Ensure that HalConfiguration MediaTypeConfigurationCustomizers are al…

…ways run

spring-data-rest is not aware of the existence of MediaTypeConfigurationCustomizer, so it does not apply the configuration when pulling the HalConfiguration bean directly.
This leads to the configuration settings in HalConfiguration inconsistently being applied, depending on if a setting is used in spring-hateoas or spring-data-rest.

Always applying all customizers directly in a BeanPostProcessor ensures that the HalConfiguration bean itself has all the customizations directly baked-in,
and does not require all consumers to be aware of MediaTypeConfigurationCustomizer

contentgrid-spring-boot-autoconfigure/src/main/java/com/contentgrid/spring/boot/autoconfigure/data/web/ContentGridSpringDataRestAutoConfiguration.java

@@ -9,6 +9,8 @@
 import com.contentgrid.spring.data.rest.problem.ContentGridProblemDetailsConfiguration;
 import com.contentgrid.spring.data.rest.validation.ContentGridSpringDataRestValidationConfiguration;
 import com.contentgrid.spring.data.rest.webmvc.ContentGridSpringDataRestProfileConfiguration;
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.beans.factory.config.BeanPostProcessor;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
@@ -22,6 +24,9 @@
 import org.springframework.data.rest.webmvc.ContentGridRestProperties;
 import org.springframework.data.rest.webmvc.ContentGridSpringDataRestConfiguration;
 import org.springframework.data.rest.webmvc.config.RepositoryRestMvcConfiguration;
+import org.springframework.hateoas.mediatype.MediaTypeConfigurationCustomizer;
+import org.springframework.hateoas.mediatype.MediaTypeConfigurationFactory;
+import org.springframework.hateoas.mediatype.hal.HalConfiguration;
 
 @AutoConfiguration
 @ConditionalOnBean(RepositoryRestMvcConfiguration.class)
@@ -54,6 +59,21 @@ ContentGridRestProperties contentGridRestProperties() {
         return new ContentGridRestProperties();
     }
 
+    @Bean
+    static BeanPostProcessor contentGridApplyHalConfigurationCustomizers(
+            ObjectProvider<MediaTypeConfigurationCustomizer<HalConfiguration>> customizers
+    ) {
+        return new BeanPostProcessor() {
+            @Override
+            public Object postProcessAfterInitialization(Object bean, String beanName) {
+                if (bean instanceof HalConfiguration halConfiguration) {
+                    return new MediaTypeConfigurationFactory<>(() -> halConfiguration, customizers).getConfiguration();
+                }
+                return bean;
+            }
+        };
+    }
+
     @ConditionalOnBean(CurieProviderCustomizer.class)
     @Import({
             ContentGridCurieConfiguration.class,

contentgrid-spring-data-rest/src/test/java/com/contentgrid/spring/data/rest/hal/forms/ContentGridHalFormsConfigurationTest.java

@@ -3,6 +3,7 @@
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 import com.contentgrid.spring.test.fixture.invoicing.InvoicingApplication;
@@ -233,4 +234,23 @@ void updateFormFieldForConstrainedAttributeOptions() throws Exception {
         );
     }
 
+    @Test
+    void relationAndContentIsAlwaysArray() throws Exception {
+        var createdCustomer = mockMvc.perform(
+                        post("/customers").contentType(MediaType.APPLICATION_JSON).content("""
+                                {
+                                    "vat": "BE123"
+                                }
+                                """))
+                .andExpect(status().isCreated())
+                .andReturn()
+                .getResponse()
+                .getHeader("Location");
+
+        mockMvc.perform(get(createdCustomer).accept(MediaTypes.HAL_FORMS_JSON))
+                .andExpect(jsonPath("$._links['cg:content']").isArray())
+                .andExpect(jsonPath("$._links['cg:relation']").isArray())
+        ;
+    }
+
 }