Revamp OrderBy.random() for postgres compatibility.

src/main/java/com/samskivert/depot/clause/OrderBy.java

@@ -11,6 +11,7 @@ import com.samskivert.util.ArrayUtil;
 import com.samskivert.depot.expression.SQLExpression;
 import com.samskivert.depot.impl.FragmentVisitor;
 import com.samskivert.depot.impl.expression.LiteralExp;
+import com.samskivert.depot.impl.expression.RandomExp;
 
 /**
  *  Represents an ORDER BY clause.
@@ -48,7 +49,7 @@ public class OrderBy implements QueryClause
      */
     public static OrderBy random ()
     {
-        return ascending(new LiteralExp<Object>("rand()"));
+        return ascending(RandomExp.INSTANCE);
     }
 
     /**

src/main/java/com/samskivert/depot/impl/BuildVisitor.java

@@ -48,6 +48,7 @@ import com.samskivert.depot.impl.clause.UpdateClause;
 import com.samskivert.depot.impl.expression.AggregateFun;
 import com.samskivert.depot.impl.expression.IntervalExp;
 import com.samskivert.depot.impl.expression.LiteralExp;
+import com.samskivert.depot.impl.expression.RandomExp;
 import com.samskivert.depot.impl.expression.ValueExp;
 import com.samskivert.depot.impl.expression.AggregateFun.Average;
 import com.samskivert.depot.impl.expression.AggregateFun.Count;
@@ -323,6 +324,12 @@ public abstract class BuildVisitor implements FragmentVisitor<Void>
         return null;
     }
 
+    public Void visit (RandomExp randomExp)
+    {
+        _builder.append("rand()");
+        return null;
+    }
+
     public Void visit (ValueExp<?> valueExp)
     {
         bindValue(valueExp.getValue());

src/main/java/com/samskivert/depot/impl/ExpressionEvaluator.java

@@ -33,6 +33,7 @@ import com.samskivert.depot.impl.clause.DropIndexClause;
 import com.samskivert.depot.impl.clause.UpdateClause;
 import com.samskivert.depot.impl.expression.IntervalExp;
 import com.samskivert.depot.impl.expression.LiteralExp;
+import com.samskivert.depot.impl.expression.RandomExp;
 import com.samskivert.depot.impl.expression.ValueExp;
 import com.samskivert.depot.impl.expression.AggregateFun.Average;
 import com.samskivert.depot.impl.expression.AggregateFun.Count;
@@ -199,6 +200,11 @@ public class ExpressionEvaluator
         return new NoValue("Cannot evaluate LiteralExp: " + literalExp);
     }
 
+    public Object visit (RandomExp randomExp)
+    {
+        return new NoValue("Cannot evaluate RandomExp");
+    }
+
     public Object visit (ValueExp<?> valueExp)
     {
         return valueExp.getValue();

src/main/java/com/samskivert/depot/impl/FragmentVisitor.java

@@ -28,6 +28,7 @@ import com.samskivert.depot.impl.clause.DropIndexClause;
 import com.samskivert.depot.impl.clause.UpdateClause;
 import com.samskivert.depot.impl.expression.IntervalExp;
 import com.samskivert.depot.impl.expression.LiteralExp;
+import com.samskivert.depot.impl.expression.RandomExp;
 import com.samskivert.depot.impl.expression.ValueExp;
 import com.samskivert.depot.impl.expression.AggregateFun.Average;
 import com.samskivert.depot.impl.expression.AggregateFun.Count;
@@ -89,6 +90,7 @@ public interface FragmentVisitor<T>
     public T visit (Join join);
     public T visit (Limit limit);
     public T visit (LiteralExp<?> literal);
+    public T visit (RandomExp random);
     public T visit (ValueExp<?> value);
     public T visit (IntervalExp interval);
     public T visit (WhereClause where);

src/main/java/com/samskivert/depot/impl/PostgreSQLBuilder.java

@@ -29,6 +29,7 @@ import com.samskivert.depot.impl.expression.DateFun.DatePart.Part;
 import com.samskivert.depot.impl.expression.DateFun.DatePart;
 import com.samskivert.depot.impl.expression.DateFun.DateTruncate;
 import com.samskivert.depot.impl.expression.IntervalExp;
+import com.samskivert.depot.impl.expression.RandomExp;
 
 public class PostgreSQLBuilder
     extends SQLBuilder
@@ -39,6 +40,11 @@ public class PostgreSQLBuilder
 
     public class PGBuildVisitor extends BuildVisitor
     {
+        @Override public Void visit (RandomExp randomExp) {
+            _builder.append("random()");
+            return null;
+        }
+
         @Override public Void visit (IntervalExp interval) {
             _builder.append("interval '").append(interval.amount);
             _builder.append(" ").append(interval.unit).append("'");