "items" : [ "pears", "pecans", "cherries" ] }{ "_id" : 4, "items" : [ "ice cream" ] }9)＄range
10)＄filter
11)＄indexOfArray
12)＄map
13)＄objectToArray
14)＄reduce
15)＄zip
- Mongo 聚合框架-Aggregate(二)
- Mongo 聚合框架-Aggregate(一)
- Mongo 聚合框架-Aggregate(三)
- Mongo 聚合框架优化-Aggregate(四)
- mongo aggregate聚合查询
- mongo aggregate
- mongo-aggregate
- 聚合 aggregate
- mongo聚合
- Mongo聚合
- LINQ Aggregate聚合学习
- mongodb aggregate 聚合操作
- MongoDB aggregate聚合
- MongoDB aggregate 聚合管道
- mongodb 聚合aggregate 乘法
- MongoDB中的聚合 aggregate
- MongoDB aggregate() 聚合
- 聚合函数 Aggregate Function
- 数组方法实现（一）————数组方法join()
- JPA之使用JPQL语句操作数据库
- 原 Spring + SpringMVC + Mybatis 整合，实现 CRUD (增删改查)
- 《机器学习实战》总结：ID3决策树
- uva10384 The Wall Pusher 推门游戏
- Mongo 聚合框架-Aggregate(二)
- XML的四种生成方式
- php表示一年，一个星期等时间，很好用，方便
- servlet -1
- 链表习题
- ubuntu 卸载 /安装google-chrome
- Oracle PL/SQL常用命令
- svg绘制简单图形
- NYOJ2-括号配对问题
