在MongoDB的子数组子数组中提取元素？
为了拉一个元素，使用$沿着拉$（位置）运算符。让我们创建一个包含文档的集合-
> db.demo679.insertOne(
... {
... id:1,
... "details": [
... {
... CountryName:"US",
... "information": [
...
... { "Name": "Chris", "FirstName": "Name=Chris" },
...
... {"Name": "Bob", "FirstName": "Name=Bob" }
... ]
... },
... {
... CountryName:"UK",
... "information": [
...
... { "Name": "Robert", "FirstName": "Name=Robert" },
...
... {"Name": "Sam", "FirstName": "Name=Sam" }
... ]
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea442cf04263e90dac943fd")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo679.find();
这将产生以下输出-
{ "_id" : ObjectId("5ea442cf04263e90dac943fd"), "id" : 1, "details" : [
{ "CountryName" : "US", "information" : [
{ "Name" : "Chris", "FirstName" : "Name=Chris" },
{ "Name" : "Bob", "FirstName" : "Name=Bob" }
] },
{ "CountryName" : "UK", "information" : [
{ "Name" : "Robert", "FirstName" : "Name=Robert" },
{ "Name" : "Sam", "FirstName" : "Name=Sam" }
] }
] }以下是查询以在MongoDB的子数组的子数组中提取元素-
> db.demo679.update(
... { "details.CountryName":"US" },
... { $pull: { 'details.$.information': { "Name" : "Bob", "FirstName" : "Name=Bob" } } }
... );
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })在find()方法的帮助下显示集合中的所有文档-
> db.demo679.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5ea442cf04263e90dac943fd"),
"id" : 1,
"details" : [
{
"CountryName" : "US",
"information" : [
{
"Name" : "Chris",
"FirstName" : "Name=Chris"
}
]
},
{
"CountryName" : "UK",
"information" : [
{
"Name" : "Robert",
"FirstName" : "Name=Robert"
},
{
"Name" : "Sam",
"FirstName" : "Name=Sam"
}
]
}
]
}