MongoDB用位置运算符拉？
在MongoDB中将$pull运算符与位置运算符（$）一起使用。首先让我们创建一个包含文档的集合-
> db.pullWithPositionalOperatorDemo.insertOne(
... {
... _id: 100,
... "StudentDetails": [
... {
... "StudentId": "STU-1",
... "StudentFavouriteSubject": ["MongoDB", "Java"]
... },
... {
... "StudentId": "STU-2",
... "StudentFavouriteSubject": ["PHP", "MySQL"]
... }
... ]
... }
... );
{ "acknowledged" : true, "insertedId" : 100 }以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.pullWithPositionalOperatorDemo.find().pretty();
这将产生以下输出-
{
"_id" : 100,
"StudentDetails" : [
{
"StudentId" : "STU-1",
"StudentFavouriteSubject" : [
"MongoDB",
"Java"
]
},
{
"StudentId" : "STU-2",
"StudentFavouriteSubject" : [
"PHP",
"MySQL"
]
}
]
}以下是使用位置运算符执行拉取的查询-
> db.pullWithPositionalOperatorDemo.update({
... "StudentDetails" : {
... "$elemMatch" : {
... "StudentId" : "STU-2",
... "StudentFavouriteSubject" : "MySQL"
... }
... }
... }, {
... $pull : {
... "StudentDetails.$.StudentFavouriteSubject" : "MySQL"
... }
... }, {
... multi : true
... });
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })让我们再次检查上述集合中的所有文档-
> db.pullWithPositionalOperatorDemo.find().pretty();
这将产生以下输出-
{
"_id" : 100,
"StudentDetails" : [
{
"StudentId" : "STU-1",
"StudentFavouriteSubject" : [
"MongoDB",
"Java"
]
},
{
"StudentId" : "STU-2",
"StudentFavouriteSubject" : [
"PHP"
]
}
]
}