Implement query hints as suggested by bug 306

http://helma.org/bugs/show_bug.cgi?id=306

src/helma/objectmodel/db/DbMapping.java

@@ -903,20 +903,28 @@ public final class DbMapping implements Updatable {
      *  Get a StringBuffer initialized to the first part of the select statement
      *  for objects defined by this DbMapping
      *
+     * @param rel the Relation we use to select. Currently only used for optimizer hints.
+     *            Is null if selecting by primary key.
      * @return the StringBuffer containing the first part of the select query
      *
      * @throws SQLException if the table meta data could not be retrieved
      * @throws ClassNotFoundException if the JDBC driver class was not found
      */
-    public StringBuffer getSelect() throws SQLException, ClassNotFoundException {
+    public StringBuffer getSelect(Relation rel) throws SQLException, ClassNotFoundException {
+        // assign to local variable first so we are thread safe
+        // (selectString may be reset by other threads)
         String sel = selectString;
 
-        if (sel != null) {
+        if (rel == null && sel != null) {
             return new StringBuffer(sel);
         }
 
         StringBuffer s = new StringBuffer("SELECT ");
 
+        if (rel != null && rel.queryHints != null) {
+            s.append(rel.queryHints).append(" ");
+        }
+
         String table = getTableName();
 
         // all columns from the main table
@@ -951,8 +959,11 @@ public final class DbMapping implements Updatable {
             joins[i].renderJoinConstraints(s);
         }
 
-        // cache rendered string for later calls.
+        // cache rendered string for later calls, but only if it wasn't
-        selectString = s.toString();
+        // built for a particular Relation
+        if (rel == null) {
+            selectString = s.toString();
+        }
 
         return s;
     }

src/helma/objectmodel/db/NodeManager.java

@@ -994,9 +994,15 @@ public final class NodeManager {
                      tables.append(',').append(rel.additionalTables);
                 }
 
-                StringBuffer b = new StringBuffer("SELECT ").append(table).append('.')
+                StringBuffer b = new StringBuffer("SELECT ");
-                                                   .append(idfield).append(" FROM ")
+
-                                                   .append(tables);
+                if (rel != null && rel.queryHints != null) {
+                    b.append(rel.queryHints).append(" ");
+                }
+
+                b.append(table).append('.')
+                               .append(idfield).append(" FROM ")
+                               .append(tables);
 
                 if (home.getSubnodeRelation() != null) {
                     // subnode relation was explicitly set
@@ -1089,7 +1095,7 @@ public final class NodeManager {
             Statement stmt = con.createStatement();
             DbColumn[] columns = dbm.getColumns();
             Relation[] joins = dbm.getJoins();
-            StringBuffer q = dbm.getSelect();
+            StringBuffer q = dbm.getSelect(rel);
 
             if (rel.additionalTables != null) {
                  q.append(',').append(rel.additionalTables);
@@ -1171,7 +1177,7 @@ public final class NodeManager {
                 Statement stmt = con.createStatement();
                 DbColumn[] columns = dbm.getColumns();
                 Relation[] joins = dbm.getJoins();
-                StringBuffer q = dbm.getSelect();
+                StringBuffer q = dbm.getSelect(rel);
 
                 if (rel.additionalTables != null) {
                      q.append(',').append(rel.additionalTables);
@@ -1498,7 +1504,7 @@ public final class NodeManager {
 
                 DbColumn[] columns = dbm.getColumns();
                 Relation[] joins = dbm.getJoins();
-                StringBuffer q = dbm.getSelect().append("WHERE ")
+                StringBuffer q = dbm.getSelect(null).append("WHERE ")
                                                 .append(dbm.getTableName())
                                                 .append(".")
                                                 .append(idfield)
@@ -1582,7 +1588,7 @@ public final class NodeManager {
                 Connection con = dbm.getConnection();
                 DbColumn[] columns = dbm.getColumns();
                 Relation[] joins = dbm.getJoins();
-                StringBuffer q = dbm.getSelect();
+                StringBuffer q = dbm.getSelect(rel);
 
                 if (rel.additionalTables != null) {
                      q.append(',').append(rel.additionalTables);

src/helma/objectmodel/db/Relation.java

@@ -93,6 +93,7 @@ public final class Relation {
     String groupbyPrototype;
     String filter;
     String additionalTables;
+    String queryHints;
     Vector filterFragments;
     Vector filterPropertyRefs;
     int maxSize = 0;
@@ -114,6 +115,7 @@ public final class Relation {
         this.filterFragments =     rel.filterFragments;
         this.filterPropertyRefs =  rel.filterPropertyRefs;
         this.additionalTables =    rel.additionalTables;
+        this.queryHints =          rel.queryHints;
         this.maxSize =             rel.maxSize;
         this.constraints =         rel.constraints;
         this.accessName =          rel.accessName;
@@ -292,6 +294,9 @@ public final class Relation {
                 additionalTables = null;
         }
 
+        // get query hints
+        queryHints = props.getProperty(propName + ".hints");
+
         // get max size of collection
         String max = props.getProperty(propName + ".maxSize");