如何从MongoDB 2.4中的数组内的文档中删除属性
在MongoDB 2.4中使用本地Nodejs驱动程序，并尝试从embedded在数组中的文档中移除属性。 例如，我怎样才能删除所有文件embedded在gym 562e7c1ae6c3e8ce29abfe05 grades数组？ 所以从这个：
{ "_id" : ObjectId("562abaaffb5870b8fb9dca3f"), "grades" : [ { "_id" : ObjectId("562e7bbe70ee82bb290192bd"), "discipline" : "55aae5b7848b9c8bf4ecbb5c", "grade" : "55aae5b7848b9c8bf4ecbb4c", "gym" : "562e7c1ae6c3e8ce29abfe06", "registeredOn" : ISODate("2015-10-26T19:15:10.565Z") }, { "discipline" : "55aae5b7848b9c8bf4ecbb5c", "grade" : "55aae5b7848b9c8bf4ecbb4d", "gym" : "562e7c1ae6c3e8ce29abfe05", "registeredOn" : ISODate("2015-10-26T19:17:08.603Z"), "_id" : ObjectId("562e7c34e6c3e8ce29abfe06") }, { "discipline" : "55aae5b7848b9c8bf4ecbb5c", "grade" : "55aae5b7848b9c8bf4ecbb4d", "gym" : "562e7c1ae6c3e8ce29abfe05", "registeredOn" : ISODate("2015-10-26T19:17:08.603Z"), "_id" : ObjectId("562e7c34e6c3e8ce29abfe07") } ], }, { "_id" : ObjectId("562abaaffb5870b8fb9dca3f"), "grades" : [ { "_id" : ObjectId("562e7bbe70ee82bb290192bd"), "discipline" : "55aae5b7848b9c8bf4ecbb5c", "grade" : "55aae5b7848b9c8bf4ecbb4c", "gym" : "562e7c1ae6c3e8ce29abfe07", "registeredOn" : ISODate("2015-10-26T19:15:10.565Z") }, { "discipline" : "55aae5b7848b9c8bf4ecbb5c", "grade" : "55aae5b7848b9c8bf4ecbb4d", "gym" : "562e7c1ae6c3e8ce29abfe05", "registeredOn" : ISODate("2015-10-26T19:17:08.603Z"), "_id" : ObjectId("562e7c34e6c3e8ce29abfe06") } ], }
我需要这个：
{ "_id" : ObjectId("562abaaffb5870b8fb9dca3f"), "grades" : [ { "_id" : ObjectId("562e7bbe70ee82bb290192bd"), "discipline" : "55aae5b7848b9c8bf4ecbb5c", "grade" : "55aae5b7848b9c8bf4ecbb4c", "gym" : "562e7c1ae6c3e8ce29abfe06", "registeredOn" : ISODate("2015-10-26T19:15:10.565Z") }, { "discipline" : "55aae5b7848b9c8bf4ecbb5c", "grade" : "55aae5b7848b9c8bf4ecbb4d", "registeredOn" : ISODate("2015-10-26T19:17:08.603Z"), "_id" : ObjectId("562e7c34e6c3e8ce29abfe06") }, { "discipline" : "55aae5b7848b9c8bf4ecbb5c", "grade" : "55aae5b7848b9c8bf4ecbb4d", "registeredOn" : ISODate("2015-10-26T19:17:08.603Z"), "_id" : ObjectId("562e7c34e6c3e8ce29abfe07") } ], }, { "_id" : ObjectId("562abaaffb5870b8fb9dca3f"), "grades" : [ { "_id" : ObjectId("562e7bbe70ee82bb290192bd"), "discipline" : "55aae5b7848b9c8bf4ecbb5c", "grade" : "55aae5b7848b9c8bf4ecbb4c", "gym" : "562e7c1ae6c3e8ce29abfe07", "registeredOn" : ISODate("2015-10-26T19:15:10.565Z") }, { "discipline" : "55aae5b7848b9c8bf4ecbb5c", "grade" : "55aae5b7848b9c8bf4ecbb4d", "registeredOn" : ISODate("2015-10-26T19:17:08.603Z"), "_id" : ObjectId("562e7c34e6c3e8ce29abfe06") } ], }
下面的查询将只删除第一个与我指定的id匹配的文档。 "_id" : ObjectId("562e7c34e6c3e8ce29abfe07")的第二个文件仍然会有健身房属性562e7c1ae6c3e8ce29abfe05 。 multi似乎是多余的，那么是否有任何方法来删除所有健身房属性与我指定的ID？
collections.users.update({ "grades.gym": "562e7c1ae6c3e8ce29abfe05" }, { $unset: { "grades.$.gym": "562e7c1ae6c3e8ce29abfe05" } }, { multi: true })
最好使用.find()返回游标，使用.each()方法遍历它，以访问符合条件的集合中的每个文档，从而获得数组字段，删除与条件匹配的属性并更新文件，如下所示：
collection.find({ "grades.gym": "562e7c1ae6c3e8ce29abfe05" }).each(function(err, doc){ // handle err var new_grades = doc.grades.map(function (grade){ if (grade.gym == "562e7c1ae6c3e8ce29abfe05") { delete grade.gym; } return grade; }); collection.update({ "_id": doc._id },{ "$set": { "grades": new_grades }}); });