OMG I can't believe I didn't think of this earlier: provide fluent builder

methods for expressions. Now you can do FooRecord.BAR.eq(5) instead of new
Equals(FootRecord.BAR, 5), which also saves you the Equals import. Added
methods for operators, some are probably missing and some don't make sense.
I'll fill this out more as I discover where else this style is useful.

src/java/com/samskivert/depot/expression/ColumnExp.java

@@ -23,13 +23,13 @@ package com.samskivert.depot.expression;
 import java.util.Collection;
 
 import com.samskivert.depot.PersistentRecord;
+import com.samskivert.depot.operator.IsNull;
 import com.samskivert.depot.impl.ExpressionVisitor;
 
 /**
  * An expression that unambiguously identifies a field of a class, e.g. GameRecord.itemId.
  */
-public class ColumnExp
-    implements SQLExpression
+public class ColumnExp extends FluentExpression
 {
     /** The name of the column we reference. */
     public final String name;
@@ -51,6 +51,12 @@ public class ColumnExp
         return new ColumnExp(oClass, name);
     }
 
+    /** Returns an {@link IsNull} with this expression as its target. */
+    public IsNull isNull ()
+    {
+        return new IsNull(this);
+    }
+
     // from SQLExpression
     public Object accept (ExpressionVisitor<?> builder)
     {

src/java/com/samskivert/depot/expression/FluentExpression.java

@@ -0,0 +1,174 @@
+//
+// $Id$
+//
+// Depot library - a Java relational persistence library
+// Copyright (C) 2006-2009 Michael Bayne and Pär Winzell
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.samskivert.depot.expression;
+
+import com.samskivert.depot.operator.Add;
+import com.samskivert.depot.operator.And;
+import com.samskivert.depot.operator.Div;
+import com.samskivert.depot.operator.Equals;
+import com.samskivert.depot.operator.GreaterThan;
+import com.samskivert.depot.operator.GreaterThanEquals;
+import com.samskivert.depot.operator.LessThan;
+import com.samskivert.depot.operator.LessThanEquals;
+import com.samskivert.depot.operator.Mul;
+import com.samskivert.depot.operator.NotEquals;
+import com.samskivert.depot.operator.Or;
+import com.samskivert.depot.operator.Sub;
+
+/**
+ * A base class for {@link SQLExpression} implementations that provides a plethora of combinators
+ * for composing expressions.
+ */
+public abstract class FluentExpression
+    implements SQLExpression
+{
+    /** Returns an {@link Equals} with this expression and the supplied target. */
+    public Equals eq (Comparable<?> value)
+    {
+        return new Equals(this, value);
+    }
+
+    /** Returns an {@link Equals} with this expression and the supplied target. */
+    public Equals eq (SQLExpression expr)
+    {
+        return new Equals(this, expr);
+    }
+
+    /** Returns a {@link NotEquals} with this expression and the supplied target. */
+    public NotEquals notEq (Comparable<?> value)
+    {
+        return new NotEquals(this, value);
+    }
+
+    /** Returns a {@link NotEquals} with this expression and the supplied target. */
+    public NotEquals notEq (SQLExpression expr)
+    {
+        return new NotEquals(this, expr);
+    }
+
+    /** Returns a {@link GreaterThan} with this expression and the supplied target. */
+    public GreaterThan greaterThan (Comparable<?> value)
+    {
+        return new GreaterThan(this, value);
+    }
+
+    /** Returns a {@link GreaterThan} with this expression and the supplied target. */
+    public GreaterThan greaterThan (SQLExpression expr)
+    {
+        return new GreaterThan(this, expr);
+    }
+
+    /** Returns a {@link LessThan} with this expression and the supplied target. */
+    public LessThan lessThan (Comparable<?> value)
+    {
+        return new LessThan(this, value);
+    }
+
+    /** Returns a {@link LessThan} with this expression and the supplied target. */
+    public LessThan lessThan (SQLExpression expr)
+    {
+        return new LessThan(this, expr);
+    }
+
+    /** Returns a {@link GreaterThanEquals} with this expression and the supplied target. */
+    public GreaterThanEquals greaterEq (Comparable<?> value)
+    {
+        return new GreaterThanEquals(this, value);
+    }
+
+    /** Returns a {@link GreaterThanEquals} with this expression and the supplied target. */
+    public GreaterThanEquals greaterEq (SQLExpression expr)
+    {
+        return new GreaterThanEquals(this, expr);
+    }
+
+    /** Returns a {@link LessThanEquals} with this expression and the supplied target. */
+    public LessThanEquals lessEq (Comparable<?> value)
+    {
+        return new LessThanEquals(this, value);
+    }
+
+    /** Returns a {@link LessThanEquals} with this expression and the supplied target. */
+    public LessThanEquals lessEq (SQLExpression expr)
+    {
+        return new LessThanEquals(this, expr);
+    }
+
+    /** Returns an {@link And} with this expression and the supplied target. */
+    public And and (SQLExpression expr)
+    {
+        return new And(this, expr);
+    }
+
+    /** Returns an {@link Or} with this expression and the supplied target. */
+    public Or or (SQLExpression expr)
+    {
+        return new Or(this, expr);
+    }
+
+    /** Returns an {@link Add} with this expression and the supplied target. */
+    public Add plus (Comparable<?> value)
+    {
+        return new Add(this, value);
+    }
+
+    /** Returns an {@link Add} with this expression and the supplied target. */
+    public Add plus (SQLExpression expr)
+    {
+        return new Add(this, expr);
+    }
+
+    /** Returns a {@link Sub} with this expression and the supplied target. */
+    public Sub minus (Comparable<?> value)
+    {
+        return new Sub(this, value);
+    }
+
+    /** Returns a {@link Sub} with this expression and the supplied target. */
+    public Sub minus (SQLExpression expr)
+    {
+        return new Sub(this, expr);
+    }
+
+    /** Returns a {@link Mul} with this expression and the supplied target. */
+    public Mul times (Comparable<?> value)
+    {
+        return new Mul(this, value);
+    }
+
+    /** Returns a {@link Mul} with this expression and the supplied target. */
+    public Mul times (SQLExpression expr)
+    {
+        return new Mul(this, expr);
+    }
+
+    /** Returns a {@link Div} with this expression and the supplied target. */
+    public Div div (Comparable<?> value)
+    {
+        return new Div(this, value);
+    }
+
+    /** Returns a {@link Div} with this expression and the supplied target. */
+    public Div div (SQLExpression expr)
+    {
+        return new Div(this, expr);
+    }
+}

src/java/com/samskivert/depot/operator/SQLOperator.java

@@ -28,6 +28,7 @@ import com.google.common.base.Function;
 import com.google.common.base.Predicates;
 import com.google.common.collect.Iterables;
 import com.samskivert.depot.PersistentRecord;
+import com.samskivert.depot.expression.FluentExpression;
 import com.samskivert.depot.expression.SQLExpression;
 import com.samskivert.depot.expression.ValueExp;
 import com.samskivert.depot.impl.ExpressionVisitor;
@@ -150,7 +151,8 @@ public interface SQLOperator extends SQLExpression
         protected SQLExpression _rhs;
     }
 
-    public static abstract class BaseOperator implements SQLOperator
+    public static abstract class BaseOperator extends FluentExpression
+        implements SQLOperator
     {
         public static Function<Object, Long> INTEGRAL = new Function<Object, Long>() {
             public Long apply (Object o) {