在 MongoDB 中检查数组是否重复?
mongodbdatabasebig data analytics更新于 2026/1/16 19:22:17
要检查数组是否重复，请使用 MongoDB 中的 aggregate() 方法。让我们创建一个包含文档的集合 −
> db.demo756.insertOne({"SubjectName":["MySQL","MongoDB","Java"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5eb01e0d5637cd592b2a4add")
}
> db.demo756.insertOne({"SubjectName":["MongoDB","MySQL","MongoDB","C","C+","MySQL"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5eb01e2b5637cd592b2a4ade")
}
借助 find() 方法显示集合中的所有文档 −
> db.demo756.find();
这将产生以下输出 −
{ "_id" : ObjectId("5eb01e0d5637cd592b2a4add"), "SubjectName" : [ "MySQL", "MongoDB", "Java" ] }
{ "_id" : ObjectId("5eb01e2b5637cd592b2a4ade"), "SubjectName" : [ "MongoDB", "MySQL", "MongoDB", "C", "C+", "MySQL" ] }
以下是检查数组中重复项的查询−
> db.demo756.aggregate([
... {"$project": {"SubjectName":1}},
... {"$unwind":"$SubjectName"},
... {"$group": {"_id":{"_id":"$_id", "Name":"$SubjectName"}, "count":{"$sum":1}}},
... {"$match": {"count":{"$gt":1}}},
... {"$group": {"_id": "$_id._id", "SubjectName":{"$addToSet":"$_id.Name"}}}
... ])
这将产生以下输出 −
{ "_id" : ObjectId("5eb01e2b5637cd592b2a4ade"), "SubjectName" : [ "MongoDB", "MySQL" ] }
