如何过滤对象中的某些字段并在MongoDB中获取特定的主题名称值？
要进行过滤和获取，请使用投影以及MongoDB$filter和$match。让我们创建一个包含文档的集合-
> db.demo507.insertOne(
... {
...
... "Information":
... [
... {"Name":"John","SubjectName":"MySQL"},
... {"Name":"Bob","SubjectName":"MongoDB"},
... {"Name":"Chris","SubjectName":"MySQL"},
... {"Name":"David","SubjectName":"C++"}
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e8836d3987b6e0e9d18f577")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo507.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5e8836d3987b6e0e9d18f577"),
"Information" : [
{
"Name" : "John",
"SubjectName" : "MySQL"
},
{
"Name" : "Bob",
"SubjectName" : "MongoDB"
},
{
"Name" : "Chris",
"SubjectName" : "MySQL"
},
{
"Name" : "David",
"SubjectName" : "C++"
}
]
}以下是用于过滤对象中某些字段的查询-
> db.demo507.aggregate([
... {$match: {"Information.SubjectName" : "MySQL" } },
... {$project: {
... _id:0,
... Information: {
... $filter: {
... input: '$Information',
... as: 'result',
... cond: {$eq: ['$$result.SubjectName', 'MySQL']}
... }
... }
... }
... },{$project: {Information: { SubjectName:1}}}
... ]);这将产生以下输出-
{ "Information" : [ { "SubjectName" : "MySQL" }, { "SubjectName" : "MySQL" } ] }