您可以使用 $pull 运算符从 MongoDB 中的数组中删除对象。为了理解这个概念,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.removeObjectFromArrayDemo.insertOne( ... { ... ... "StudentName": "John", ... "StudentAcademicProjectDetails": ... [{ ... "StudentProjectId": 101, ... "StudentProjectName": "Pig Dice Game" ... }, ... { ... "StudentProjectId": 110, ... "StudentProjectName": "Library Management System" ... }, ... ... { ... "StudentProjectId": 120, ... "StudentProjectName": "Phonebook Management System" ... } ... ] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5c8ad13d6cea1f28b7aa0817") }
在find()方法的帮助下显示集合中的所有文档。查询如下 -
> db.removeObjectFromArrayDemo.find().pretty();
以下是输出 -
{ "_id" : ObjectId("5c8ad13d6cea1f28b7aa0817"), "StudentName" : "John", "StudentAcademicProjectDetails" : [ { "StudentProjectId" : 101, "StudentProjectName" : "Pig Dice Game" }, { "StudentProjectId" : 110, "StudentProjectName" : "Library Management System" }, { "StudentProjectId" : 120, "StudentProjectName" : "Phonebook Management System" } ] }
这是从 MongoDB 中的数组中删除对象的查询 -
> db.removeObjectFromArrayDemo.update( ... {'_id': ObjectId("5c8ad13d6cea1f28b7aa0817")}, ... { $pull: { "StudentAcademicProjectDetails" : { StudentProjectId: 101 } } }, ... false, ... true ... ); WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
让我们检查集合中的文档以检查对象是否已从数组中删除。查询如下 -
> db.removeObjectFromArrayDemo.find().pretty();
以下是输出 -
{ "_id" : ObjectId("5c8ad13d6cea1f28b7aa0817"), "StudentName" : "John", "StudentAcademicProjectDetails" : [ { "StudentProjectId" : 110, "StudentProjectName" : "Library Management System" }, { "StudentProjectId" : 120, "StudentProjectName" : "Phonebook Management System" } ] }
查看上面的示例输出,删除了 101 的字段“StudentProjectId”。