#980 - fix several bugs in findSingleAttibute - Refactor moving logic into DefaultOrmQuery setDefaultSelectClause() from findSingleAttributeList() (to support alternate calling via EbeanServer)

src/main/java/io/ebeaninternal/server/query/SqlTreeBuilder.java

@@ -30,7 +30,7 @@ import java.util.Set;
 /**
  * Factory for SqlTree.
  */
-public class SqlTreeBuilder {
+public final class SqlTreeBuilder {
 
   private static final Logger logger = LoggerFactory.getLogger(SqlTreeBuilder.class);
 
@@ -323,7 +323,7 @@ public class SqlTreeBuilder {
 
     } else {
       // do not read Id on child beans (e.g. when used with fetch())
-      boolean withId = (query == null || !query.isSingleAttribute()); 
+      boolean withId = isNotSingleAttribute();
       return new SqlTreeNodeBean(prefix, prop, props, myList, withId, temporalMode, disableLazyLoad);
     }
   }
@@ -440,7 +440,7 @@ public class SqlTreeBuilder {
         p = desc.findBeanProperty("id");
         selectProps.add(p);
 
-      } else if (p.isId() && (query == null || !query.isSingleAttribute())) {
+      } else if (p.isId() && isNotSingleAttribute()) {
         // do not bother to include id for normal queries as the
         // id is always added (except for subQueries)
 
@@ -716,4 +716,11 @@ public class SqlTreeBuilder {
     }
 
   }
+
+  /**
+   * Return true if the query is not a single attribute query.
+   */
+  private boolean isNotSingleAttribute() {
+    return query == null || !query.isSingleAttribute();
+  }
 }

src/main/java/io/ebeaninternal/server/querydefn/DefaultOrmQuery.java

@@ -513,7 +513,12 @@ public class DefaultOrmQuery<T> implements SpiQuery<T> {
 
   @Override
   public void setDefaultSelectClause() {
-    detail.setDefaultSelectClause(beanDescriptor);
+    if (type != Type.ATTRIBUTE) {
+      detail.setDefaultSelectClause(beanDescriptor);
+    } else if (!detail.hasSelectClause()) {
+      // explicit empty select when single attribute query on non-root fetch path
+      detail.setEmptyBase();
+    }
   }
 
   @Override
@@ -1221,10 +1226,6 @@ public class DefaultOrmQuery<T> implements SpiQuery<T> {
   @Override
   @SuppressWarnings("unchecked")
   public <A> List<A> findSingleAttributeList() {
-    if (!detail.hasSelectClause()) {
-      // (no explicit select set - clear all properties)
-      detail.setBase(new OrmQueryProperties(null, new LinkedHashSet<>()));
-    }
     return (List<A>) server.findSingleAttributeList(this, null);
   }
 

src/main/java/io/ebeaninternal/server/querydefn/OrmQueryDetail.java

@@ -174,6 +174,13 @@ public class OrmQueryDetail implements Serializable {
     return baseProps.isIncluded(property);
   }
 
+  /**
+   * Set the base query properties to be empty.
+   */
+  public void setEmptyBase() {
+    this.baseProps = new OrmQueryProperties(null, new LinkedHashSet<>());
+  }
+
   /**
    * Set the base / root query properties.
    */