mongodb的group簡析 數據如下 www.2cto.com { _id : 0, name : hexin0, value : 0, date : ISODate(2012-12-19T11:48:07.151Z), group : 0 } { _id : 1, name : hexin1, value : 1, date : ISODate(2012-12-19T11:48:07.151Z), group : 1 } { _id : 2, name :

數據如下 www.2cto.com

{ "_id" : 0, "name" : "hexin0", "value" : 0, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 0 }

{ "_id" : 1, "name" : "hexin1", "value" : 1, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 1 }

{ "_id" : 2, "name" : "hexin2", "value" : 2, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 2 }

{ "_id" : 3, "name" : "hexin3", "value" : 3, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 0 }

{ "_id" : 4, "name" : "hexin4", "value" : 4, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 1 }

{ "_id" : 5, "name" : "hexin5", "value" : 5, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 2 }

{ "_id" : 6, "name" : "hexin6", "value" : 6, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 0 }

{ "_id" : 7, "name" : "hexin7", "value" : 7, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 1 }

{ "_id" : 8, "name" : "hexin8", "value" : 8, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 2 }

{ "_id" : 9, "name" : "hexin9", "value" : 9, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 0 }

{ "_id" : 10, "name" : "hexin10", "value" : 10, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 1 }

{ "_id" : 11, "name" : "hexin11", "value" : 11, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 2 }

{ "_id" : 12, "name" : "hexin12", "value" : 12, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 0 }

{ "_id" : 13, "name" : "hexin13", "value" : 13, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 1 }

{ "_id" : 14, "name" : "hexin14", "value" : 14, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 2 }

{ "_id" : 15, "name" : "hexin15", "value" : 15, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 0 }

{ "_id" : 16, "name" : "hexin16", "value" : 16, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 1 }

{ "_id" : 17, "name" : "hexin17", "value" : 17, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 2 }

{ "_id" : 18, "name" : "hexin18", "value" : 18, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 0 }

{ "_id" : 19, "name" : "hexin19", "value" : 19, "date" : ISODate("2012-12-19T11:48:07.151Z"), "group" : 1 }

需要實現下面sql :

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select date as d_o_f , goup ,sum(value),count(*),avg(sum(value)/count(*))

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from xx

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where name like 'hexin%'

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group by goup, date

www.2cto.com

1.定義分組的key

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StringBuilder keyfun = new StringBuilder();

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keyfun.append("function(d) {");

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keyfun.append(" return { ");

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keyfun.append(" goup : d.group ,");

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keyfun.append(" d_o_f: d.date.getDay() ");

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keyfun.append(" } ;");

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keyfun.append(" }");

2. 遍歷每個組的處理方式

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StringBuffer reduce = new StringBuffer();

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reduce.append("function ( curr, result) {");

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reduce.append(" result.total += curr.value; ");

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reduce.append(" result.count++;");

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reduce.append("}");

3. 計算平均數

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StringBuffer finalize = new StringBuffer();

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finalize.append("function(result){");

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finalize.append(" var weekdays = [ '星期天', '星期一', '星期二',");

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finalize.append(" '星期三', '星期四', ");

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finalize.append(" '星期五', '星期六' ];");

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finalize.append(" result.d_o_f = weekdays[result.d_o_f]; ");

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finalize.append(" result.avg = Math.round(result.total / result.count); ");

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finalize.append("}");

4. 調用dao查詢

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Group group = Group.keyFunction(keyfun.toString()).initial("count", 0).initial("total", 0)

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.reduce(reduce.toString()).finalizeFunction(finalize.toString());

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//調用自己封裝的dao來實現 ， 并輸出結果

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List> list = dao.group("c", Query.where("name").startWith("hexin"), group);

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for (Map map : list) {

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System.out.println(map);

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}

封裝的查詢條件 ：

www.2cto.com

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{ "$regex" : { "$regex" : "^hexin" , "$options" : "m"}}

封裝的group命令

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{

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"group": {

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"$keyf": "function(d) { return { goup : d.group , d_o_f: d.date.getDay() } ; }",

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"$reduce": "function ( curr, result) {result.total += curr.value; result.count++;}",

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"initial": {

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"total": 0,

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"count": 0

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},

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"finalize": "function(result){

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var weekdays = [ '星期天', '星期一', '星期二','星期三', '星期四','星期五', '星期六' ];

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result.d_o_f = weekdays[result.d_o_f];

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result.avg = Math.round(result.total / result.count);

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}",

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"ns": "c",

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"cond": {

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"name": {

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"$regex": {

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"$regex": "^hexin",

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"$options": "m"

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}

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}

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}

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}

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}

/////查詢結果

{goup=0.0, d_o_f=星期三, total=63.0, count=7.0, avg=9.0}

{goup=1.0, d_o_f=星期三, total=70.0, count=7.0, avg=10.0}

{goup=2.0, d_o_f=星期三, total=57.0, count=6.0, avg=10.0}

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