如何获取具有非唯一数组元素的文档？

我有以下的MongoDB文档：

{ _id: ObjectId('09de14821345dda65c471c99'), items: [ _id: ObjectId('34de64871345dfa655471c99'), _id: ObjectId('34de64871345dfa655471c91'), _id: ObjectId('34de64871345dfa655471c99'), ] }, { _id: ObjectId('09de14821345dda65c471c98'), items: [ _id: ObjectId('24de64871345dfa61271c10'), _id: ObjectId('24de64871345dfa61271c11'), _id: ObjectId('24de64871345dfa61271c11'), ] }, { _id: ObjectId('09de14821345dda65c471c07'), items: [ _id: ObjectId('24de64871345dfa61271c05'), _id: ObjectId('24de64871345dfa61271c06'), _id: ObjectId('24de64871345dfa61271c07'), ] } 

我需要find重复项目数组元素的所有文件。 所以从上面的文件我想得到以下结果：

 db.collection.documents.find({/** need query*/}).toArray(function (err, documents) { console.dir(documents); // documents with id's 09de14821345dda65c471c99 and 09de14821345dda65c471c98 }); 

我怎么能这样做？

Answer 1

为了对结果进行分组和匹配，您将需要使用聚合框架或Map / Reduce而不是简单的find()查询。

示例数据

您的示例文档包含一些错误：一些ObjectID太短，数组元素应该是embedded式文档（ {_id: ObjectId(...)} ）或简单的值。

对于我用过的testing数据：

 db.mydocs.insert([ { _id: ObjectId('09de14821345dda65c471c99'), items: [ ObjectId('34de64871345dfa655471c99'), ObjectId('34de64871345dfa655471c91'), ObjectId('34de64871345dfa655471c99') ] }, { _id: ObjectId('09de14821345dda65c471c98'), items: [ ObjectId('24de64871345ddfa61271c10'), ObjectId('24de64871345ddfa61271c11'), ObjectId('24de64871345ddfa61271c11') ] }, { _id: ObjectId('09de14821345dda65c471c07'), items: [ ObjectId('24de64871345ddfa61271c05'), ObjectId('24de64871345ddfa61271c06'), ObjectId('24de64871345ddfa61271c07') ] }]) 

聚合查询

这是一个使用mongo shell的聚合查询：

 db.mydocs.aggregate( // Unpack items array into stream of documents { $unwind: "$items" }, // Group by original document _id and item { $group: { _id: { _id: "$_id", item: "$items" }, count: { $sum: 1 } }}, // Limit to duplicated array items (1 or more count per document _id) { $match: { count: { $gt: 1 } }}, // (Optional) clean up the result formatting { $project: { _id: "$_id._id", item: "$_id.item", count: "$count" }} ) 

示例结果

 { "_id" : ObjectId("09de14821345dda65c471c98"), "count" : 2, "item" : ObjectId("24de64871345ddfa61271c11") } { "_id" : ObjectId("09de14821345dda65c471c99"), "count" : 2, "item" : ObjectId("34de64871345dfa655471c99") }