How to show data to user with DTO - spring-boot

Question

This is the data that I am currently showing to the user:
{
"id": 3,
"name": "AB:11",
"description": "AB:11 is an Imperial Black Barley Wine brewed with ginger, black raspberries and chipotle peppers. A 12.8% rollercoaster of ginger zestiness and chipotle smokiness, all bound together with dark berry tartness and the decadent residual body of a Black Barley Wine.",
"method": {
"mash_temp": [
{
"temp": {
"value": 68,
"unit": "celsius"
}
}
]
}
And I don't need this "method" field. I tried to show data with DTO which looks like this:
public class Beer {
private Integer id;
private String name;
private String description;
private Method method;
private List<MashTemp> mashTemp;
private Temp temp;
// getters & setters
My DTO is giving me back a response like a:
"id": 1,
"name": "Bitch Please (w/ 3 Floyds)",
"description": "This limited edition American Barley Wine was brewed in collaboration with 3 Floyds Brewery. This beer had all the warm, boozy and smoky aspects of an Islay Scotch whisky with the sweet malt and devastatingly bitter attributes of a barley wine. Peat smoke features prominently, backed up with a complex fruity hop profile.",
"method": {
"mash_temp": [
{
"temp": {
"value": 65
}
}
]
},
"mashTemp": null,
"temp": null
Any Idea how to fix this?

Answer 1

You need the following classes:
public class BeerDto {
private Integer id;
private String name;
private String description;
private List<MashTempDto> mashTemp;
}
public class MashTempDto {
private TempDto temp;
}
public class TempDto {
private Integer value;
}
Now you need to map your original Beer object to BeerDto (the same is true for MashTempDto and TempDto) which you will then make available in your API.

Answer 2

I think this is a perfect use case for Blaze-Persistence Entity Views.
I created the library to allow easy mapping between JPA models and custom interface or abstract class defined models, something like Spring Data Projections on steroids. The idea is that you define your target structure(domain model) the way you like and map attributes(getters) via JPQL expressions to the entity model.
A DTO model for your use case could look like the following with Blaze-Persistence Entity-Views:
#EntityView(Beer.class)
public interface BeerDto {
#IdMapping
Integer getId();
String getName();
String getDescription();
Set<MashTempDto> getMashTemp();
#EntityView(MashTemp.class)
interface MashTempDto {
TempDto getTemp();
}
#EntityView(Temp.class)
interface TempDto {
Integer getValue();
}
}
Querying is a matter of applying the entity view to a query, the simplest being just a query by id.
BeerDto a = entityViewManager.find(entityManager, BeerDto.class, id);
The Spring Data integration allows you to use it almost like Spring Data Projections: https://persistence.blazebit.com/documentation/entity-view/manual/en_US/index.html#spring-data-features
Page<BeerDto> findAll(Pageable pageable);
The best part is, it will only fetch the state that is actually necessary!