Added ability to set alias for root table of sql query.

src/main/java/com/avaje/ebean/Query.java

@@ -1230,4 +1230,9 @@ public interface Query<T> extends Serializable {
    * Return true if this query has forUpdate set.
    */
   public boolean isForUpdate();
+  
+  /**
+   * Set root table alias.
+   */
+  public Query<T> alias(String alias);
 }

src/main/java/com/avaje/ebeaninternal/api/SpiQuery.java

@@ -611,4 +611,9 @@ public interface SpiQuery<T> extends Query<T> {
      * Return true if this query has been cancelled.
      */
     public boolean isCancelled();
+    
+    /**
+     * Return root table alias set by {@link #alias(String)} command.
+     */
+    public String getAlias();
 }

src/main/java/com/avaje/ebeaninternal/server/query/SqlTreeBuilder.java

@@ -104,7 +104,7 @@ public class SqlTreeBuilder {
     this.queryDetail = query.getDetail();
 
     this.predicates = predicates;
-    this.alias = new SqlTreeAlias(request.getBeanDescriptor().getBaseTableAlias());
+    this.alias = new SqlTreeAlias(request.getQuery().getAlias()==null?request.getBeanDescriptor().getBaseTableAlias():request.getQuery().getAlias());
     this.ctx = new DefaultDbSqlContext(alias, tableAliasPlaceHolder, columnAliasPrefix, !subQuery);
   }
 

src/main/java/com/avaje/ebeaninternal/server/querydefn/DefaultOrmQuery.java

@@ -190,6 +190,11 @@ public class DefaultOrmQuery<T> implements SpiQuery<T> {
   private boolean autoFetchTuned;
 
   private boolean logSecondaryQuery;
+  
+  /**
+   * Root table alias. For {@link Query#alias(String)} command.
+   */
+  private String rootTableAlias=null;
 
   /**
    * The node of the bean or collection that fired lazy loading. Not null if profiling is on and
@@ -680,6 +685,7 @@ public class DefaultOrmQuery<T> implements SpiQuery<T> {
     builder.add(id != null);
     builder.add(rawSql == null ? 0 : rawSql.queryHash());
     builder.add(includeTableJoin != null ? includeTableJoin.queryHash() : 0);
+    builder.add(rootTableAlias);
 
     if (detail != null) {
       detail.queryPlanHash(request, builder);
@@ -1284,6 +1290,17 @@ public class DefaultOrmQuery<T> implements SpiQuery<T> {
       this.cancelableQuery = cancelableQuery;
     }
   }
+  
+  @Override
+  public Query<T> alias(String alias) {
+	  this.rootTableAlias=alias;
+	  return this;
+  }
+  
+  @Override
+  public String getAlias() {
+    return rootTableAlias;
+  }
 
   public void cancel() {
     synchronized (this) {