Fix #2686: @JsonBackReference not working with Builder

Author: JacksonJang

src/main/java/tools/jackson/databind/deser/BeanDeserializerFactory.java

@@ -274,7 +274,9 @@ public ValueDeserializer<Object> buildBeanDeserializer(DeserializationContext ct
         addObjectIdReader(ctxt, beanDescRef, builder);
 
         // managed/back reference fields/setters need special handling... first part
-        addBackReferenceProperties(ctxt, beanDescRef, builder);
+        // [databind#2686]: targetType For Builder pattern, this method is not using.
+        // So this value is null.
+        addBackReferenceProperties(ctxt, beanDescRef, builder, null);
         addInjectables(ctxt, beanDescRef, builder);
 
         final DeserializationConfig config = ctxt.getConfig();
@@ -334,7 +336,8 @@ protected ValueDeserializer<Object> buildBuilderBasedDeserializer(
         addObjectIdReader(ctxt, builderDescRef, builder);
 
         // managed/back reference fields/setters need special handling... first part
-        addBackReferenceProperties(ctxt, builderDescRef, builder);
+        // [databind#2686]: For Builder pattern, pass target type so that back-reference
+        addBackReferenceProperties(ctxt, builderDescRef, builder, valueType);
         addInjectables(ctxt, builderDescRef, builder);
 
         JsonPOJOBuilder.Value builderConfig = ctxt.getAnnotationIntrospector()
@@ -736,7 +739,8 @@ && isIgnorableType(ctxt, property, rawPropertyType, ignoredTypes)) {
      * and if so add them to bean, to be linked during resolution phase.
      */
     protected void addBackReferenceProperties(DeserializationContext ctxt,
-            BeanDescription.Supplier beanDescRef, BeanDeserializerBuilder builder)
+            BeanDescription.Supplier beanDescRef, BeanDeserializerBuilder builder,
+            JavaType targetType)
     {
         // and then back references, not necessarily found as regular properties
         List<BeanPropertyDefinition> refProps = beanDescRef.get().findBackReferences();
@@ -764,8 +768,31 @@ protected void addBackReferenceProperties(DeserializationContext ctxt,
                             refProp.getName());
                 }
                 String refName = refProp.findReferenceName();
-                builder.addBackReferenceProperty(refName, constructSettableProperty(ctxt,
-                        beanDescRef, refProp, refProp.getPrimaryType()));
+                SettableBeanProperty backRefProp;
+
+                if (targetType != null) {
+                    // [databind#2686]: Handle Builder
+                    backRefProp = constructBuilderBackRefProperty(ctxt,
+                            targetType, refProp);
+                } else {
+                    // normal
+                    backRefProp = constructSettableProperty(ctxt,
+                            beanDescRef, refProp, refProp.getPrimaryType());
+                }
+
+                if (backRefProp != null) {
+                    builder.addBackReferenceProperty(refName, backRefProp);
+                } else {
+                    if (targetType != null) {
+                        ctxt.reportBadTypeDefinition(beanDescRef,
+                                "Cannot find back-reference field '%s' in target type '%s' for Builder-based deserialization",
+                                refProp.getName(), targetType.getRawClass().getName());
+                    } else {
+                        ctxt.reportBadTypeDefinition(beanDescRef,
+                                "Cannot resolve back-reference property '%s'",
+                                refProp.getName());
+                    }
+                }
             }
         }
     }
@@ -1068,4 +1095,28 @@ protected void _validateSubType(DeserializationContext ctxt, JavaType type,
     {
         SubTypeValidator.instance().validateSubType(ctxt, type, beanDescRef);
     }
+
+    /**
+     * Helper method for constructing back-reference property when using Builder pattern.
+     *
+     * @since 3.1
+     */
+    protected SettableBeanProperty constructBuilderBackRefProperty(DeserializationContext ctxt,
+            JavaType targetType, BeanPropertyDefinition builderRefProp)
+    {
+        BeanDescription.Supplier targetDescRef = ctxt.lazyIntrospectBeanDescription(targetType);
+        BeanDescription targetDesc = targetDescRef.get();
+
+        // find back reference with same field
+        String propName = builderRefProp.getName();
+        for (BeanPropertyDefinition propDef : targetDesc.findProperties()) {
+            if (propName.equals(propDef.getName()) && propDef.hasField()) {
+                AnnotatedField field = propDef.getField();
+                JavaType propertyType = field.getType();
+                return constructSettableProperty(ctxt, targetDescRef, propDef, propertyType);
+            }
+        }
+
+        return null;
+    }
 }

…nd/tofix/BuilderWithBackRef2686Test.java …d/struct/BuilderWithBackRef2686Test.javasrc/test/java/tools/jackson/databind/tofix/BuilderWithBackRef2686Test.java renamed to src/test/java/tools/jackson/databind/struct/BuilderWithBackRef2686Test.java src/test/java/tools/jackson/databind/tofix/BuilderWithBackRef2686Test.java renamed to src/test/java/tools/jackson/databind/struct/BuilderWithBackRef2686Test.java

@@ -1,4 +1,4 @@
-package tools.jackson.databind.tofix;
+package tools.jackson.databind.struct;
 
 import java.beans.ConstructorProperties;
 
@@ -11,7 +11,6 @@
 import tools.jackson.databind.annotation.JsonDeserialize;
 import tools.jackson.databind.annotation.JsonPOJOBuilder;
 import tools.jackson.databind.testutil.DatabindTestUtil;
-import tools.jackson.databind.testutil.failure.JacksonTestFailureExpected;
 
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 
@@ -91,7 +90,6 @@ Content build() {
 
     private final ObjectMapper MAPPER = newJsonMapper();
 
-    @JacksonTestFailureExpected
     @Test
     void buildWithBackRefs2686() throws Exception {
         Container container = new Container();