Issue with JsonTypeInfo and Lists

When I try and serialize a list of objects that have JsonTypeInfo defined, the objects in the list do not have the JsonTypeInfo property set. I am having problems with this against both 1.9.4 and 2.0.2, if there is a way to do this that I missed in the documentation, please let me know.

diff --git a/src/test/java/com/fasterxml/jackson/databind/jsontype/TestAbstractTypeNames.java b/src/test/java/com/fasterxml/jackson/databind/jsontype/TestAbstractTypeNames.java
index 5a257a1..57213b4 100644
--- a/src/test/java/com/fasterxml/jackson/databind/jsontype/TestAbstractTypeNames.java
+++ b/src/test/java/com/fasterxml/jackson/databind/jsontype/TestAbstractTypeNames.java
@@ -9,6 +9,8 @@ import com.fasterxml.jackson.annotation.JsonTypeInfo.Id;

 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.ObjectMapper.DefaultTyping;
+import com.fasterxml.jackson.databind.node.ArrayNode;
+import com.fasterxml.jackson.databind.node.ObjectNode;

 /**
  * Unit tests for checking how combination of interfaces, implementation
@@ -93,6 +95,21 @@ public class TestAbstractTypeNames  extends BaseMapTest
     /**********************************************************
      */

+    public void testCollection() throws Exception
+    {
+        ObjectMapper mapper = new ObjectMapper();
+        List<DefaultEmployee> friends = new ArrayList<DefaultEmployee>();
+        friends.add(new DefaultEmployee("Joe Hildebrandt", null, "MDA"));
+
+        String singleObject = mapper.writeValueAsString(friends.get(0));
+        ObjectNode output = mapper.readValue(singleObject, ObjectNode.class);
+        assertEquals("Employee", output.get("userType").asText());
+
+        String list = mapper.writeValueAsString(friends);
+        ArrayNode listOutput = mapper.readValue(list, ArrayNode.class);
+        assertNotNull("Expected " + listOutput.get(0) + " to include userType", listOutput.get(0).get("userType"));
+    }
+
     // Testing [JACKSON-498], partial fix
     public void testEmptyCollection() throws Exception
     {

[cowtowncoder]

@ilgrosso Actually this is due to type-erasure: what Jackson sees is a List<?>, and since ? in there can only be considered same as java.lang.Object, no type information is included (as there is no @JsonTypeInfo in java.lang.Object definition. There are ways to get around that:

1. Provide explicit root type (construct an ObjectWriter with JavaType for List<Child1>)
2. Create sub-class of List that is not generic; like class ChildList extends ArrayList<Child1> { }, pass that

and if so, generic types of List can be determined correctly to produce expected output. So there is no bug with this handling (unless one consider Java’s Type Erasure to be bug; but that’s not something I can do anything about).

At this point I will close this bug as descriptions and comments have been bouncing to various things; let’s open new specific entries for specific remaining problems (with 2.2.2 and above).

[galcyurio]

private ObjectMapper mObjectMapper;
private ObjectWriter mObjectWriter;

...

mObjectMapper = new ObjectMapper();
mObjectWriter = mObjectMapper.writerFor(mObjectMapper.getTypeFactory().constructCollectionType(List.class, MyClass.class));

MyClass myClass = new MyClass(...);
mObjectMapper.writeValueAsString(myClass);
mObjectWriter.writeValueAsstring(myClass);

[{"answer":"asdf"},{"answers":[1,2,3]}]
[{"type":"shortTextResult","answer":"asdf"},{"type":"choiceResult","answers":[1,2,3]}]

I solved likely above, but I cannot assume that this is best practice…