Fixes #418 by adjusting the output for Links.

There is a custom serializer for the Links object which creates a sorted map
of all links. That map is then passed to jackson for serialization, thus some
manual work is needed to fix the schema.

Author: fredrik-w

springdoc-openapi-data-rest/src/main/java/org/springdoc/core/SpringDocDataRestConfiguration.java

@@ -18,26 +18,67 @@
 
 package org.springdoc.core;
 
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import io.swagger.v3.core.converter.AnnotatedType;
+import io.swagger.v3.core.converter.ModelConverters;
+import io.swagger.v3.core.converter.ResolvedSchema;
+import io.swagger.v3.core.util.Json;
+import io.swagger.v3.oas.annotations.media.Schema;
+import io.swagger.v3.oas.models.media.MapSchema;
+import io.swagger.v3.oas.models.media.ObjectSchema;
+import io.swagger.v3.oas.models.media.StringSchema;
 import org.springdoc.core.converters.PageableSupportConverter;
-
+import org.springdoc.core.customizers.OpenApiCustomiser;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.data.rest.core.config.RepositoryRestConfiguration;
+import org.springframework.hateoas.Link;
+import org.springframework.hateoas.Links;
+import org.springframework.hateoas.RepresentationModel;
+import org.springframework.hateoas.mediatype.hal.RepresentationModelMixin;
 
 import static org.springdoc.core.Constants.SPRINGDOC_ENABLED;
 
 @Configuration
 @ConditionalOnProperty(name = SPRINGDOC_ENABLED, matchIfMissing = true)
 public class SpringDocDataRestConfiguration {
 
-	@Bean
-	PageableSupportConverter pageableSupportConverter() {
-		return new PageableSupportConverter();
-	}
+    @Bean
+    PageableSupportConverter pageableSupportConverter() {
+        return new PageableSupportConverter();
+    }
+
+    @Bean
+    public HalProvider halProvider(RepositoryRestConfiguration repositoryRestConfiguration) {
+        return new HalProvider(repositoryRestConfiguration);
+    }
+
+	/**
+	 * Registers an OpenApiCustomiser and a jackson mixin to ensure the definition of `Links` matches the serialized
+	 * output. This is done because the customer serializer converts the data to a map before serializing it.
+	 *
+	 * @see org.springframework.hateoas.mediatype.hal.Jackson2HalModule.HalLinkListSerializer#serialize(Links, JsonGenerator, SerializerProvider)
+	 */
+    @Bean
+    public OpenApiCustomiser linksSchemaCustomiser(RepositoryRestConfiguration repositoryRestConfiguration) {
+        if (!repositoryRestConfiguration.useHalAsDefaultJsonMediaType()) {
+            return openApi -> {};
+        }
+        Json.mapper().addMixIn(RepresentationModel.class, RepresentationModelLinksOASMixin.class);
+        ResolvedSchema resolvedLinkSchema = ModelConverters.getInstance()
+                .resolveAsResolvedSchema(new AnnotatedType(Link.class));
+        return openApi -> openApi
+				.schema("Link", resolvedLinkSchema.schema)
+				.schema("Links", new MapSchema()
+						.additionalProperties(new StringSchema())
+						.additionalProperties(new ObjectSchema().$ref("#/components/schemas/Link")));
+    }
 
-	@Bean
-	public HalProvider halProvider(RepositoryRestConfiguration repositoryRestConfiguration) {
-		return new HalProvider(repositoryRestConfiguration);
-	}
+    static abstract class RepresentationModelLinksOASMixin extends RepresentationModelMixin {
+        @Override
+        @Schema(ref = "#/components/schemas/Links")
+        public abstract Links getLinks();
+    }
 }

springdoc-openapi-data-rest/src/test/resources/results/app2.json

@@ -123,23 +123,6 @@
   },
   "components": {
     "schemas": {
-      "CollectionModelEntityModelEmployee": {
-        "type": "object",
-        "properties": {
-          "_embedded": {
-            "type": "array",
-            "items": {
-              "$ref": "#/components/schemas/EntityModelEmployee"
-            }
-          },
-          "_links": {
-            "type": "array",
-            "items": {
-              "$ref": "#/components/schemas/Link"
-            }
-          }
-        }
-      },
       "Employee": {
         "type": "object",
         "properties": {
@@ -175,10 +158,27 @@
             "type": "string"
           },
           "_links": {
+            "$ref": "#/components/schemas/Links"
+          }
+        }
+      },
+      "Links": {
+        "type": "object",
+        "additionalProperties": {
+          "$ref": "#/components/schemas/Link"
+        }
+      },
+      "CollectionModelEntityModelEmployee": {
+        "type": "object",
+        "properties": {
+          "_embedded": {
             "type": "array",
             "items": {
-              "$ref": "#/components/schemas/Link"
+              "$ref": "#/components/schemas/EntityModelEmployee"
             }
+          },
+          "_links": {
+            "$ref": "#/components/schemas/Links"
           }
         }
       },

springdoc-openapi-data-rest/src/test/resources/results/app3.json

@@ -68,5 +68,7 @@
       }
     }
   },
-  "components": {}
+  "components": {
+    "schemas": {}
+  }
 }