#1737 - PersistenceException while using aggregate query on related entity

This part includes support for joins off an aggregation formula
on a ManyToOne.

e.g. We use min(customer) ... to 'query join' to customer
in the query below.

    List<Contact> contacts = Ebean.find(Contact.class)
      .select("lastName, min(customer)")
      .fetchQuery("customer", "name, status")
      .findList();

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

@@ -29,6 +29,8 @@ public class SqlTreeProperties {
 
   private boolean allProperties;
 
+  private boolean aggregationManyToOne;
+
   private boolean aggregation;
 
   private String aggregationPath;
@@ -47,6 +49,15 @@ public class SqlTreeProperties {
   public void add(STreeProperty prop) {
     propsList.add(prop);
     propNames.add(prop.getName());
+    if (prop.isAggregation()) {
+      if (!aggregation) {
+        aggregation = true;
+        aggregationPath = prop.getElPrefix();
+      }
+      if (prop.isAggregationManyToOne()) {
+        aggregationManyToOne = true;
+      }
+    }
   }
 
   public STreeProperty[] getProps() {
@@ -85,6 +96,13 @@ public class SqlTreeProperties {
     }
   }
 
+  /**
+   * Return true if this is an aggregation formula on a ManyToOne.
+   */
+  boolean isAggregationManyToOne() {
+    return aggregationManyToOne;
+  }
+
   /**
    * Return true if this contains an aggregation property.
    */
@@ -92,33 +110,17 @@ public class SqlTreeProperties {
     return aggregation;
   }
 
-  /**
-   * Check for aggregation (need for groug by clause).
-   */
-  public void checkAggregation() {
-    aggregationJoin();
-  }
-
   /**
    * Return the property to join for aggregation.
    */
   private String aggregationJoin() {
-    if (!allProperties) {
-      for (STreeProperty beanProperty : propsList) {
-        if (beanProperty.isAggregation()) {
-          aggregation = true;
-          aggregationPath = beanProperty.getElPrefix();
-          return aggregationPath;
-        }
-      }
-    }
-    return null;
+    return aggregationPath;
   }
 
   /**
    * Return true if a top level aggregation which means the Id property must be excluded.
    */
-  public boolean isAggregationRoot() {
+  boolean isAggregationRoot() {
     return aggregation && (aggregationPath == null);
   }
 }