the-other-tim-brown commented on code in PR #17475:
URL: https://github.com/apache/hudi/pull/17475#discussion_r2593938002


##########
hudi-spark-datasource/hudi-spark-common/src/main/scala/org/apache/spark/sql/avro/HoodieSchemaInternalConverters.scala:
##########
@@ -0,0 +1,236 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.avro
+
+import org.apache.hudi.HoodieSchemaConverters
+import org.apache.hudi.common.schema.{HoodieSchema, HoodieSchemaField, 
HoodieSchemaType}
+
+import org.apache.spark.annotation.DeveloperApi
+import org.apache.spark.sql.types._
+
+import scala.collection.JavaConverters._
+
+/**
+ * This object contains methods that are used to convert HoodieSchema to Spark 
SQL schemas and vice versa.
+ *
+ * NOTE: This provides direct conversion between HoodieSchema and Spark 
DataType
+ * without going through Avro Schema intermediary.
+ */
+
+@DeveloperApi
+private[sql] object HoodieSchemaInternalConverters extends 
HoodieSchemaConverters {
+
+  /**
+   * Internal wrapper for SQL data type and nullability.
+   */
+  case class SchemaType(dataType: DataType, nullable: Boolean)
+
+  override def toSqlType(hoodieSchema: HoodieSchema): (DataType, Boolean) = {
+    val result = toSqlTypeHelper(hoodieSchema, Set.empty)
+    (result.dataType, result.nullable)
+  }
+
+  override def toHoodieType(catalystType: DataType, nullable: Boolean, 
recordName: String, nameSpace: String): HoodieSchema = {
+    val schema = catalystType match {
+      // Primitive types
+      case BooleanType => HoodieSchema.create(HoodieSchemaType.BOOLEAN)
+      case ByteType | ShortType | IntegerType => 
HoodieSchema.create(HoodieSchemaType.INT)
+      case LongType => HoodieSchema.create(HoodieSchemaType.LONG)
+      case DateType => HoodieSchema.createDate()
+      case TimestampType => HoodieSchema.createTimestampMicros()
+      case TimestampNTZType => HoodieSchema.createLocalTimestampMicros()
+      case FloatType => HoodieSchema.create(HoodieSchemaType.FLOAT)
+      case DoubleType => HoodieSchema.create(HoodieSchemaType.DOUBLE)
+      case StringType | _: CharType | _: VarcharType => 
HoodieSchema.create(HoodieSchemaType.STRING)
+      case NullType => HoodieSchema.create(HoodieSchemaType.NULL)
+      case BinaryType => HoodieSchema.create(HoodieSchemaType.BYTES)
+
+      case d: DecimalType =>
+        HoodieSchema.createDecimal(d.precision, d.scale)
+
+      // Complex types
+      case ArrayType(elementType, containsNull) =>
+        val elementSchema = toHoodieType(elementType, containsNull, 
recordName, nameSpace)
+        HoodieSchema.createArray(elementSchema)
+
+      case MapType(StringType, valueType, valueContainsNull) =>
+        val valueSchema = toHoodieType(valueType, valueContainsNull, 
recordName, nameSpace)
+        HoodieSchema.createMap(valueSchema)
+
+      case st: StructType =>
+        val childNameSpace = if (nameSpace != "") s"$nameSpace.$recordName" 
else recordName
+
+        // Check if this might be a union (using heuristic like Avro converter)
+        if (canBeUnion(st)) {
+          val nonNullUnionFieldTypes = st.map { f =>
+            toHoodieType(f.dataType, nullable = false, f.name, childNameSpace)
+          }
+          val unionFieldTypes = if (nullable) {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            types.add(HoodieSchema.create(HoodieSchemaType.NULL))
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          } else {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          }
+          HoodieSchema.createUnion(unionFieldTypes)
+        } else {
+          // Create record
+          val fields = st.map { f =>
+            val fieldSchema = toHoodieType(f.dataType, f.nullable, f.name, 
childNameSpace)
+            val doc = if (f.metadata.contains("comment")) 
f.metadata.getString("comment") else null
+            HoodieSchemaField.of(f.name, fieldSchema, doc)
+          }
+
+          val fieldsJava = new java.util.ArrayList[HoodieSchemaField]()
+          fields.foreach(fieldsJava.add)
+
+          HoodieSchema.createRecord(recordName, nameSpace, null, fieldsJava)
+        }
+
+      case other => throw new IncompatibleSchemaException(s"Unexpected Spark 
DataType: $other")
+    }
+
+    // Wrap with null union if nullable (and not already a union)
+    if (nullable && catalystType != NullType && schema.getType != 
HoodieSchemaType.UNION) {
+      HoodieSchema.createNullable(schema)
+    } else {
+      schema
+    }
+  }
+
+  private def toSqlTypeHelper(hoodieSchema: HoodieSchema, existingRecordNames: 
Set[String]): SchemaType = {
+    hoodieSchema.getType match {
+      // Primitive types
+      case HoodieSchemaType.INT => SchemaType(IntegerType, nullable = false)
+      case HoodieSchemaType.STRING => SchemaType(StringType, nullable = false)
+      case HoodieSchemaType.BOOLEAN => SchemaType(BooleanType, nullable = 
false)
+      case HoodieSchemaType.BYTES => SchemaType(BinaryType, nullable = false)
+      case HoodieSchemaType.DOUBLE => SchemaType(DoubleType, nullable = false)
+      case HoodieSchemaType.FLOAT => SchemaType(FloatType, nullable = false)
+      case HoodieSchemaType.LONG => SchemaType(LongType, nullable = false)
+      case HoodieSchemaType.NULL => SchemaType(NullType, nullable = true)
+      case HoodieSchemaType.ENUM => SchemaType(StringType, nullable = false)
+
+      // Logical types
+      case HoodieSchemaType.DATE =>
+        SchemaType(DateType, nullable = false)
+
+      case HoodieSchemaType.TIMESTAMP =>
+        hoodieSchema match {
+          case ts: HoodieSchema.Timestamp =>
+            if (ts.isUtcAdjusted) {
+              SchemaType(TimestampType, nullable = false)
+            } else {
+              SchemaType(TimestampNTZType, nullable = false)
+            }
+          case _ =>
+            // Fallback for non-specialized timestamp schema
+            SchemaType(TimestampType, nullable = false)
+        }
+
+      case HoodieSchemaType.DECIMAL =>
+        hoodieSchema match {
+          case dec: HoodieSchema.Decimal =>
+            SchemaType(DecimalType(dec.getPrecision, dec.getScale), nullable = 
false)
+          case _ =>
+            throw new IncompatibleSchemaException(
+              s"DECIMAL type must be HoodieSchema.Decimal instance, got: 
${hoodieSchema.getClass}")
+        }
+
+      case HoodieSchemaType.FIXED =>
+        // FIXED can be either binary or decimal with logical type

Review Comment:
   Fixed cannot be a decimal. A Hoodie Schema will only have one type



##########
hudi-spark-datasource/hudi-spark-common/src/main/scala/org/apache/spark/sql/avro/HoodieSchemaInternalConverters.scala:
##########
@@ -0,0 +1,236 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.avro
+
+import org.apache.hudi.HoodieSchemaConverters
+import org.apache.hudi.common.schema.{HoodieSchema, HoodieSchemaField, 
HoodieSchemaType}
+
+import org.apache.spark.annotation.DeveloperApi
+import org.apache.spark.sql.types._
+
+import scala.collection.JavaConverters._
+
+/**
+ * This object contains methods that are used to convert HoodieSchema to Spark 
SQL schemas and vice versa.
+ *
+ * NOTE: This provides direct conversion between HoodieSchema and Spark 
DataType
+ * without going through Avro Schema intermediary.
+ */
+
+@DeveloperApi
+private[sql] object HoodieSchemaInternalConverters extends 
HoodieSchemaConverters {
+
+  /**
+   * Internal wrapper for SQL data type and nullability.
+   */
+  case class SchemaType(dataType: DataType, nullable: Boolean)
+
+  override def toSqlType(hoodieSchema: HoodieSchema): (DataType, Boolean) = {
+    val result = toSqlTypeHelper(hoodieSchema, Set.empty)
+    (result.dataType, result.nullable)
+  }
+
+  override def toHoodieType(catalystType: DataType, nullable: Boolean, 
recordName: String, nameSpace: String): HoodieSchema = {
+    val schema = catalystType match {
+      // Primitive types
+      case BooleanType => HoodieSchema.create(HoodieSchemaType.BOOLEAN)
+      case ByteType | ShortType | IntegerType => 
HoodieSchema.create(HoodieSchemaType.INT)
+      case LongType => HoodieSchema.create(HoodieSchemaType.LONG)
+      case DateType => HoodieSchema.createDate()
+      case TimestampType => HoodieSchema.createTimestampMicros()
+      case TimestampNTZType => HoodieSchema.createLocalTimestampMicros()
+      case FloatType => HoodieSchema.create(HoodieSchemaType.FLOAT)
+      case DoubleType => HoodieSchema.create(HoodieSchemaType.DOUBLE)
+      case StringType | _: CharType | _: VarcharType => 
HoodieSchema.create(HoodieSchemaType.STRING)
+      case NullType => HoodieSchema.create(HoodieSchemaType.NULL)
+      case BinaryType => HoodieSchema.create(HoodieSchemaType.BYTES)
+
+      case d: DecimalType =>
+        HoodieSchema.createDecimal(d.precision, d.scale)
+
+      // Complex types
+      case ArrayType(elementType, containsNull) =>
+        val elementSchema = toHoodieType(elementType, containsNull, 
recordName, nameSpace)
+        HoodieSchema.createArray(elementSchema)
+
+      case MapType(StringType, valueType, valueContainsNull) =>
+        val valueSchema = toHoodieType(valueType, valueContainsNull, 
recordName, nameSpace)
+        HoodieSchema.createMap(valueSchema)
+
+      case st: StructType =>
+        val childNameSpace = if (nameSpace != "") s"$nameSpace.$recordName" 
else recordName
+
+        // Check if this might be a union (using heuristic like Avro converter)
+        if (canBeUnion(st)) {
+          val nonNullUnionFieldTypes = st.map { f =>
+            toHoodieType(f.dataType, nullable = false, f.name, childNameSpace)
+          }
+          val unionFieldTypes = if (nullable) {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            types.add(HoodieSchema.create(HoodieSchemaType.NULL))
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          } else {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          }
+          HoodieSchema.createUnion(unionFieldTypes)
+        } else {
+          // Create record
+          val fields = st.map { f =>
+            val fieldSchema = toHoodieType(f.dataType, f.nullable, f.name, 
childNameSpace)
+            val doc = if (f.metadata.contains("comment")) 
f.metadata.getString("comment") else null
+            HoodieSchemaField.of(f.name, fieldSchema, doc)
+          }
+
+          val fieldsJava = new java.util.ArrayList[HoodieSchemaField]()
+          fields.foreach(fieldsJava.add)
+
+          HoodieSchema.createRecord(recordName, nameSpace, null, fieldsJava)
+        }
+
+      case other => throw new IncompatibleSchemaException(s"Unexpected Spark 
DataType: $other")
+    }
+
+    // Wrap with null union if nullable (and not already a union)
+    if (nullable && catalystType != NullType && schema.getType != 
HoodieSchemaType.UNION) {
+      HoodieSchema.createNullable(schema)
+    } else {
+      schema
+    }
+  }
+
+  private def toSqlTypeHelper(hoodieSchema: HoodieSchema, existingRecordNames: 
Set[String]): SchemaType = {
+    hoodieSchema.getType match {
+      // Primitive types
+      case HoodieSchemaType.INT => SchemaType(IntegerType, nullable = false)
+      case HoodieSchemaType.STRING => SchemaType(StringType, nullable = false)
+      case HoodieSchemaType.BOOLEAN => SchemaType(BooleanType, nullable = 
false)
+      case HoodieSchemaType.BYTES => SchemaType(BinaryType, nullable = false)
+      case HoodieSchemaType.DOUBLE => SchemaType(DoubleType, nullable = false)
+      case HoodieSchemaType.FLOAT => SchemaType(FloatType, nullable = false)
+      case HoodieSchemaType.LONG => SchemaType(LongType, nullable = false)
+      case HoodieSchemaType.NULL => SchemaType(NullType, nullable = true)
+      case HoodieSchemaType.ENUM => SchemaType(StringType, nullable = false)

Review Comment:
   Let's group this with the `STRING` case



##########
hudi-spark-datasource/hudi-spark-common/src/main/scala/org/apache/spark/sql/avro/HoodieSchemaInternalConverters.scala:
##########
@@ -0,0 +1,236 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.avro
+
+import org.apache.hudi.HoodieSchemaConverters
+import org.apache.hudi.common.schema.{HoodieSchema, HoodieSchemaField, 
HoodieSchemaType}
+
+import org.apache.spark.annotation.DeveloperApi
+import org.apache.spark.sql.types._
+
+import scala.collection.JavaConverters._
+
+/**
+ * This object contains methods that are used to convert HoodieSchema to Spark 
SQL schemas and vice versa.
+ *
+ * NOTE: This provides direct conversion between HoodieSchema and Spark 
DataType
+ * without going through Avro Schema intermediary.
+ */
+
+@DeveloperApi
+private[sql] object HoodieSchemaInternalConverters extends 
HoodieSchemaConverters {
+
+  /**
+   * Internal wrapper for SQL data type and nullability.
+   */
+  case class SchemaType(dataType: DataType, nullable: Boolean)
+
+  override def toSqlType(hoodieSchema: HoodieSchema): (DataType, Boolean) = {
+    val result = toSqlTypeHelper(hoodieSchema, Set.empty)
+    (result.dataType, result.nullable)
+  }
+
+  override def toHoodieType(catalystType: DataType, nullable: Boolean, 
recordName: String, nameSpace: String): HoodieSchema = {
+    val schema = catalystType match {
+      // Primitive types
+      case BooleanType => HoodieSchema.create(HoodieSchemaType.BOOLEAN)
+      case ByteType | ShortType | IntegerType => 
HoodieSchema.create(HoodieSchemaType.INT)
+      case LongType => HoodieSchema.create(HoodieSchemaType.LONG)
+      case DateType => HoodieSchema.createDate()
+      case TimestampType => HoodieSchema.createTimestampMicros()
+      case TimestampNTZType => HoodieSchema.createLocalTimestampMicros()
+      case FloatType => HoodieSchema.create(HoodieSchemaType.FLOAT)
+      case DoubleType => HoodieSchema.create(HoodieSchemaType.DOUBLE)
+      case StringType | _: CharType | _: VarcharType => 
HoodieSchema.create(HoodieSchemaType.STRING)
+      case NullType => HoodieSchema.create(HoodieSchemaType.NULL)
+      case BinaryType => HoodieSchema.create(HoodieSchemaType.BYTES)
+
+      case d: DecimalType =>
+        HoodieSchema.createDecimal(d.precision, d.scale)
+
+      // Complex types
+      case ArrayType(elementType, containsNull) =>
+        val elementSchema = toHoodieType(elementType, containsNull, 
recordName, nameSpace)
+        HoodieSchema.createArray(elementSchema)
+
+      case MapType(StringType, valueType, valueContainsNull) =>
+        val valueSchema = toHoodieType(valueType, valueContainsNull, 
recordName, nameSpace)
+        HoodieSchema.createMap(valueSchema)
+
+      case st: StructType =>
+        val childNameSpace = if (nameSpace != "") s"$nameSpace.$recordName" 
else recordName
+
+        // Check if this might be a union (using heuristic like Avro converter)
+        if (canBeUnion(st)) {
+          val nonNullUnionFieldTypes = st.map { f =>
+            toHoodieType(f.dataType, nullable = false, f.name, childNameSpace)
+          }
+          val unionFieldTypes = if (nullable) {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            types.add(HoodieSchema.create(HoodieSchemaType.NULL))
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          } else {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          }
+          HoodieSchema.createUnion(unionFieldTypes)
+        } else {
+          // Create record
+          val fields = st.map { f =>
+            val fieldSchema = toHoodieType(f.dataType, f.nullable, f.name, 
childNameSpace)
+            val doc = if (f.metadata.contains("comment")) 
f.metadata.getString("comment") else null

Review Comment:
   ```suggestion
               val doc = f.getComment.orNull
   ```



##########
hudi-spark-datasource/hudi-spark-common/src/main/scala/org/apache/spark/sql/avro/HoodieSchemaInternalConverters.scala:
##########
@@ -0,0 +1,236 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.avro
+
+import org.apache.hudi.HoodieSchemaConverters
+import org.apache.hudi.common.schema.{HoodieSchema, HoodieSchemaField, 
HoodieSchemaType}
+
+import org.apache.spark.annotation.DeveloperApi
+import org.apache.spark.sql.types._
+
+import scala.collection.JavaConverters._
+
+/**
+ * This object contains methods that are used to convert HoodieSchema to Spark 
SQL schemas and vice versa.
+ *
+ * NOTE: This provides direct conversion between HoodieSchema and Spark 
DataType
+ * without going through Avro Schema intermediary.
+ */
+
+@DeveloperApi
+private[sql] object HoodieSchemaInternalConverters extends 
HoodieSchemaConverters {
+
+  /**
+   * Internal wrapper for SQL data type and nullability.
+   */
+  case class SchemaType(dataType: DataType, nullable: Boolean)
+
+  override def toSqlType(hoodieSchema: HoodieSchema): (DataType, Boolean) = {
+    val result = toSqlTypeHelper(hoodieSchema, Set.empty)
+    (result.dataType, result.nullable)
+  }
+
+  override def toHoodieType(catalystType: DataType, nullable: Boolean, 
recordName: String, nameSpace: String): HoodieSchema = {
+    val schema = catalystType match {
+      // Primitive types
+      case BooleanType => HoodieSchema.create(HoodieSchemaType.BOOLEAN)
+      case ByteType | ShortType | IntegerType => 
HoodieSchema.create(HoodieSchemaType.INT)
+      case LongType => HoodieSchema.create(HoodieSchemaType.LONG)
+      case DateType => HoodieSchema.createDate()
+      case TimestampType => HoodieSchema.createTimestampMicros()
+      case TimestampNTZType => HoodieSchema.createLocalTimestampMicros()
+      case FloatType => HoodieSchema.create(HoodieSchemaType.FLOAT)
+      case DoubleType => HoodieSchema.create(HoodieSchemaType.DOUBLE)
+      case StringType | _: CharType | _: VarcharType => 
HoodieSchema.create(HoodieSchemaType.STRING)
+      case NullType => HoodieSchema.create(HoodieSchemaType.NULL)
+      case BinaryType => HoodieSchema.create(HoodieSchemaType.BYTES)
+
+      case d: DecimalType =>
+        HoodieSchema.createDecimal(d.precision, d.scale)
+
+      // Complex types
+      case ArrayType(elementType, containsNull) =>
+        val elementSchema = toHoodieType(elementType, containsNull, 
recordName, nameSpace)
+        HoodieSchema.createArray(elementSchema)
+
+      case MapType(StringType, valueType, valueContainsNull) =>
+        val valueSchema = toHoodieType(valueType, valueContainsNull, 
recordName, nameSpace)
+        HoodieSchema.createMap(valueSchema)
+
+      case st: StructType =>
+        val childNameSpace = if (nameSpace != "") s"$nameSpace.$recordName" 
else recordName
+
+        // Check if this might be a union (using heuristic like Avro converter)
+        if (canBeUnion(st)) {
+          val nonNullUnionFieldTypes = st.map { f =>
+            toHoodieType(f.dataType, nullable = false, f.name, childNameSpace)
+          }
+          val unionFieldTypes = if (nullable) {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            types.add(HoodieSchema.create(HoodieSchemaType.NULL))
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          } else {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          }
+          HoodieSchema.createUnion(unionFieldTypes)
+        } else {
+          // Create record
+          val fields = st.map { f =>
+            val fieldSchema = toHoodieType(f.dataType, f.nullable, f.name, 
childNameSpace)
+            val doc = if (f.metadata.contains("comment")) 
f.metadata.getString("comment") else null
+            HoodieSchemaField.of(f.name, fieldSchema, doc)
+          }
+
+          val fieldsJava = new java.util.ArrayList[HoodieSchemaField]()
+          fields.foreach(fieldsJava.add)
+
+          HoodieSchema.createRecord(recordName, nameSpace, null, fieldsJava)
+        }
+
+      case other => throw new IncompatibleSchemaException(s"Unexpected Spark 
DataType: $other")
+    }
+
+    // Wrap with null union if nullable (and not already a union)
+    if (nullable && catalystType != NullType && schema.getType != 
HoodieSchemaType.UNION) {
+      HoodieSchema.createNullable(schema)
+    } else {
+      schema
+    }
+  }
+
+  private def toSqlTypeHelper(hoodieSchema: HoodieSchema, existingRecordNames: 
Set[String]): SchemaType = {
+    hoodieSchema.getType match {
+      // Primitive types
+      case HoodieSchemaType.INT => SchemaType(IntegerType, nullable = false)
+      case HoodieSchemaType.STRING => SchemaType(StringType, nullable = false)
+      case HoodieSchemaType.BOOLEAN => SchemaType(BooleanType, nullable = 
false)
+      case HoodieSchemaType.BYTES => SchemaType(BinaryType, nullable = false)
+      case HoodieSchemaType.DOUBLE => SchemaType(DoubleType, nullable = false)
+      case HoodieSchemaType.FLOAT => SchemaType(FloatType, nullable = false)
+      case HoodieSchemaType.LONG => SchemaType(LongType, nullable = false)
+      case HoodieSchemaType.NULL => SchemaType(NullType, nullable = true)
+      case HoodieSchemaType.ENUM => SchemaType(StringType, nullable = false)
+
+      // Logical types
+      case HoodieSchemaType.DATE =>
+        SchemaType(DateType, nullable = false)
+
+      case HoodieSchemaType.TIMESTAMP =>
+        hoodieSchema match {
+          case ts: HoodieSchema.Timestamp =>
+            if (ts.isUtcAdjusted) {
+              SchemaType(TimestampType, nullable = false)
+            } else {
+              SchemaType(TimestampNTZType, nullable = false)
+            }
+          case _ =>
+            // Fallback for non-specialized timestamp schema
+            SchemaType(TimestampType, nullable = false)

Review Comment:
   One cool feature of scala is that you can add another condition in the 
matching so you could rewrite this as:
   
   ```
     case ts: HoodieSchema.Timestamp if !ts.isUtcAdjusted =>
               SchemaType(TimestampNTZType, nullable = false)
     case _ =>
               SchemaType(TimestampType, nullable = false)
   ```



##########
hudi-spark-datasource/hudi-spark-common/src/main/scala/org/apache/spark/sql/avro/HoodieSchemaInternalConverters.scala:
##########
@@ -0,0 +1,236 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.avro
+
+import org.apache.hudi.HoodieSchemaConverters
+import org.apache.hudi.common.schema.{HoodieSchema, HoodieSchemaField, 
HoodieSchemaType}
+
+import org.apache.spark.annotation.DeveloperApi
+import org.apache.spark.sql.types._
+
+import scala.collection.JavaConverters._
+
+/**
+ * This object contains methods that are used to convert HoodieSchema to Spark 
SQL schemas and vice versa.
+ *
+ * NOTE: This provides direct conversion between HoodieSchema and Spark 
DataType
+ * without going through Avro Schema intermediary.
+ */
+
+@DeveloperApi
+private[sql] object HoodieSchemaInternalConverters extends 
HoodieSchemaConverters {
+
+  /**
+   * Internal wrapper for SQL data type and nullability.
+   */
+  case class SchemaType(dataType: DataType, nullable: Boolean)
+
+  override def toSqlType(hoodieSchema: HoodieSchema): (DataType, Boolean) = {
+    val result = toSqlTypeHelper(hoodieSchema, Set.empty)
+    (result.dataType, result.nullable)
+  }
+
+  override def toHoodieType(catalystType: DataType, nullable: Boolean, 
recordName: String, nameSpace: String): HoodieSchema = {
+    val schema = catalystType match {
+      // Primitive types
+      case BooleanType => HoodieSchema.create(HoodieSchemaType.BOOLEAN)
+      case ByteType | ShortType | IntegerType => 
HoodieSchema.create(HoodieSchemaType.INT)
+      case LongType => HoodieSchema.create(HoodieSchemaType.LONG)
+      case DateType => HoodieSchema.createDate()
+      case TimestampType => HoodieSchema.createTimestampMicros()
+      case TimestampNTZType => HoodieSchema.createLocalTimestampMicros()
+      case FloatType => HoodieSchema.create(HoodieSchemaType.FLOAT)
+      case DoubleType => HoodieSchema.create(HoodieSchemaType.DOUBLE)
+      case StringType | _: CharType | _: VarcharType => 
HoodieSchema.create(HoodieSchemaType.STRING)
+      case NullType => HoodieSchema.create(HoodieSchemaType.NULL)
+      case BinaryType => HoodieSchema.create(HoodieSchemaType.BYTES)
+
+      case d: DecimalType =>
+        HoodieSchema.createDecimal(d.precision, d.scale)

Review Comment:
   In the existing struct type to avro, it looks like a fixed size is used 
instead



##########
hudi-spark-datasource/hudi-spark-common/src/main/scala/org/apache/spark/sql/avro/HoodieSchemaInternalConverters.scala:
##########
@@ -0,0 +1,236 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.avro
+
+import org.apache.hudi.HoodieSchemaConverters
+import org.apache.hudi.common.schema.{HoodieSchema, HoodieSchemaField, 
HoodieSchemaType}
+
+import org.apache.spark.annotation.DeveloperApi
+import org.apache.spark.sql.types._
+
+import scala.collection.JavaConverters._
+
+/**
+ * This object contains methods that are used to convert HoodieSchema to Spark 
SQL schemas and vice versa.
+ *
+ * NOTE: This provides direct conversion between HoodieSchema and Spark 
DataType
+ * without going through Avro Schema intermediary.
+ */
+
+@DeveloperApi
+private[sql] object HoodieSchemaInternalConverters extends 
HoodieSchemaConverters {

Review Comment:
   The naming is very similar to `InternalSchemaConverter` which confused me at 
first. 



##########
hudi-spark-datasource/hudi-spark-common/src/main/scala/org/apache/spark/sql/avro/HoodieSchemaInternalConverters.scala:
##########
@@ -0,0 +1,236 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.avro
+
+import org.apache.hudi.HoodieSchemaConverters
+import org.apache.hudi.common.schema.{HoodieSchema, HoodieSchemaField, 
HoodieSchemaType}
+
+import org.apache.spark.annotation.DeveloperApi
+import org.apache.spark.sql.types._
+
+import scala.collection.JavaConverters._
+
+/**
+ * This object contains methods that are used to convert HoodieSchema to Spark 
SQL schemas and vice versa.
+ *
+ * NOTE: This provides direct conversion between HoodieSchema and Spark 
DataType
+ * without going through Avro Schema intermediary.
+ */
+
+@DeveloperApi
+private[sql] object HoodieSchemaInternalConverters extends 
HoodieSchemaConverters {
+
+  /**
+   * Internal wrapper for SQL data type and nullability.
+   */
+  case class SchemaType(dataType: DataType, nullable: Boolean)
+
+  override def toSqlType(hoodieSchema: HoodieSchema): (DataType, Boolean) = {
+    val result = toSqlTypeHelper(hoodieSchema, Set.empty)
+    (result.dataType, result.nullable)
+  }
+
+  override def toHoodieType(catalystType: DataType, nullable: Boolean, 
recordName: String, nameSpace: String): HoodieSchema = {
+    val schema = catalystType match {
+      // Primitive types
+      case BooleanType => HoodieSchema.create(HoodieSchemaType.BOOLEAN)
+      case ByteType | ShortType | IntegerType => 
HoodieSchema.create(HoodieSchemaType.INT)
+      case LongType => HoodieSchema.create(HoodieSchemaType.LONG)
+      case DateType => HoodieSchema.createDate()
+      case TimestampType => HoodieSchema.createTimestampMicros()
+      case TimestampNTZType => HoodieSchema.createLocalTimestampMicros()
+      case FloatType => HoodieSchema.create(HoodieSchemaType.FLOAT)
+      case DoubleType => HoodieSchema.create(HoodieSchemaType.DOUBLE)
+      case StringType | _: CharType | _: VarcharType => 
HoodieSchema.create(HoodieSchemaType.STRING)
+      case NullType => HoodieSchema.create(HoodieSchemaType.NULL)
+      case BinaryType => HoodieSchema.create(HoodieSchemaType.BYTES)
+
+      case d: DecimalType =>
+        HoodieSchema.createDecimal(d.precision, d.scale)
+
+      // Complex types
+      case ArrayType(elementType, containsNull) =>
+        val elementSchema = toHoodieType(elementType, containsNull, 
recordName, nameSpace)
+        HoodieSchema.createArray(elementSchema)
+
+      case MapType(StringType, valueType, valueContainsNull) =>
+        val valueSchema = toHoodieType(valueType, valueContainsNull, 
recordName, nameSpace)
+        HoodieSchema.createMap(valueSchema)
+
+      case st: StructType =>
+        val childNameSpace = if (nameSpace != "") s"$nameSpace.$recordName" 
else recordName
+
+        // Check if this might be a union (using heuristic like Avro converter)
+        if (canBeUnion(st)) {
+          val nonNullUnionFieldTypes = st.map { f =>
+            toHoodieType(f.dataType, nullable = false, f.name, childNameSpace)
+          }
+          val unionFieldTypes = if (nullable) {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            types.add(HoodieSchema.create(HoodieSchemaType.NULL))
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          } else {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          }
+          HoodieSchema.createUnion(unionFieldTypes)
+        } else {
+          // Create record
+          val fields = st.map { f =>
+            val fieldSchema = toHoodieType(f.dataType, f.nullable, f.name, 
childNameSpace)
+            val doc = if (f.metadata.contains("comment")) 
f.metadata.getString("comment") else null
+            HoodieSchemaField.of(f.name, fieldSchema, doc)
+          }
+
+          val fieldsJava = new java.util.ArrayList[HoodieSchemaField]()
+          fields.foreach(fieldsJava.add)
+
+          HoodieSchema.createRecord(recordName, nameSpace, null, fieldsJava)
+        }
+
+      case other => throw new IncompatibleSchemaException(s"Unexpected Spark 
DataType: $other")
+    }
+
+    // Wrap with null union if nullable (and not already a union)
+    if (nullable && catalystType != NullType && schema.getType != 
HoodieSchemaType.UNION) {
+      HoodieSchema.createNullable(schema)
+    } else {
+      schema
+    }
+  }
+
+  private def toSqlTypeHelper(hoodieSchema: HoodieSchema, existingRecordNames: 
Set[String]): SchemaType = {
+    hoodieSchema.getType match {
+      // Primitive types
+      case HoodieSchemaType.INT => SchemaType(IntegerType, nullable = false)
+      case HoodieSchemaType.STRING => SchemaType(StringType, nullable = false)
+      case HoodieSchemaType.BOOLEAN => SchemaType(BooleanType, nullable = 
false)
+      case HoodieSchemaType.BYTES => SchemaType(BinaryType, nullable = false)
+      case HoodieSchemaType.DOUBLE => SchemaType(DoubleType, nullable = false)
+      case HoodieSchemaType.FLOAT => SchemaType(FloatType, nullable = false)
+      case HoodieSchemaType.LONG => SchemaType(LongType, nullable = false)
+      case HoodieSchemaType.NULL => SchemaType(NullType, nullable = true)
+      case HoodieSchemaType.ENUM => SchemaType(StringType, nullable = false)
+
+      // Logical types
+      case HoodieSchemaType.DATE =>
+        SchemaType(DateType, nullable = false)
+
+      case HoodieSchemaType.TIMESTAMP =>
+        hoodieSchema match {
+          case ts: HoodieSchema.Timestamp =>
+            if (ts.isUtcAdjusted) {
+              SchemaType(TimestampType, nullable = false)
+            } else {
+              SchemaType(TimestampNTZType, nullable = false)
+            }
+          case _ =>
+            // Fallback for non-specialized timestamp schema
+            SchemaType(TimestampType, nullable = false)
+        }
+
+      case HoodieSchemaType.DECIMAL =>
+        hoodieSchema match {
+          case dec: HoodieSchema.Decimal =>
+            SchemaType(DecimalType(dec.getPrecision, dec.getScale), nullable = 
false)
+          case _ =>
+            throw new IncompatibleSchemaException(
+              s"DECIMAL type must be HoodieSchema.Decimal instance, got: 
${hoodieSchema.getClass}")
+        }
+
+      case HoodieSchemaType.FIXED =>
+        // FIXED can be either binary or decimal with logical type
+        hoodieSchema match {
+          case dec: HoodieSchema.Decimal =>
+            SchemaType(DecimalType(dec.getPrecision, dec.getScale), nullable = 
false)
+          case _ =>
+            SchemaType(BinaryType, nullable = false)
+        }
+
+      // Complex types
+      case HoodieSchemaType.RECORD =>
+        val fullName = hoodieSchema.getFullName
+        if (existingRecordNames.contains(fullName)) {
+          throw new IncompatibleSchemaException(
+            s"""
+               |Found recursive reference in HoodieSchema, which cannot be 
processed by Spark:
+               |$fullName
+             """.stripMargin)
+        }
+        val newRecordNames = existingRecordNames + fullName
+        val fields = hoodieSchema.getFields.asScala.map { f =>
+          val schemaType = toSqlTypeHelper(f.schema(), newRecordNames)
+          StructField(f.name(), schemaType.dataType, schemaType.nullable)

Review Comment:
   In one other converter I've seen, we carry through the doc as a comment in 
the metadata. Let's do that here as well in case users are leveraging that.



##########
hudi-spark-datasource/hudi-spark-common/src/main/scala/org/apache/spark/sql/avro/HoodieSchemaInternalConverters.scala:
##########
@@ -0,0 +1,236 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.avro
+
+import org.apache.hudi.HoodieSchemaConverters
+import org.apache.hudi.common.schema.{HoodieSchema, HoodieSchemaField, 
HoodieSchemaType}
+
+import org.apache.spark.annotation.DeveloperApi
+import org.apache.spark.sql.types._
+
+import scala.collection.JavaConverters._
+
+/**
+ * This object contains methods that are used to convert HoodieSchema to Spark 
SQL schemas and vice versa.
+ *
+ * NOTE: This provides direct conversion between HoodieSchema and Spark 
DataType
+ * without going through Avro Schema intermediary.
+ */
+
+@DeveloperApi
+private[sql] object HoodieSchemaInternalConverters extends 
HoodieSchemaConverters {
+
+  /**
+   * Internal wrapper for SQL data type and nullability.
+   */
+  case class SchemaType(dataType: DataType, nullable: Boolean)
+
+  override def toSqlType(hoodieSchema: HoodieSchema): (DataType, Boolean) = {
+    val result = toSqlTypeHelper(hoodieSchema, Set.empty)
+    (result.dataType, result.nullable)
+  }
+
+  override def toHoodieType(catalystType: DataType, nullable: Boolean, 
recordName: String, nameSpace: String): HoodieSchema = {
+    val schema = catalystType match {
+      // Primitive types
+      case BooleanType => HoodieSchema.create(HoodieSchemaType.BOOLEAN)
+      case ByteType | ShortType | IntegerType => 
HoodieSchema.create(HoodieSchemaType.INT)
+      case LongType => HoodieSchema.create(HoodieSchemaType.LONG)
+      case DateType => HoodieSchema.createDate()
+      case TimestampType => HoodieSchema.createTimestampMicros()
+      case TimestampNTZType => HoodieSchema.createLocalTimestampMicros()
+      case FloatType => HoodieSchema.create(HoodieSchemaType.FLOAT)
+      case DoubleType => HoodieSchema.create(HoodieSchemaType.DOUBLE)
+      case StringType | _: CharType | _: VarcharType => 
HoodieSchema.create(HoodieSchemaType.STRING)
+      case NullType => HoodieSchema.create(HoodieSchemaType.NULL)
+      case BinaryType => HoodieSchema.create(HoodieSchemaType.BYTES)
+
+      case d: DecimalType =>
+        HoodieSchema.createDecimal(d.precision, d.scale)
+
+      // Complex types
+      case ArrayType(elementType, containsNull) =>
+        val elementSchema = toHoodieType(elementType, containsNull, 
recordName, nameSpace)
+        HoodieSchema.createArray(elementSchema)
+
+      case MapType(StringType, valueType, valueContainsNull) =>
+        val valueSchema = toHoodieType(valueType, valueContainsNull, 
recordName, nameSpace)
+        HoodieSchema.createMap(valueSchema)
+
+      case st: StructType =>
+        val childNameSpace = if (nameSpace != "") s"$nameSpace.$recordName" 
else recordName
+
+        // Check if this might be a union (using heuristic like Avro converter)
+        if (canBeUnion(st)) {
+          val nonNullUnionFieldTypes = st.map { f =>
+            toHoodieType(f.dataType, nullable = false, f.name, childNameSpace)
+          }
+          val unionFieldTypes = if (nullable) {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            types.add(HoodieSchema.create(HoodieSchemaType.NULL))
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          } else {
+            val types = new java.util.ArrayList[HoodieSchema]()
+            nonNullUnionFieldTypes.foreach(types.add)
+            types
+          }
+          HoodieSchema.createUnion(unionFieldTypes)
+        } else {
+          // Create record
+          val fields = st.map { f =>
+            val fieldSchema = toHoodieType(f.dataType, f.nullable, f.name, 
childNameSpace)
+            val doc = if (f.metadata.contains("comment")) 
f.metadata.getString("comment") else null
+            HoodieSchemaField.of(f.name, fieldSchema, doc)
+          }
+
+          val fieldsJava = new java.util.ArrayList[HoodieSchemaField]()
+          fields.foreach(fieldsJava.add)
+
+          HoodieSchema.createRecord(recordName, nameSpace, null, fieldsJava)
+        }
+
+      case other => throw new IncompatibleSchemaException(s"Unexpected Spark 
DataType: $other")
+    }
+
+    // Wrap with null union if nullable (and not already a union)
+    if (nullable && catalystType != NullType && schema.getType != 
HoodieSchemaType.UNION) {
+      HoodieSchema.createNullable(schema)
+    } else {
+      schema
+    }
+  }
+
+  private def toSqlTypeHelper(hoodieSchema: HoodieSchema, existingRecordNames: 
Set[String]): SchemaType = {
+    hoodieSchema.getType match {
+      // Primitive types
+      case HoodieSchemaType.INT => SchemaType(IntegerType, nullable = false)
+      case HoodieSchemaType.STRING => SchemaType(StringType, nullable = false)
+      case HoodieSchemaType.BOOLEAN => SchemaType(BooleanType, nullable = 
false)
+      case HoodieSchemaType.BYTES => SchemaType(BinaryType, nullable = false)

Review Comment:
   Group `FIXED` with the `BYTES` here



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