Spring Data Mongodb-用于收集不同类型的存储库 [英] Spring Data Mongodb - repository for collection with different types

问题描述

我有一个mongo集合，其中可能包含我映射到Java类型的三种类型的实体:

I have a mongo collection that may contain three types of entities that I map to java types:

• 节点
• LeafType1
• LeafType2

使用父项中的子节点的dbRefs收集以存储树状结构.

Collection is ment to store tree-like structure using dbRefs of child nodes in parent entry.

我没有在Spring参考文档中找到有关主题的任何信息，所以我在这里问:是否可以使用Repository机制处理可能包含不同类型对象的集合?

I didn't find any information about subject in Spring reference documentation so I'm asking here: Is there a way to use Repository mechanism to work with collection that may contain different types of objects?

在一个集合中声明多个用于不同类型的存储库似乎不是一个好主意，因为我经常遇到这样的情况:查询的对象不是预期的类型，并且为抽象类创建一个所有可能的类型继承都不起作用的存储库

Declaring several repositories for different types in one collection seems like not very good idea because I always struggle with situations when queried object is not of expected type and creating one repository for abstract class that all possible types inherrit doesn't seems to work.

为了说明我的意思:

/**
 * This seems not safe
 */
public interface NodeRepository extends MongoRepository<Node, String> { }
public interface LeafType1Repository extends MongoRepository<LeafType1, String> { }
public interface LeafType2Repository extends MongoRepository<LeafType2, String> { }

/**
 * This doesn't work at all
 */
public interface MyCollectionRepository extends MongoRepository<AbstractMyCollectionNode, String> { }

推荐答案

如果Node \ LeafType1 \ LeafType2是AbstractMyCollectionNode的子类，那么事情就容易了.只需像编写时那样声明存储库:

If Node\LeafType1\LeafType2 are sub-classes of AbstractMyCollectionNode, then things will be easy. Just declare the repository like you write:

public interface MyCollectionRepository extends MongoRepository<AbstractMyCollectionNode, String> { }

我们已经在一个项目中做到了这一点，并且效果很好. Spring Data将在mongodb集合中的文档中添加一个名为"_class"的属性，以便可以指出要实例化的类.

We have done this in a project, and it works good. Spring Data will add an property named '_class' to the documents in mongodb collection, so that it can finger out which class to instantiate.

存储在一个集合中的文档可能有一些相似之处，也许您可​​以为它们提取一个通用类.

Documents that stored in one collection may have some similarity, maybe you can extract a generic class for them.

以下是从我们的一个项目中复制的一些代码:

Here are some code copied from one of our projects:

实体:

public abstract class Document {
    private String id;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }
    ....

---

public class WebClipDocument extends Document {
    private String digest;
    ...

存储库:

public interface DocumentDao extends MongoRepository<Document, String>{
...

并且，如果您在mongodb集合中的文档不具有"_class"属性.您可以使用转换器:

And, if your documents in mongodb collection does not have the "_class" property. You can use Converter:

在存储和查询对象时，让MongoConverter实例处理所有Java类型到DBObject的映射很方便.但是，有时您可能希望"MongoConverter"完成大部分工作，但允许您有选择地处理特定类型的转换或优化性能.

When storing and querying your objects it is convenient to have a MongoConverter instance handle the mapping of all Java types to DBObjects. However, sometimes you may want the `MongoConverter’s do most of the work but allow you to selectively handle the conversion for a particular type or to optimize performance.

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