set parent for train validation split

Author: sethah

mllib/src/main/scala/org/apache/spark/ml/tuning/TrainValidationSplit.scala

@@ -221,7 +221,7 @@ class TrainValidationSplitModel private[ml] (
       uid,
       bestModel.copy(extra).asInstanceOf[Model[_]],
       validationMetrics.clone())
-    copyValues(copied, extra)
+    copyValues(copied, extra).setParent(parent)
   }
 
   @Since("2.0.0")

mllib/src/test/scala/org/apache/spark/ml/tuning/TrainValidationSplitSuite.scala

@@ -22,11 +22,11 @@ import org.apache.spark.ml.{Estimator, Model}
 import org.apache.spark.ml.classification.{LogisticRegression, LogisticRegressionModel}
 import org.apache.spark.ml.classification.LogisticRegressionSuite.generateLogisticInput
 import org.apache.spark.ml.evaluation.{BinaryClassificationEvaluator, Evaluator, RegressionEvaluator}
-import org.apache.spark.ml.linalg.{DenseMatrix, Vectors}
+import org.apache.spark.ml.linalg.Vectors
 import org.apache.spark.ml.param.ParamMap
 import org.apache.spark.ml.param.shared.HasInputCol
 import org.apache.spark.ml.regression.LinearRegression
-import org.apache.spark.ml.util.DefaultReadWriteTest
+import org.apache.spark.ml.util.{DefaultReadWriteTest, MLTestingUtils}
 import org.apache.spark.mllib.util.{LinearDataGenerator, MLlibTestSparkContext}
 import org.apache.spark.sql.Dataset
 import org.apache.spark.sql.types.StructType
@@ -78,6 +78,10 @@ class TrainValidationSplitSuite
       .setTrainRatio(0.5)
       .setSeed(42L)
     val cvModel = cv.fit(dataset)
+
+    // copied model must have the same paren.
+    MLTestingUtils.checkCopy(cvModel)
+
     val parent = cvModel.bestModel.parent.asInstanceOf[LinearRegression]
     assert(parent.getRegParam === 0.001)
     assert(parent.getMaxIter === 10)