python操作mongodb之二聚合查询
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#聚合查询 from pymongo import MongoClient db = MongoClient(‘mongodb://10.0.0.9:27017/‘).aggregation_example #准备数据 result = db.things.insert_many([{"x": 1, "tags": ["dog", "cat"]}, {"x": 2, "tags": ["cat"]}, {"x": 2, "tags": ["mouse", "cat", "dog"]}, {"x": 3, "tags": []}]) result.inserted_ids ‘‘‘ { "_id" : ObjectId("576aaa973e5269020848cc7c"), "x" : 1, "tags" : [ "dog", "cat" ] } { "_id" : ObjectId("576aaa973e5269020848cc7d"), "x" : 2, "tags" : [ "cat" ] } { "_id" : ObjectId("576aaa973e5269020848cc7e"), "x" : 2, "tags" : [ "mouse", "cat", "dog" ] } { "_id" : ObjectId("576aaa973e5269020848cc7f"), "x" : 3, "tags" : [ ] } ‘‘‘ from bson.son import SON #$unwind 解开-后面的变量 pipeline = [ {"$unwind": "$tags"}, {"$group": {"_id": "$tags", "count": {"$sum": 1}}}, {"$sort": SON([("count", -1), ("_id", -1)])} ] list(db.things.aggregate(pipeline)) #使用聚合函数with command db.command(‘aggregate‘, ‘things‘, pipeline=pipeline, explain=True) """Map/Reduce""" from bson.code import Code mapper = Code(""" function () { this.tags.forEach(function(z) { emit(z, 1); }); } """) reducer = Code(""" function (key, values) { var total = 0; for (var i = 0; i < values.length; i++) { total += values[i]; } return total; } """) result = db.things.map_reduce(mapper, reducer, "myresults") for doc in result.find(): print doc
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