SQLServerDialect: Added comments and refactored some varibles

hibernate-core/src/main/java/org/hibernate/dialect/SQLServerDialect.java

@@ -38,6 +38,7 @@ import org.hibernate.type.StandardBasicTypes;
  */
 public class SQLServerDialect extends AbstractTransactSQLDialect {
 	private static final String SELECT = "select";
+	private static final String FROM = "from";
     private static final String DISTINCT = "distinct";
     
     
@@ -79,10 +80,8 @@ public class SQLServerDialect extends AbstractTransactSQLDialect {
 	 * <pre>
 	 * WITH query AS (SELECT ROW_NUMBER() OVER (ORDER BY orderby) as __hibernate_row_nr__, original_query_without_orderby)
 	 * SELECT * FROM query WHERE __hibernate_row_nr__ BEETWIN offset AND offset + last
-	 * --ORDER BY __hibernate_row_nr__
 	 * </pre>
 	 *
-	 * I don't think that the last order by clause is mandatory
 	 *
 	 * @param querySqlString The SQL statement to base the limit query off of.
 	 * @param offset Offset of the first row to be returned by the query (zero-based)
@@ -108,43 +107,68 @@ public class SQLServerDialect extends AbstractTransactSQLDialect {
 			sb.delete( orderByIndex, orderByIndex + orderby.length() );
 		}
 
+		// HHH-5715 bug fix
 		replaceDistinctWithGroupBy( sb );
 		
-		insertRowNumberFunction(sb, orderby);
+		insertRowNumberFunction( sb, orderby );
 		
         //Wrap the query within a with statement:
-        sb.insert(0, "WITH query AS (").append(") SELECT * FROM query ");
-        sb.append("WHERE __hibernate_row_nr__ BETWEEN ").append(offset + 1).append(" AND ").append(limit);
+        sb.insert( 0, "WITH query AS (").append(") SELECT * FROM query " );
+        sb.append( "WHERE __hibernate_row_nr__ BETWEEN " ).append(offset + 1).append( " AND " ).append( limit );
 
         return sb.toString();
 	}
 	
-	protected static void replaceDistinctWithGroupBy(StringBuilder sb) {
-		int distinctIndex = sb.indexOf( DISTINCT );
+	/**
+	 * Utility method that checks if the given sql query is a select distinct one and if so replaces the distinct
+	 * select with an equivelant simple select with a group by clause. See {@link SQLServerDialectTestCase#testReplaceDistinctWithGroupBy()}
+	 * 
+	 * @param an sql query
+	 */
+	protected static void replaceDistinctWithGroupBy(StringBuilder sql) {
+		int distinctIndex = sql.indexOf( DISTINCT );
 		if (distinctIndex > 0) {
-			
-			sb.delete(distinctIndex, distinctIndex + DISTINCT.length() + 1);
-			sb.append(" group by").append(getSelectFieldsWithoutAs(sb));
+			sql.delete(distinctIndex, distinctIndex + DISTINCT.length() + 1);
+			sql.append(" group by").append(getSelectFieldsWithoutAs(sql));
 		}
 	}
 
+	/**
+	 * This utility method searches the given sql query for the fields of the select statement and
+	 * returns them without the as statement. See {@link SQLServerDialectTestCase#testGetSelectFieldsWithoutAs()}
+	 * 
+	 * @param an sql query
+	 * @return the fields of the select statement without their alias
+	 */
 	protected static CharSequence getSelectFieldsWithoutAs(StringBuilder sql) {
-		String select = sql.substring( sql.indexOf(SELECT) + SELECT.length(), sql.indexOf("from"));
+		String select = sql.substring( sql.indexOf(SELECT) + SELECT.length(), sql.indexOf(FROM));
 		
 		// Strip the as clauses
-		return stripAsStatement(select);
+		return stripAsStatement( select );
 	}
 
+	/**
+	 * Utility method that strips the as statements. See {@link SQLServerDialectTestCase#testStripAsStatement()}
+	 * 
+	 * @param a string to replace the as statements
+	 * @return a string without the as statements
+	 */
 	protected static String stripAsStatement(String str) {
-		return str.replaceAll("\\sas[^,]+(,?)", "$1");
+		return str.replaceAll( "\\sas[^,]+(,?)", "$1" );
 	}
 	
-	protected static void insertRowNumberFunction(StringBuilder sb, CharSequence orderby) {
+	/**
+	 * Right after the select statement of a given query we must place the row_number function
+	 * 
+	 * @param sql the initial sql query without the order by clause
+	 * @param orderby the order by clause of the query
+	 */
+	protected static void insertRowNumberFunction(StringBuilder sql, CharSequence orderby) {
 		// Find the end of the select statement
-		int selectEndIndex = sb.indexOf( SELECT ) + SELECT.length();
+		int selectEndIndex = sql.indexOf( SELECT ) + SELECT.length();
 
         // Isert after the select statement the row_number() function:
-        sb.insert( selectEndIndex, " ROW_NUMBER() OVER (" + orderby + ") as __hibernate_row_nr__," );
+        sql.insert( selectEndIndex, " ROW_NUMBER() OVER (" + orderby + ") as __hibernate_row_nr__," );
 	}
 
 	/**