MongoDB查询以从文档中提取特定值
要提取特定值，请对$pull使用UPDATE。让我们创建一个包含文档的集合-
> db.demo318.insertOne({Subject:["MySQL","MongoDB","Java"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e50ea6df8647eb59e562062")
}
> db.demo318.insertOne({Subject:["Spring","Hibernate"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e50ea78f8647eb59e562063")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo318.find();
这将产生以下输出-
{ "_id" : ObjectId("5e50ea6df8647eb59e562062"), "Subject" : [ "MySQL", "MongoDB", "Java" ] }
{ "_id" : ObjectId("5e50ea78f8647eb59e562063"), "Subject" : [ "Spring", "Hibernate" ] }以下是查询以$pull作为特定值“休眠”-
> db.demo318.update({Subject:"Hibernate"},{$pull:{"Subject":"Hibernate"}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })在find()方法的帮助下显示集合中的所有文档-
> db.demo318.find();
这将产生以下输出-
{ "_id" : ObjectId("5e50ea6df8647eb59e562062"), "Subject" : [ "MySQL", "MongoDB", "Java" ] }
{ "_id" : ObjectId("5e50ea78f8647eb59e562063"), "Subject" : [ "Spring" ] }