从 MongoDB 中的单个数组元素取消设置属性？
使用$unset运算符取消设置属性。让我们首先创建一个包含文档的集合-
> db.unsetAnAttributeDemo.insertOne(
... {
... _id: 1,
... "StudentDetails": [
... {
... "StudentFirstName": "Ramit",
... "StudentCountryName":"UK"
... },
... {
... "StudentFirstName": "Bob",
... "StudentCountryName":"US"
... },
... {
... "StudentFirstName": "Carol",
... "StudentCountryName":"AUS"
...
... }
... ]
... }
... );
{ "acknowledged" : true, "insertedId" : 1 }以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.unsetAnAttributeDemo.find().pretty();
这将产生以下输出-
{
"_id" : 1,
"StudentDetails" : [
{
"StudentFirstName" : "Ramit",
"StudentCountryName" : "UK"
},
{
"StudentFirstName" : "Bob",
"StudentCountryName" : "US"
},
{
"StudentFirstName" : "Carol",
"StudentCountryName" : "AUS"
}
]
}以下是从单个数组元素取消设置属性的查询。值为“AUS”的属性“StudentCountryName”将取消设置-
> db.unsetAnAttributeDemo.update({"StudentDetails.StudentCountryName": "AUS"}, {$unset:
{"StudentDetails.$.StudentCountryName": 1}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })让我们显示集合中的文档，以检查是否清除了值为“AUS”的StudentCountryName属性-
> db.unsetAnAttributeDemo.find().pretty();
这将产生以下输出-
{
"_id" : 1,
"StudentDetails" : [
{
"StudentFirstName" : "Ramit",
"StudentCountryName" : "UK"
},
{
"StudentFirstName" : "Bob",
"StudentCountryName" : "US"
},
{
"StudentFirstName" : "Carol"
}
]
}