Fixed #370

Author: cowtowncoder

release-notes/VERSION

@@ -12,6 +12,8 @@ Version: 2.3.1 (xx-Dec-2013)
  (reported by jknack@github)
 #367: Make `TypeNameIdResolver` call `TypeResolver` for resolving base type
  (suggested by Ben F)
+#370: Fail to add Object Id for POJO with no properties
+ (reported by jh3141@github)
 - Fix for [jackson-module-afterburner#38]: need to remove @JacksonStdImpl from
   `RawSerializer`, to avoid accidental removal of proper handling.
 

src/main/java/com/fasterxml/jackson/databind/ser/BeanSerializerBuilder.java

@@ -170,15 +170,15 @@ public boolean hasProperties() {
     public JsonSerializer<?> build()
     {
         BeanPropertyWriter[] properties;
-        // No properties or any getter? No real serializer; caller gets to handle
+        // No properties, any getter or object id writer?
+        // No real serializer; caller gets to handle
         if (_properties == null || _properties.isEmpty()) {
-            if (_anyGetter == null) {
+            if (_anyGetter == null && _objectIdWriter == null) {
                 return null;
             }
             properties = NO_PROPERTIES;
         } else {
             properties = _properties.toArray(new BeanPropertyWriter[_properties.size()]);
-            
         }
         return new BeanSerializer(_beanDesc.getType(), this,
                 properties, _filteredProperties);

src/main/java/com/fasterxml/jackson/databind/ser/BeanSerializerFactory.java

@@ -435,7 +435,7 @@ protected JsonSerializer<Object> constructBeanSerializer(SerializerProvider prov
         }
 
         JsonSerializer<Object> ser = (JsonSerializer<Object>) builder.build();
-
+        
         /* However, after all modifications: no properties, no serializer
          * (note; as per [JACKSON-670], check was moved later on from an earlier location)
          */

src/test/java/com/fasterxml/jackson/databind/struct/TestObjectIdSerialization.java

@@ -4,7 +4,6 @@
 import com.fasterxml.jackson.annotation.JsonIdentityReference;
 import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 import com.fasterxml.jackson.annotation.ObjectIdGenerators;
-
 import com.fasterxml.jackson.databind.*;
 
 /**
@@ -146,7 +145,11 @@ static class Broken
         public int value;
         public int customId;
     }
-    
+
+    // [Issue#370]
+    @JsonIdentityInfo(generator=ObjectIdGenerators.IntSequenceGenerator.class, property="@id")
+    public static class EmptyObject { }
+
     /*
     /*****************************************************
     /* Unit tests, external id serialization
@@ -155,7 +158,7 @@ static class Broken
 
     private final static String EXP_SIMPLE_INT_CLASS = "{\"id\":1,\"value\":13,\"next\":1}";
 
-    private final ObjectMapper MAPPER = new ObjectMapper();
+    private final ObjectMapper MAPPER = objectMapper();
 
     public void testSimpleSerializationClass() throws Exception
     {
@@ -187,6 +190,14 @@ public void testSimpleSerializationProperty() throws Exception
         assertEquals(EXP_SIMPLE_INT_PROP, json);
     }
 
+    // [Issue#370]
+    public void testEmptyObjectWithId() throws Exception
+    {
+        final ObjectMapper mapper = new ObjectMapper();
+        String json = mapper.writeValueAsString(new EmptyObject());
+        assertEquals(aposToQuotes("{'@id':1}"), json);
+    }    
+
     /*
     /*****************************************************
     /* Unit tests, custom (property) id serialization