Revert "Revert "Disallow complex types as keys for nested types in arrays""

This reverts commit bb42d0c6f30de25b9ca6b8e232b6920aeb51a7d1.

Reason for system tests failing was changes in the system tests, not
this PR.

1 files changed, 8 insertions, 1 deletions

diff --git a/document/src/main/java/com/yahoo/document/json/JsonSerializationHelper.java b/document/src/main/java/com/yahoo/document/json/JsonSerializationHelper.java
index 8e934001381..afe14cf1e6a 100644
--- a/document/src/main/java/com/yahoo/document/json/JsonSerializationHelper.java
+++ b/document/src/main/java/com/yahoo/document/json/JsonSerializationHelper.java
@@ -2,9 +2,11 @@
 package com.yahoo.document.json;
 
 import com.fasterxml.jackson.core.JsonGenerator;
+import com.yahoo.document.DataType;
 import com.yahoo.document.DocumentId;
 import com.yahoo.document.Field;
 import com.yahoo.document.PositionDataType;
+import com.yahoo.document.PrimitiveDataType;
 import com.yahoo.document.datatypes.Array;
 import com.yahoo.document.datatypes.ByteFieldValue;
 import com.yahoo.document.datatypes.CollectionFieldValue;
@@ -186,7 +188,12 @@ public class JsonSerializationHelper {
             generator.writeStartObject();
 
             for (Map.Entry<K, V> entry : map.entrySet()) {
-                generator.writeFieldName(entry.getKey().toString());
+                K key = entry.getKey();
+                DataType keyType = key.getDataType();
+                if ( ! (keyType instanceof PrimitiveDataType)) {
+                    throw new IllegalArgumentException("Can't use complex types as keys for map fields. Type: " + keyType);
+                }
+                generator.writeFieldName(key.toString());
                 entry.getValue().serialize(null, fieldWriter);
             }