使用聚合框架可以對(duì)集合中的文檔進(jìn)行變換和組合。用多個(gè)構(gòu)件創(chuàng)建一個(gè)管道(pipeline),用于對(duì)一連串的文檔進(jìn)行處理。這些構(gòu)件包括:
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篩選(filtering)
投射(projecting)
分組(grouping)
排序(sorting)
限制(limiting)
跳過(skipping)
在MongoDB中實(shí)際的集合框架,需要將這些操作傳給aggregate函數(shù),例如:
(1)將文檔的name字段投射出來
> db.post.aggregate({$project:{"name":1}}) { "_id" : ObjectId("54a530c3ff0df3732bac1681"), "name" : "joe" } { "_id" : ObjectId("54a530c3ff0df3732bac1680"), "name" : "joe" } { "_id" : ObjectId("54a9700e1b5afd45354fd086") } { "_id" : ObjectId("54a9701c1b5afd45354fd087") } { "_id" : ObjectId("54a970281b5afd45354fd088") } { "_id" : ObjectId("54a970351b5afd45354fd089") } { "_id" : ObjectId("54a970781b5afd45354fd08a") } { "_id" : ObjectId("54a970831b5afd45354fd08b") } { "_id" : ObjectId("54a970901b5afd45354fd08c") } { "_id" : ObjectId("54a9709c1b5afd45354fd08d") } { "_id" : ObjectId("54aa8a90652d8bdfa0566d34") } { "_id" : ObjectId("54aa97b894dcf31069b590ca") } { "_id" : ObjectId("54aa97d794dcf31069b590cb") } { "_id" : ObjectId("54aa97f294dcf31069b590cc") } { "_id" : ObjectId("54aff7f43bd1048e7b585e39") } > db.post.aggregate({$project:{"name":1,"_id":0}}) { "name" : "joe" } { "name" : "joe" }
可以看的出了find的用法類似;
(2)以name字段的值對(duì)其分組并計(jì)算其個(gè)數(shù)
> db.post.aggregate({$group:{"_id":"$name","count":{$sum:1}}}) { "_id" : null, "count" : 13 } { "_id" : "joe", "count" : 2 } >
(3)對(duì)結(jié)果集進(jìn)行降序排列
> db.post.aggregate({$sort:{"id":-1}}) { "_id" : ObjectId("54aa97d794dcf31069b590cb"), "id" : 13, "fruit" : [ "apple", "kumquat", "orange", "fruit01" ] } { "_id" : ObjectId("54aa97b894dcf31069b590ca"), "id" : 12, "fruit" : [ "apple", "banana", "peach" ] } { "_id" : ObjectId("54aa8a90652d8bdfa0566d34"), "id" : 11, "test10" : 11 } { "_id" : ObjectId("54a9709c1b5afd45354fd08d"), "id" : 10, "test10" : 10 } { "_id" : ObjectId("54a970901b5afd45354fd08c"), "id" : 9, "test9" : 9 } { "_id" : ObjectId("54a970831b5afd45354fd08b"), "id" : 8, "test8" : 8 } { "_id" : ObjectId("54a970781b5afd45354fd08a"), "id" : 7, "test7" : 7 } { "_id" : ObjectId("54a970351b5afd45354fd089"), "id" : 6, "test6" : 6 } { "_id" : ObjectId("54a970281b5afd45354fd088"), "id" : 5, "test5" : 5 } { "_id" : ObjectId("54a9701c1b5afd45354fd087"), "id" : 4, "test4" : 4 } { "_id" : ObjectId("54a9700e1b5afd45354fd086"), "id" : 3, "test3" : 3 } { "_id" : ObjectId("54a530c3ff0df3732bac1681"), "id" : 2, "name" : "joe", "age" : 30, "sex" : 1, "school" : "marry" } { "_id" : ObjectId("54a530c3ff0df3732bac1680"), "id" : 1, "name" : "joe", "age" : 30, "comments" : [ "test2", "test9", "test5" ], "sex" : 1, "school" : "marry" } { "_id" : ObjectId("54aa97f294dcf31069b590cc"), "push" : { "fruit" : "fruit01" } } { "_id" : ObjectId("54aff7f43bd1048e7b585e39"), "username" : "sid", "loc" : { "ip" : "1.2.3.4", "city" : "springfield", "state" : "ny" } } >
(4)限制顯示排序后的前5個(gè)結(jié)果
> db.post.aggregate({$sort:{"id":-1}},{$limit:5}) { "_id" : ObjectId("54aa97d794dcf31069b590cb"), "id" : 13, "fruit" : [ "apple", "kumquat", "orange", "fruit01" ] } { "_id" : ObjectId("54aa97b894dcf31069b590ca"), "id" : 12, "fruit" : [ "apple", "banana", "peach" ] } { "_id" : ObjectId("54aa8a90652d8bdfa0566d34"), "id" : 11, "test10" : 11 } { "_id" : ObjectId("54a9709c1b5afd45354fd08d"), "id" : 10, "test10" : 10 } { "_id" : ObjectId("54a970901b5afd45354fd08c"), "id" : 9, "test9" : 9 } >
聚合框架類似關(guān)系行數(shù)據(jù)庫中的select,不會(huì)對(duì)集合進(jìn)行寫入操作,結(jié)果只會(huì)返回給客戶端。
本文名稱:【MongoDB學(xué)習(xí)筆記30】MongoDB的聚合框架
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