Nested lists are not handled

[LexanRed]

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 :(

[bnasslahsen]

@LexanRed,

The generated OpenAPI spec is correct.

If you are having issues with the UI, please raise a bug in the https://github.com/swagger-api/swagger-ui project instead

[LexanRed]

@bnasslahsen

The generated OpenAPI spec is only correct if I declare the List as ArrayList.
Instead of
private List<CourseDraftNodeResponse> children = new ArrayList<>();
I have to use
private ArrayList<CourseDraftNodeResponse> children = new ArrayList<>();

Only then the list is included in the generated spec. This only applies to lists, which are of the same class as the class they are defined in.

Sorry for making it not clear in my first post.
I hardly think this is working as intended.

[bnasslahsen]

@LexanRed,

The screenshot above, is related to the declaration with List
Two things here:

• if you are having an issue, add a failing testcase to your code that shows it.
• Second point, make sure that you are not referring to a bug in the swagger-core itself. As i can tell you 100% there is no difference of the processing in the springdoc-openapi code between List and ArrayList.

[LexanRed]

Second point, make sure that you are not referring to a bug in the swagger-core itself. As i can tell you 100% there is no difference of the processing in the springdoc-openapi code between List and ArrayList

Exactly this is the point. If declared as List, it is not present. If declared as ArrayList, it is processed correctly

[LexanRed]

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

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

[gyimgabor]

Is there any information about what causing this issue? I have a similar issue:

In the example below, the B type does contains the list, but the C and D do not.

• Adding additional properties or changing the name of the property in C or D does not fixes the issue.
• Using ArrayList instead of List, or using @ArraySchema annotation does not fixes the issue.

I am using springdoc-openapi-maven-plugin 1.4

@Data
public class A implements Serializable {

    @Data
    public class B implements Serializable {
        public String functionName;
        public List<A> arguments;
    }

    @Data
    public class C implements Serializable {
        public List<A> elements;
    }

    @Data
    public class D implements Serializable {
        public List<A> children;
    }
    public B b;
    public C c;
    public D d;
}