Domain Driven Design

I want to share a little code about some develop that I did, applying concepts of DDD Domain Driven Design. My focus was to construct an aggregate root class called Building, that controls all the flow below them, as the following diagram:

Here, as I explained in the first paragraph, all the changes must happend through the aggregate root class; so in that case, we can have a consistent hierarchy, without any danger of uncontrolled change.

Model

I used JPA to model the domain. As Hibernate suggested in the best practices of JPA because of its efficient way of generating sql, I based all the relationships in bidirectional ways.

There is some attention point when i want to save a floor passing as parameter an uuid from a building. Because of the bidirectional relationship, hibernate load all floors of that building before saveing the new floor; that will be catastrophic speaking about performance. So i had an idea about not to force a bidirectional relantionship when i wanted just to save and not to load elements. This made me think about the architecture pattern CQRS Command Query Responsability Segregation, in order to uste differente objects to write and to read. I will speak about this in the next episode.

Exception

I mostly treated the exception inside de Domain because i applyied DDD. I use a Controller Advice class, called InformationControllerAdvice.java where i defined all the exceptions in the application, wrapping the response in new objects with some interesting information as error code, http error code, and a message error loaded from a specific file.

Endpoints

As i mentioned before, i tried to mantain a data consistency, so all of the entities in the application depends on their aggregate root entity. Nothing can change from outside this aggregate root.

Test

I developed some tests using Rest Assured to guaranteed the APIs from the beginning to the response of the endpoint.

Curls

Im shearing some curls to test the application

Building

curl --location --request POST 'localhost:8080/api/v1/building' \
--header 'Content-Type: application/json' \
--data-raw '{
    "name": "Classic",
    "address": "Rua 10 de Setembro",
    "floors": [
        {
            "number": 1,
            "apartments": [
                {
                    "number": 11            
                },
                {
                    "number": 12            
                },
                {
                    "number": 13            
                }
                ,{
                    "number": 14            
                }
            ]
        },
         {
            "number": 2,
            "apartments": [
                {
                    "number": 21            
                },
                {
                    "number": 22            
                },
                {
                    "number": 23            
                }
                ,{
                    "number": 24            
                }
            ]
        },
        {
            "number": 3,
            "apartments": [
                {
                    "number": 31            
                },           
                {
                    "number": 32            
                },
                {
                    "number": 33            
                }
                ,{
                    "number": 34            
                }
            ]
        }
    ]
}'

curl --location --request GET 'localhost:8080/api/v1/building/{{uuid}}'

Floor

curl --location --request POST 'localhost:8080/api/v1/building/{{uuid}}/floor' \
--header 'Content-Type: application/json' \
--data-raw '{
    "number": 4,
    "apartments": [
        {
            "number": 41         
        },
        {
            "number": 42            
        },
        {
            "number": 43            
        }
        ,{
            "number": 44            
        }
    ]
}'

curl --location --request GET 'localhost:8080/api/v1/building/{{uuid}}/floor/4'

Aparments

curl --location --request POST 'localhost:8080/api/v1/building/{{uuid}}/floor/2/apartment' \
--header 'Content-Type: application/json' \
--data-raw '{
    "number":2
}'

curl --location --request GET 'localhost:8080/api/v1/building/{{uuid}}/floor/2/apartment/1'

Articles

Martin Fowler's page

DDD Community