mongodb 如何查找具有相同字段的mongo文档
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How to find mongo documents with a same field
提问by Nikita Platonenko
I have a mongo collection, and I need to find documents in this collection, in wich fields name and adrress are equal.
我有一个 mongo 集合，我需要在这个集合中找到文档，其中名称和地址是相等的。
I have searched a lot, I could only find MongoDb query condition on comparing 2 fieldsand MongoDB: Unique and sparse compound indexes with sparse values, but in these questions they are looking for documents in which field a = field b, but I need to find document1.a == document2.a
我搜索了很多，我只能在比较 2 个字段和MongoDB 时找到MongoDb 查询条件：具有稀疏值的唯一和稀疏复合索引，但在这些问题中，他们正在寻找字段 a = 字段 b 中的文档，但我需要找到 document1.a == document2.a
回答by Stennie
You can find duplicates using the Aggregation Frameworkand $group.
Example data set up:
示例数据设置：
// Batch insert some test data
db.mycollection.insert([
{a:1, b:2, c:3},
{a:1, b:2, c:4},
{a:0, b:2, c:3},
{a:3, b:2, c:4}
])
Aggregation query:
聚合查询：
db.mycollection.aggregate(
{ $group: {
// Group by fields to match on (a,b)
_id: { a: "$a", b: "$b" },
// Count number of matching docs for the group
count: { $sum: 1 },
// Save the _id for matching docs
docs: { $push: "$_id" }
}},
// Limit results to duplicates (more than 1 match)
{ $match: {
count: { $gt : 1 }
}}
)
Example output:
示例输出：
{
"result" : [
{
"_id" : {
"a" : 1,
"b" : 2
},
"count" : 2,
"docs" : [
ObjectId("5162b2e7d650a687b2154232"),
ObjectId("5162b2e7d650a687b2154233")
]
}
],
"ok" : 1
}
