Only apply enhancements once for CoordinateAxis variables

Fixes #1436. Not perfect, breaks encapsulation, but
maintains API.

Author: lesserwhirls

cdm/core/src/main/java/ucar/nc2/dataset/VariableDS.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998-2018 John Caron and University Corporation for Atmospheric Research/Unidata
+ * Copyright (c) 1998-2025 John Caron and University Corporation for Atmospheric Research/Unidata
  * See LICENSE for license information.
  */
 package ucar.nc2.dataset;
@@ -494,9 +494,28 @@ protected Array _read(Section section) throws IOException, InvalidRangeException
   // do not call directly
   @Override
   public Array reallyRead(Variable client, CancelTask cancelTask) throws IOException {
-    if (orgVar == null)
+    if (orgVar == null) {
+      // possible aggregation
+      if (this.proxyReader != null && this.proxyReader instanceof ucar.nc2.ncml.Aggregation) {
+        return this.proxyReader.reallyRead(client, cancelTask);
+      }
       return getMissingDataArray(shape);
+    }
 
+    if (client instanceof CoordinateAxis) {
+      // If orgVar is a VariableDS (orgVar of a CoordinateAxis using the non-builder
+      // API, for example), call reallyRead on it, otherwise, enhancements will get
+      // applied twice in a second _read() call triggered by calling read() on the
+      // VariableDS.
+      if (orgVar instanceof VariableDS && !orgVar.hasCachedData()) {
+        return orgVar.reallyRead(client, cancelTask);
+      }
+      // Some aggregations use a DatasetProxyReader for reading a coordinate axis
+      // variable, so check to see if that's what we have and, if so, use it.
+      if (ucar.nc2.ncml.Aggregation.instanceOfDatasetProxyReader(this.proxyReader)) {
+        return this.proxyReader.reallyRead(client, cancelTask);
+      }
+    }
     return orgVar.read();
   }
 
@@ -508,9 +527,28 @@ public Array reallyRead(Variable client, Section section, CancelTask cancelTask)
     if ((null == section) || section.computeSize() == getSize())
       return reallyRead(client, cancelTask);
 
-    if (orgVar == null)
-      return getMissingDataArray(section.getShape());
+    if (orgVar == null) {
+      // possible aggregation
+      if (this.proxyReader != null && this.proxyReader instanceof ucar.nc2.ncml.Aggregation) {
+        return this.proxyReader.reallyRead(client, section, cancelTask);
+      }
+      return getMissingDataArray(shape);
+    }
 
+    if (client instanceof CoordinateAxis) {
+      // If orgVar is a VariableDS (orgVar of a CoordinateAxis using the non-builder
+      // API, for example), call reallyRead on it, otherwise, enhancements will get
+      // applied twice in a second _read() call triggered by calling read() on the
+      // VariableDS.
+      if (orgVar instanceof VariableDS && !orgVar.hasCachedData()) {
+        return orgVar.reallyRead(client, section, cancelTask);
+      }
+      // Some aggregations use a DatasetProxyReader for reading a coordinate axis
+      // variable, so check to see if that's what we have and, if so, use it.
+      if (ucar.nc2.ncml.Aggregation.instanceOfDatasetProxyReader(this.proxyReader)) {
+        return this.proxyReader.reallyRead(client, section, cancelTask);
+      }
+    }
     return orgVar.read(section);
   }
 

cdm/core/src/main/java/ucar/nc2/ncml/Aggregation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998-2020 John Caron and University Corporation for Atmospheric Research/Unidata
+ * Copyright (c) 1998-2025 John Caron and University Corporation for Atmospheric Research/Unidata
  * See LICENSE.txt for license information.
  */
 package ucar.nc2.ncml;
@@ -777,6 +777,11 @@ protected void setDatasetAcquireProxy(DatasetProxyReader proxy, Group g) throws
     }
   }
 
+  public static boolean instanceOfDatasetProxyReader(Object obj) {
+    if (obj == null)
+      return false;
+    return obj instanceof DatasetProxyReader;
+  }
 
   protected class DatasetProxyReader implements ProxyReader {
     Dataset dataset;