small generalization

extensions/parquet/table/src/main/java/io/deephaven/parquet/table/location/ParquetColumnResolver.java

@@ -6,13 +6,12 @@
 import io.deephaven.engine.table.impl.locations.TableKey;
 import io.deephaven.parquet.table.ParquetInstructions;
 import org.apache.parquet.column.ColumnDescriptor;
+import org.apache.parquet.schema.MessageType;
 
 import java.util.Optional;
 
 /**
- * A mapping between Deephaven column names and Parquet {@link ColumnDescriptor column descriptors}.
- *
- * TODO: describe better
+ * A resolver from Deephaven column names to Parquet paths.
  */
 public interface ParquetColumnResolver {
 
@@ -24,12 +23,22 @@ interface Factory {
         /**
          * TODO: description
          *
+         *
+         *
          * @param tableKey the table key
          * @param tableLocationKey the Parquet TLK
          * @return the Parquet column resolver
          */
         ParquetColumnResolver of(TableKey tableKey, ParquetTableLocationKey tableLocationKey);
     }
 
-    Optional<ColumnDescriptor> of(String columnName);
+    /**
+     *
+     *
+     * @param columnName the column name
+     * @return the path to the leaf field in the schema
+     * @see ColumnDescriptor#getPath()
+     * @see MessageType#getColumnDescription(String[])
+     */
+    Optional<String[]> of(String columnName);
 }

extensions/parquet/table/src/main/java/io/deephaven/parquet/table/location/ParquetColumnResolverMap.java

@@ -29,14 +29,14 @@ public static Builder builder() {
     public abstract MessageType schema();
 
     /**
-     * The map from Deephaven column name to {@link ColumnDescriptor}. The {@link #schema()} must contains the column
-     * descriptors.
+     * The map from Deephaven column name to {@link ColumnDescriptor}. The {@link #schema()} must contain each column
+     * descriptor.
      */
     public abstract Map<String, ColumnDescriptor> mapping();
 
     @Override
-    public final Optional<ColumnDescriptor> of(String columnName) {
-        return Optional.ofNullable(mapping().get(columnName));
+    public final Optional<String[]> of(String columnName) {
+        return Optional.ofNullable(mapping().get(columnName)).map(ColumnDescriptor::getPath);
     }
 
     public interface Builder {

extensions/parquet/table/src/main/java/io/deephaven/parquet/table/location/ParquetTableLocation.java

@@ -193,7 +193,6 @@ protected ColumnLocation makeColumnLocation(@NotNull final String columnName) {
         } else {
             // empty list will result in exists=false
             nameList = resolver.of(columnName)
-                    .map(ColumnDescriptor::getPath)
                     .map(Arrays::asList)
                     .orElse(List.of());
         }

extensions/parquet/table/src/test/java/io/deephaven/parquet/table/location/ParquetFieldIdColumnResolverFactoryTest.java

@@ -144,7 +144,6 @@ public void ambiguousFields() {
 
     @Test
     public void ambiguousFieldsNested() {
-        final ParquetFieldIdColumnResolverFactory factory = ParquetFieldIdColumnResolverFactory.of(Map.of("Col1", 1));
         // X (1), list, element (2)
         // Y (2), list, element (1)
         // Z (3)
@@ -158,7 +157,7 @@ public void ambiguousFieldsNested() {
         // for example, an implementation could choose to consider the innermost (or outermost) field id for matching
         // purposes.
         try {
-            factory.of(schema);
+            ParquetFieldIdColumnResolverFactory.of(Map.of("Col1", 1)).of(schema);
             failBecauseExceptionWasNotThrown(IllegalArgumentException.class);
         } catch (IllegalArgumentException e) {
             assertThat(e).hasMessageContaining("Col1 -> 1 has multiple paths [X, list, element], [Y, list, element]");