MongoDB的“ $ and”运算符用于子集合来获取文档？
要获取文档，请在MongoDB中使用$in代替$and。首先让我们创建一个包含文档的集合-
> db.demo83.insertOne(
... {
... "Details":[
... {
... "Name":"Chris",
... "Subject":[
... "MySQL",
... "MongoDB"
... ]
... },
... {
... "Name":"David",
... "Subject":[
... "Java",
... "C"
... ]
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bfd2271bf0181ecc422a3")
}
> db.demo83.insertOne(
... {
... "Details":[
... {
... "Name":"Bob",
... "Subject":[
... "C++",
... "Python"
... ]
... },
... {
... "Name":"John",
... "Subject":[
... "Spring",
... "Hibernate"
... ]
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bfd4571bf0181ecc422a4")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo83.find();
这将产生以下输出-
{
"_id" : ObjectId("5e2bfd2271bf0181ecc422a3"), "Details" : [
{ "Name" : "Chris", "Subject" : [ "MySQL", "MongoDB" ] },
{ "Name" : "David", "Subject" : [ "Java", "C" ] }
]
}
{
"_id" : ObjectId("5e2bfd4571bf0181ecc422a4"), "Details" : [
{ "Name" : "Bob", "Subject" : [ "C++", "Python" ] },
{ "Name" : "John", "Subject" : [ "Spring", "Hibernate" ] }
]
}以下是使用$in查找文档的查询-
> db.demo83.find({ "Details" : { "$elemMatch" : {"Name" :"Chris" , "Subject":{"$in":["MongoDB"]}}}});这将产生以下输出-
{
"_id" : ObjectId("5e2bfd2271bf0181ecc422a3"), "Details" : [
{ "Name" : "Chris", "Subject" : [ "MySQL", "MongoDB" ] },
{ "Name" : "David", "Subject" : [ "Java", "C" ] }
]
}