在MongoDB聚合中的子集内应用条件？
要应用条件，请使用$setIsSubset。首先让我们创建一个包含文档的集合-
> db.subsetDemo.insertOne({"StudentName":"Chris","StudentFavouriteSubject":["Java","Python"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e063e49150ee0e76c06a052")
}
> db.subsetDemo.insertOne({"StudentName":"Chris","StudentFavouriteSubject":["Java","Python","MySQL"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e063e4f150ee0e76c06a053")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.subsetDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5e063e49150ee0e76c06a052"),
"StudentName" : "Chris",
"StudentFavouriteSubject" : [
"Java",
"Python"
]
}
{
"_id" : ObjectId("5e063e4f150ee0e76c06a053"),
"StudentName" : "Chris",
"StudentFavouriteSubject" : [
"Java",
"Python",
"MySQL"
]
}这是在MongoDB聚合子集中应用条件的查询-
> db.subsetDemo.aggregate([
... {
... $project: {
... _id: 0,
... StudentName: 1,
... isMySQL: {
... $setIsSubset: [["MySQL"], "$StudentFavouriteSubject"]
... }
... }
... }
... ]);这将产生以下输出-
{ "StudentName" : "Chris", "isMySQL" : false }
{ "StudentName" : "Chris", "isMySQL" : true }