dongjoon-hyun commented on a change in pull request #24158: [SPARK-26847][SQL] 
Pruning nested serializers from object serializers: MapType support
URL: https://github.com/apache/spark/pull/24158#discussion_r268033297
 
 

 ##########
 File path: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/objects.scala
 ##########
 @@ -132,49 +130,74 @@ object ObjectSerializerPruning extends Rule[LogicalPlan] 
{
         fields.map(f => collectStructType(f.dataType, structs))
       case ArrayType(elementType, _) =>
         collectStructType(elementType, structs)
+      case MapType(_, valueType, _) =>
+        // Because we can't select a field from struct in key, so we skip key 
type.
+        collectStructType(valueType, structs)
       case _ =>
     }
     structs
   }
 
+  /**
+   * This method returns pruned `CreateNamedStruct` expression given an 
original `CreateNamedStruct`
+   * and a pruned `StructType`.
+   */
+  private def pruneNamedStruct(struct: CreateNamedStruct, prunedType: 
StructType) = {
+    // Filters out the pruned fields.
+    val prunedFields = struct.nameExprs.zip(struct.valExprs).filter { case 
(nameExpr, _) =>
+      val name = nameExpr.eval(EmptyRow).toString
+      prunedType.fieldNames.exists { fieldName =>
+        if (SQLConf.get.caseSensitiveAnalysis) {
+          fieldName.equals(name)
+        } else {
+          fieldName.equalsIgnoreCase(name)
+        }
+      }
+    }.flatMap(pair => Seq(pair._1, pair._2))
+
+    CreateNamedStruct(prunedFields)
+  }
+
+  /**
+   * When we change nested serializer data type, `If` expression will be 
unresolved because
+   * literal null's data type doesn't match now. We need to align it with new 
data type.
+   * Note: we should do `transformUp` explicitly to change data types.
+   */
+  private def alignNullTypeInIf(expr: Expression) = expr.transformUp {
+    case i @ If(_: IsNull, Literal(null, dt), ser) if 
!dt.sameType(ser.dataType) =>
 
 Review comment:
   ~Do you have a test case for this?~ Sorry, I realized that this is just a 
refactoring.

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