为什么我应该将回购级别对象与控制器/服务级别对象混合？

Question

I worked on many microservices, and saw we dont mix repo level objects(mogo document, entity) with service/controller level request/response. I wanted to know more about it ? 1. We dont want pojo and entity/document to behave in same way?(Could be one reason) Please help me understanding reasons behind doing this.

Answer 1

If you need to separate entities (or persistence objects in general) and public interface responses (such as REST etc.) depends a lot on your application design.

If your persistence objects only contain simple, non-sensitive data, it is ok to use them for public interface responses as well. But here are some scenarios that would require separate objects:

1. Your persistence objects contain sensitive data (passwords, encryption keys, etc.) that is meant to be read by the outside. Then you would convert these objects into other types and stripping away that data to hide it from the public interface.

2. You have nested references in your persistence objects (relations between entities etc.) that reach very deep or even can form loops. If you would try to serialize these into a transport format (eg JSON), the process will fail because of the loop or your JSON object will be huge. Then it is easier to convert objects and removing the loops by just including IDs or whatever as your nested references.

In some applications I developed I even went one step further and settled on three different data object layers. The first layer is the persistence layer, could be entities, YAML or JSON representations or something like that.

Since the application uses a lot of different storage backends, and supports multiple for the same data, I convert these specific objects into general domain objects, which form the second layer.The application itself only works on these domain objects, never touching the persistence objects directly.

The third layer is the decorator layer that I use to hide or simplify information for output on my REST interface. They are used to counter the two scenarios mentioned above.

Answer 2

Definitely you could do that, especially in a small project or demo project.

Let's assume you are doing web application. For complex enterprise applications, most time you would like to expose certain fields and certain format of data, with one more attraction of data object, you can avoid change entity fields and database table fields.