#697 Add conflict resolution logic to SparkUtils.copyMetadata.

Author: yruslan

spark-cobol/src/main/scala/za/co/absa/cobrix/spark/cobol/utils/SparkUtils.scala

@@ -243,17 +243,26 @@ object SparkUtils extends Logging {
   /**
     * Copies metadata from one schema to another as long as names and data types are the same.
     *
-    * @param schemaFrom Schema to copy metadata from.
-    * @param schemaTo   Schema to copy metadata to.
-    * @param overwrite  If true, the metadata of schemaTo is not retained
+    * @param schemaFrom      Schema to copy metadata from.
+    * @param schemaTo        Schema to copy metadata to.
+    * @param overwrite       If true, the metadata of schemaTo is not retained
+    * @param sourcePreferred If true, schemaFrom metadata is used on conflicts, schemaTo otherwise.
     * @return Same schema as schemaTo with metadata from schemaFrom.
     */
-  def copyMetadata(schemaFrom: StructType, schemaTo: StructType, overwrite: Boolean = false): StructType = {
+  def copyMetadata(schemaFrom: StructType,
+                   schemaTo: StructType,
+                   overwrite: Boolean = false,
+                   sourcePreferred: Boolean = false): StructType = {
     def joinMetadata(from: Metadata, to: Metadata): Metadata = {
       val newMetadataMerged = new MetadataBuilder
 
-      newMetadataMerged.withMetadata(from)
-      newMetadataMerged.withMetadata(to)
+      if (sourcePreferred) {
+        newMetadataMerged.withMetadata(to)
+        newMetadataMerged.withMetadata(from)
+      } else {
+        newMetadataMerged.withMetadata(from)
+        newMetadataMerged.withMetadata(to)
+      }
 
       newMetadataMerged.build()
     }

spark-cobol/src/test/scala/za/co/absa/cobrix/spark/cobol/utils/SparkUtilsSuite.scala

@@ -626,6 +626,58 @@ class SparkUtilsSuite extends AnyFunSuite with SparkTestBase with BinaryFileFixt
     assert(newDf.schema.fields.head.metadata.getLong("maxLength") == 120)
   }
 
+  test("copyMetadata should retain metadata on conflicts by default") {
+    val df1 = List(1, 2, 3).toDF("col1")
+    val df2 = List(1, 2, 3).toDF("col1")
+
+    val metadata1 = new MetadataBuilder()
+    metadata1.putString("comment", "Test")
+    metadata1.putLong("maxLength", 100)
+
+    val metadata2 = new MetadataBuilder()
+    metadata2.putLong("maxLength", 120)
+    metadata2.putLong("newMetadata", 180)
+
+    val schema1WithMetadata = StructType(Seq(df1.schema.fields.head.copy(metadata = metadata1.build())))
+    val schema2WithMetadata = StructType(Seq(df2.schema.fields.head.copy(metadata = metadata2.build())))
+
+    val df1WithMetadata = spark.createDataFrame(df2.rdd, schema1WithMetadata)
+
+    val schemaWithMetadata = SparkUtils.copyMetadata(df1WithMetadata.schema, schema2WithMetadata)
+
+    val newDf = spark.createDataFrame(df2.rdd, schemaWithMetadata)
+
+    assert(newDf.schema.fields.head.metadata.getString("comment") == "Test")
+    assert(newDf.schema.fields.head.metadata.getLong("maxLength") == 120)
+    assert(newDf.schema.fields.head.metadata.getLong("newMetadata") == 180)
+  }
+
+  test("copyMetadata should overwrite metadata on conflicts when sourcePreferred=true") {
+    val df1 = List(1, 2, 3).toDF("col1")
+    val df2 = List(1, 2, 3).toDF("col1")
+
+    val metadata1 = new MetadataBuilder()
+    metadata1.putString("comment", "Test")
+    metadata1.putLong("maxLength", 100)
+
+    val metadata2 = new MetadataBuilder()
+    metadata2.putLong("maxLength", 120)
+    metadata2.putLong("newMetadata", 180)
+
+    val schema1WithMetadata = StructType(Seq(df1.schema.fields.head.copy(metadata = metadata1.build())))
+    val schema2WithMetadata = StructType(Seq(df2.schema.fields.head.copy(metadata = metadata2.build())))
+
+    val df1WithMetadata = spark.createDataFrame(df2.rdd, schema1WithMetadata)
+
+    val schemaWithMetadata = SparkUtils.copyMetadata(df1WithMetadata.schema, schema2WithMetadata, sourcePreferred = true)
+
+    val newDf = spark.createDataFrame(df2.rdd, schemaWithMetadata)
+
+    assert(newDf.schema.fields.head.metadata.getString("comment") == "Test")
+    assert(newDf.schema.fields.head.metadata.getLong("maxLength") == 100)
+    assert(newDf.schema.fields.head.metadata.getLong("newMetadata") == 180)
+  }
+
   test("copyMetadata should not retain original metadata when overwrite = true") {
     val df1 = List(1, 2, 3).toDF("col1")
     val df2 = List(1, 2, 3).toDF("col1")