MongoDB嵌入式对象没有ID(空值) [英] MongoDB Embedded Objects have no ID (null value)
问题描述
我对使用Spring Data的MongoDB有疑问。
我有这些域类:
I have a question regarding MongoDB with Spring Data. I have these domain classes:
@Document
public class Deal {
@Id
private ObjectId _id;
private Location location;
private User user;
private String description;
private String title;
private String price;
private boolean approved;
private Date expirationDate;
private Date publishedDate;
}
@Document
public class Location {
@Id
private ObjectId _id;
private Double latitude;
private Double longitude;
private String country;
private String street;
private String zip;
}
@Document
public class User {
@Id
private ObjectId _id;
private String email;
private String password;
private String profile_image_url;
private Collection<Deal> deals = new ArrayList<Deal>();
}
通过这些域名,我可以成功CRUD。只有一个问题。保存具有交易的用户时,将交易和位置在将它们保存到MongoDB时将其设置为空。
为什么MongoDB不能为嵌入对象生成唯一的id?
With these domains I can successfully CRUD. There is only one problem. When saving a User with Deals, the deals and Location get _id set to null when saving them to MongoDB. Why can´t MongoDB generate unique id´s for embedded objects?
用一笔交易保存用户后的结果:
The result after saving a User with one deal:
{ "_id" : ObjectId( "4fed0591d17011868cf9c982" ),
"_class" : "User",
"email" : "milo@gmail.com",
"password" : "mimi",
"deals" : [
{ "_id" : null,
"location" : { "_id" : null,
"latitude" : 2.22,
"longitude" : 3.23445,
"country" : "Denmark",
"street" : "Denmark road 77",
"zip" : "2933" },
"description" : "The new Nexus 7 Tablet. A 7 inch tablet from Google.",
"title" : "Nexus 7",
"price" : "1300",
"approved" : false,
"expirationDate" : Date( 1343512800000 ),
"publishedDate" : Date( 1340933521374 ) } ] }
从结果中可以看出,交易和位置ID设置为NULL。
As you can see from the result, Deal and Location ID is set to NULL.
推荐答案
MongoDB CRUD操作(插入
,更新
, 查找
,删除
)所有操作都只能在顶级文档上运行 - 当然,您可以按嵌入字段过滤文档。嵌入式文档始终在父文档中返回。
MongoDB CRUD operations (insert
, update
, find
, remove
) all operate on top-level documents exclusively -- although of course you can filter by fields in embedded documents. Embedded documents are always returned within the parent document.
_id
字段是父文档的必填字段,并且通常不需要或存在于嵌入式文档中。如果您需要唯一标识符,您当然可以创建它们,如果方便您的代码或心智模型,您可以使用 _id
字段来存储它们;更典型地,它们以它们代表的内容命名(例如username,otherSystemKey等)。除了顶级文档之外,MongoDB本身或任何驱动程序都不会自动填充 _id
字段。
The _id
field is a required field of the parent document, and is typically not necessary or present in embedded documents. If you require a unique identifier, you can certainly create them, and you may use the _id
field to store them if that is convenient for your code or your mental model; more typically, they are named after what they represent (e.g. "username", "otherSystemKey", etc). Neither MongoDB itself, nor any of the drivers will automatically populate an _id
field except on the top-level document.
特别是在Java中,如果您希望为嵌入式文档中的 _id
字段生成ObjectId值,您可以使用:
Specifically in Java, if you wish to generate ObjectId values for the _id
field in embedded documents, you can do so with:
someEmbeddedDoc._id = new ObjectId();
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