如何在 MongoDB 的嵌套数组中提取特定元素?
mongodbdatabasebig data analytics更新于 2026/1/11 22:22:17
要提取 MongoDB 中的特定元素，可以使用 $elemMatch 运算符。首先，我们创建一个包含文档的集合 −
> db.particularElementDemo.insertOne(
{
"GroupId" :"Group-1",
"UserDetails" : [
{
"UserName" : "John",
"UserOtherDetails" : [
{
"UserEmailId" : "John123@gmail.com",
"UserFriendName" : [
{
"Name" : "Chris"
}
]
},
{
"UserEmailId" : "John22@hotmail.com",
"UserFriendName" : [
{
"Name" : "Robert"
}
]
}
]
}
]
}
);
{ "acknowledged" : true, "insertedId" : 100 }
> db.particularElementDemo.find().pretty();
{
"_id" : 100,
"GroupId" : "Group-1",
"UserDetails" : [
{
"UserName" : "John",
"UserOtherDetails" : [
{
"UserEmailId" : "John123@gmail.com",
"UserFriendName" : [
{
"Name" : "Chris"
}
]
},
{
"UserEmailId" : "John22@hotmail.com",
"UserFriendName" : [
{
"Name" : "Robert"
}
]
}
]
}
]
}
借助 find() 方法显示集合中的所有文档 −
> db.particularElementDemo.find().pretty();
这将产生以下输出 −
{
"_id" : 100,
"GroupId" : "Group-1",
"UserDetails" : [
{
"UserName" : "John",
"UserOtherDetails" : [
{
"UserEmailId" : "John123@gmail.com",
"UserFriendName" : [
{
"Name" : "Chris"
}
]
},
{
"UserEmailId" : "John22@hotmail.com",
"UserFriendName" : [
{
"Name" : "Robert"
}
]
}
]
}
]
}
以下是在 MongoDB 嵌套数组中提取特定元素的查询 −
> db.particularElementDemo.find(
{
'UserDetails':{
$elemMatch:{
'UserOtherDetails':{
$elemMatch:{
'UserFriendName':{ $elemMatch: {"Name" : "Robert" } }
}
}
}
}
},{"UserDetails.UserOtherDetails.UserFriendName.Name":1}
);
这将产生以下输出 −
{ "_id" : 100, "UserDetails" : [ { "UserOtherDetails" : [ { "UserFriendName" : [ { "Name" : "Chris" } ] }, { "UserFriendName" : [ { "Name" : "Robert" } ] } ] } ] }
