Fix entity mapping issue for the parent-child entity fetching with pagination test case

Author: vladmihalcea

core/src/test/java/com/vladmihalcea/book/hpjp/hibernate/fetching/FetchEntitiesWithPaginationTest.java

@@ -0,0 +1,49 @@
+package com.vladmihalcea.book.hpjp.hibernate.fetching.pagination;
+
+import com.vladmihalcea.book.hpjp.hibernate.identifier.Identifiable;
+import org.hibernate.transform.BasicTransformerAdapter;
+
+import java.io.Serializable;
+import java.util.*;
+
+/**
+ * @author Vlad Mihalcea
+ */
+public class DistinctPostResultTransformer extends BasicTransformerAdapter {
+
+    public static final DistinctPostResultTransformer INSTANCE = new DistinctPostResultTransformer();
+
+    @Override
+    public List transformList(List list) {
+        Map<Serializable, Identifiable> identifiableMap = new LinkedHashMap<>(list.size());
+        for (Object entityArray : list) {
+            if (Object[].class.isAssignableFrom(entityArray.getClass())) {
+                Post post = null;
+                PostComment comment = null;
+
+                Object[] tuples = (Object[]) entityArray;
+
+                for (Object tuple : tuples) {
+                    if (tuple instanceof Post) {
+                        post = (Post) tuple;
+                    } else if (tuple instanceof PostComment) {
+                        comment = (PostComment) tuple;
+                    } else {
+                        throw new UnsupportedOperationException(
+                                "Tuple " + tuple.getClass() + " is not supported!"
+                        );
+                    }
+                }
+                Objects.requireNonNull(post);
+                Objects.requireNonNull(comment);
+
+                if (!identifiableMap.containsKey(post.getId())) {
+                    identifiableMap.put(post.getId(), post);
+                    post.setComments(new ArrayList<>());
+                }
+                post.addComment(comment);
+            }
+        }
+        return new ArrayList<>(identifiableMap.values());
+    }
+}