如何在MongoDB中删除数组的第n个元素？
您可以使用$unset以及$pull运算符进行更新，以删除数组的第n个元素。
让我们用文档创建一个集合。使用文档创建集合的查询如下-
> db.getNThElementDemo.insertOne({"UserName":"John","UserAge":23,"ListOfFriends":["Carol","Sam","Mike","Bob"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c94ee7516f542d757e2b43e")
}
> db.getNThElementDemo.insertOne({"UserName":"David","UserAge":21,"ListOfFriends":["Chris","Robert"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c94eeaa16f542d757e2b43f")
}在find()method的帮助下显示集合中的所有文档。查询如下-
> db.getNThElementDemo.find().pretty();
以下是输出-
{
"_id" : ObjectId("5c94ee7516f542d757e2b43e"),
"UserName" : "John",
"UserAge" : 23,
"ListOfFriends" : [
"Carol",
"Sam",
"Mike",
"Bob"
]
}
{
"_id" : ObjectId("5c94eeaa16f542d757e2b43f"),
"UserName" : "David",
"UserAge" : 21,
"ListOfFriends" : [
"Chris",
"Robert"
]
}这是删除数组的第n个元素的查询-
> db.getNThElementDemo.update({}, {$unset : {"ListOfFriends.2" : 1 }});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.getNThElementDemo.update({}, {$pull : {"ListOfFriends" : null}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })现在您可以检查数组中的第n个元素是否已删除。
查询如下-
> db.getNThElementDemo.find().pretty();
以下是输出-
{
"_id" : ObjectId("5c94ee7516f542d757e2b43e"),
"UserName" : "John",
"UserAge" : 23,
"ListOfFriends" : [
"Carol",
"Sam",
"Bob"
]
}
{
"_id" : ObjectId("5c94eeaa16f542d757e2b43f"),
"UserName" : "David",
"UserAge" : 21,
"ListOfFriends" : [
"Chris",
"Robert"
]
}