Nested lists are not handled

Describe the bug We have a simple DTO mapping which includes a list objects of the same data type. This is the class:

@Data
@Builder
@AllArgsConstructor(access = AccessLevel.PRIVATE)
@Schema(name = "CourseDraftNode")
public class CourseDraftNodeResponse implements Comparable<CourseDraftNodeResponse> {

    @NotNull
    private UUID key;
    @NotNull
    private OffsetDateTime createdAt;
    @NotNull
    private OffsetDateTime updatedAt;

    private UUID parentKey;
    @NotNull
    private UUID draftKey;

    @NotNull
    private CourseNodeType type;
    @NotNull
    private Integer position;
    @NotNull
    private String title;
    private String description;

    @NotNull
    private List<CourseDraftNodeItemResponse> items = new ArrayList<>();
    @NotNull
    private List<CourseDraftNodeResponse> children = new ArrayList<>();

    @Override
    public int compareTo(CourseDraftNodeResponse otherNodeResponse) {
        // Sort by parentKey nulls first and then by position
        if (Objects.isNull(parentKey) && Objects.nonNull(otherNodeResponse.getParentKey())) {
            return -1;
        } else if (Objects.nonNull(parentKey) && Objects.isNull(otherNodeResponse.getParentKey())) {
            return 1;
        } else {
            return position.compareTo(otherNodeResponse.getPosition());
        }
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof CourseDraftNodeResponse that)) return false;
        return getKey().equals(that.getKey());
    }

    @Override
    public int hashCode() {
        return Objects.hash(getKey());
    }
}

The list children is not included in the generated json. The list items is visible, but not children. We tried other classes and added Lists. Whenever we want to add a list with the same data type as the object to model a tree structure, the list is not present in the generated api specification.

This is how the the class looks like if you inspect it with swagger ui.

If I change the type from List to ArrayList in the response DTO, the list is added to the generated JSON.

In the swagger UI it is displayed as a list of strings… this is really a strange behaviour.

To Reproduce Steps to reproduce the behavior: Create a class which contains a list of the same data type as the class itself. Create a rest endpoint which returns this an object of this class. Inspect the generated JSON and the swagger UI.

• What version of spring-boot you are using? 2.7.4

• What modules and versions of springdoc-openapi are you using?

<dependency>
    <groupId>org.springdoc</groupId>
    <artifactId>springdoc-openapi-ui</artifactId>
    <version>1.6.11</version>
</dependency>
<dependency>
    <groupId>org.springdoc</groupId>
    <artifactId>springdoc-openapi-security</artifactId>
    <version>1.6.11</version>
</dependency>
<dependency>
    <groupId>org.springdoc</groupId>
    <artifactId>springdoc-openapi-data-rest</artifactId>
    <version>1.6.11</version>
</dependency>

• What is the actual and the expected result using OpenAPI Description (yml or json)? json

• Provide with a sample code (HelloController) or Test that reproduces the problem

@RestController
@Tag(name = "Course Draft")
@RequestMapping("/test")
@RequiredArgsConstructor
public class TestController {
    @GetMapping
    public CourseDraftNodeResponse getCourseDraft() {
        return CourseDraftNodeResponse.builder().build();
    }
}

Expected behavior The nested list should be added to the json response. Swagger should display not string as data type but the actual object.

Additional context Lombok is used.

[LReinacher]

we are facing the same issue 😦

[LexanRed]

Annotating the list with @ArraySchema seems to fix the problem. The generated JSON looks fine.

@ArraySchema
private List<CourseNodeResponse> children = new ArrayList<>();