szehon-ho commented on code in PR #7539:
URL: https://github.com/apache/iceberg/pull/7539#discussion_r1191925271


##########
core/src/main/java/org/apache/iceberg/BaseEntriesTable.java:
##########
@@ -125,31 +130,120 @@ ManifestFile manifest() {
 
     @Override
     public CloseableIterable<StructLike> rows() {
-      // Project data-file fields
-      CloseableIterable<StructLike> prunedRows;
-      if (manifest.content() == ManifestContent.DATA) {
-        prunedRows =
+      Types.NestedField readableMetricsField = 
projection.findField(MetricsUtil.READABLE_METRICS);
+
+      if (readableMetricsField == null) {
+        CloseableIterable<StructLike> entryAsStruct =
             CloseableIterable.transform(
-                ManifestFiles.read(manifest, io).project(fileSchema).entries(),
-                file -> (GenericManifestEntry<DataFile>) file);
+                entries(fileProjection),
+                entry -> (GenericManifestEntry<? extends ContentFile<?>>) 
entry);
+
+        StructProjection structProjection = projectNonReadable(projection);
+        return CloseableIterable.transform(entryAsStruct, 
structProjection::wrap);
       } else {
-        prunedRows =
-            CloseableIterable.transform(
-                ManifestFiles.readDeleteManifest(manifest, io, specsById)
-                    .project(fileSchema)
-                    .entries(),
-                file -> (GenericManifestEntry<DeleteFile>) file);
+        Schema requiredFileProjection = requiredFileProjection();
+        Schema actualProjection = removeReadableMetrics(readableMetricsField);
+        StructProjection structProjection = 
projectNonReadable(actualProjection);
+
+        return CloseableIterable.transform(
+            entries(requiredFileProjection),
+            entry -> withReadableMetrics(structProjection, entry, 
readableMetricsField));
       }
+    }
+
+    /**
+     * Remove virtual columns from the file projection and ensure that the 
underlying metrics used
+     * to create those columns are part of the file projection
+     *
+     * @return file projection with required columns to read readable metrics
+     */
+    private Schema requiredFileProjection() {
+      Schema projectionForReadableMetrics =
+          new Schema(
+              MetricsUtil.READABLE_METRIC_COLS.stream()
+                  .map(MetricsUtil.ReadableMetricColDefinition::originalCol)
+                  .collect(Collectors.toList()));
+      return TypeUtil.join(fileProjection, projectionForReadableMetrics);
+    }
 
-      // Project non-readable fields
-      Schema readSchema = ManifestEntry.wrapFileSchema(fileSchema.asStruct());
-      StructProjection projection = StructProjection.create(readSchema, 
schema);
-      return CloseableIterable.transform(prunedRows, projection::wrap);
+    private Schema removeReadableMetrics(Types.NestedField 
readableMetricsField) {
+      Set<Integer> readableMetricsIds = 
TypeUtil.getProjectedIds(readableMetricsField.type());
+      return TypeUtil.selectNot(projection, readableMetricsIds);
+    }
+
+    private StructProjection projectNonReadable(Schema projectedSchema) {

Review Comment:
   Quesiton, while we make one more change, what do you think of renaming this 
method to structProjection()?  Realize it's from the original comment but Im 
not 100% sure what that was referring to.  Looks like it is just a standard 
projection of ManifestEntry to me?  I may be missing something though



##########
core/src/main/java/org/apache/iceberg/BaseEntriesTable.java:
##########
@@ -125,31 +130,120 @@ ManifestFile manifest() {
 
     @Override
     public CloseableIterable<StructLike> rows() {
-      // Project data-file fields
-      CloseableIterable<StructLike> prunedRows;
-      if (manifest.content() == ManifestContent.DATA) {
-        prunedRows =
+      Types.NestedField readableMetricsField = 
projection.findField(MetricsUtil.READABLE_METRICS);
+
+      if (readableMetricsField == null) {
+        CloseableIterable<StructLike> entryAsStruct =
             CloseableIterable.transform(
-                ManifestFiles.read(manifest, io).project(fileSchema).entries(),
-                file -> (GenericManifestEntry<DataFile>) file);
+                entries(fileProjection),
+                entry -> (GenericManifestEntry<? extends ContentFile<?>>) 
entry);
+
+        StructProjection structProjection = projectNonReadable(projection);
+        return CloseableIterable.transform(entryAsStruct, 
structProjection::wrap);
       } else {
-        prunedRows =
-            CloseableIterable.transform(
-                ManifestFiles.readDeleteManifest(manifest, io, specsById)
-                    .project(fileSchema)
-                    .entries(),
-                file -> (GenericManifestEntry<DeleteFile>) file);
+        Schema requiredFileProjection = requiredFileProjection();
+        Schema actualProjection = removeReadableMetrics(readableMetricsField);
+        StructProjection structProjection = 
projectNonReadable(actualProjection);
+
+        return CloseableIterable.transform(
+            entries(requiredFileProjection),
+            entry -> withReadableMetrics(structProjection, entry, 
readableMetricsField));
       }
+    }
+
+    /**
+     * Remove virtual columns from the file projection and ensure that the 
underlying metrics used
+     * to create those columns are part of the file projection
+     *
+     * @return file projection with required columns to read readable metrics
+     */
+    private Schema requiredFileProjection() {
+      Schema projectionForReadableMetrics =
+          new Schema(
+              MetricsUtil.READABLE_METRIC_COLS.stream()
+                  .map(MetricsUtil.ReadableMetricColDefinition::originalCol)
+                  .collect(Collectors.toList()));
+      return TypeUtil.join(fileProjection, projectionForReadableMetrics);
+    }
 
-      // Project non-readable fields
-      Schema readSchema = ManifestEntry.wrapFileSchema(fileSchema.asStruct());
-      StructProjection projection = StructProjection.create(readSchema, 
schema);
-      return CloseableIterable.transform(prunedRows, projection::wrap);
+    private Schema removeReadableMetrics(Types.NestedField 
readableMetricsField) {
+      Set<Integer> readableMetricsIds = 
TypeUtil.getProjectedIds(readableMetricsField.type());
+      return TypeUtil.selectNot(projection, readableMetricsIds);
+    }
+
+    private StructProjection projectNonReadable(Schema projectedSchema) {

Review Comment:
   Quesiton, while we make one more change, what do you think of renaming this 
method to structProjection()?  Realize it's from the original comment but Im 
not 100% sure what that was referring to, what is non-readable?  Looks like it 
is just a standard projection of ManifestEntry to me?  I may be missing 
something though



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