问题描述
我正在使用Map Reduce.问题是，如果没有.输入的文档> 100，那么我没有得到预期的编号.结果，但如果没有.输入文档的数量是< == 100，那么我得到的结果是预期的.
I am using Map Reduce. The problem is that if the no. input of documents is > 100, then I am not getting the expected no. of results but if the no. of input documents is <= 100, then I am getting the results as expected.
我得到的示例输出:
{
"_id" : "5504",
"value" : [
ObjectId("51c921bae4b0f0f776b339d2"),
ObjectId("51b06b5be4b021e44bc69755")
]
}
问题::如果有< = 100个用户文档(id:5504)，那么我得到的则是很多.输出数组中的ID的数量，但如果没有.文档> 100，那么我在输出数组中得到的ID很少.当没有时我得到了上面的输出.此用户的文档数是101，但是当它是100时，我得到了100个ID.为什么会有这种奇怪的行为?对此有什么解决方案?
Problem: If there are <= 100 documents for user (id:5504), then I am getting that many no. of ids in the output array but if the no. of documents >100, then I am getting very few ids in the output array. I got the above output when the no. of documents for this user was 101, but when it was 100, I got 100 ids. Why this strange behaviour and what's the solution for this?
地图功能:
db.system.js.save({
_id: "map1",
value: function () {
var value = {
"data": [{
"_id": this._id,
"creation_time": this.creation_time
}]
};
emit(this.user_id, value);
}
});
减少功能:
db.system.js.save({
_id: "reduce1",
value: function (key, values) {
var reducedValue = [];
for (var i = 0; i < values.length; i++) {
reducedValue.push({
"_id": values[i].data[0]._id,
"creation_time": values[i].data[0].creation_time
});
}
return {
data: reducedValue
};
}
});
最终确定功能:
db.system.js.save({
_id: "finalize1",
value: function (key, reducedValue) {
var a = reducedValue.data.sort(compare1);
var ids = [];
for (var i = 0; i < a.length; i++) {
ids.push(a[i]._id);
}
return ids;
}
});
比较功能:
db.system.js.save({
_id: "compare1",
value: function (a, b) {
if (a.creation_time < b.creation_time) return 1;
if (a.creation_time > b.creation_time) return -1;
return 0;
}
});
MapReduce()调用
db.notifications.mapReduce(map1, reduce1, {out: "notifications_result", query: {delivered:true, user_id:"5504"}, finalize: finalize1});
推荐答案
由于MongoDB可以多次调用reduce函数，因此必须确保功能幂等.只需对您的reduce函数进行一些修改即可解决问题:
Since MongoDB could call reduce function many times, you must ensure Function Idempotence. A little modification on your reduce function solves the problem:
db.system.js.save({
_id: "reduce1",
value: function (key, values) {
var reducedValue = [];
for (var i = 0; i < values.length; i++) {
for(var j = 0; j < values[i].data.length; j++) {
reducedValue.push({
"_id": values[i].data[j]._id,
"creation_time": values[i].data[j].creation_time
});
}
}
return {
data: reducedValue
};
}
});
请注意，现在也遍历了values[i].data数组，因为其他reduce1的返回调用了位于values数组中.
Note that now the values[i].dataarray is traversed too, because the return of other reduce1 calls are in the values array.
这篇关于Mongodb-Map-Reduce-不返回完整数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！