在 MongoDB 中查找已填充嵌套数组的文档并重新整理文档结果
mongodbdatabasebig data analytics更新于 2026/1/11 13:22:17
首先创建一个包含文档的集合 −
> db.demo187.insertOne(
... {
... "_id" : "101",
... "Details" : [
... { "Subject" : "MongoDB" },
... { "Subject" : "MySQL" }
... ]
... }
...);
{ "acknowledged" : true, "insertedId" : "101" }
> db.demo187.insertOne(
... {
... "_id" : "102",
... "Details" : [
... { }
... ]
... }
...);
{ "acknowledged" : true, "insertedId" : "102" }
> db.demo187.insertOne(
... {
... "_id" : "103",
... "Details" : [
... { "Subject" : "MongoDB" },
... { "Subject" : "MySQL" }
... ]
... }
...);
{ "acknowledged" : true, "insertedId" : "103" }
借助 find() 方法显示集合中的所有文档 −
> db.demo187.find();
这将产生以下输出 −
{ "_id" : "101", "Details" : [ { "Subject" : "MongoDB" }, { "Subject" : "MySQL" } ] }
{ "_id" : "102", "Details" : [ { } ] }
{ "_id" : "103", "Details" : [ { "Subject" : "MongoDB" }, { "Subject" : "MySQL" } ] }
以下是在 MongoDB 文档中查找填充嵌套数组的查询 −
> db.demo187.aggregate([
...
... {$unwind: '$Details'},
...
... {$project: {Subject: '$Details.Subject'}},
...
... {$match: {Subject: {$exists: true}}}
... ])
这将产生以下输出 −
{ "_id" : "101", "Subject" : "MongoDB" }
{ "_id" : "101", "Subject" : "MySQL" }
{ "_id" : "103", "Subject" : "MongoDB" }
{ "_id" : "103", "Subject" : "MySQL" }
