@Computed enhancements from Zell.

src/java/com/samskivert/jdbc/depot/Computed.java

@@ -20,12 +20,22 @@
 
 package com.samskivert.jdbc.depot;
 
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
 /**
  * Marks a field as computed, meaning it's ignored for schema purposes, it does not directly
  * correspond to a column in a table, and thus its value must be overridden in the {@link Query}.
- * 
- * TODO: Add fieldDefinition="count (*)" or somesuch.
  */
+@Retention(value=RetentionPolicy.RUNTIME)
+@Target(ElementType.FIELD)
 public @interface Computed
 {
+    /** If this value is false, the field is not populated by Depot at all. */
+    boolean required() default true;
+    
+    /** A non-empty value here is taken as literal SQL and used to populate the computed field. */
+    String fieldDefinition() default "";
 }

src/java/com/samskivert/jdbc/depot/FieldMarshaller.java

@@ -109,6 +109,14 @@ public abstract class FieldMarshaller
         return _field;
     }
 
+    /**
+     * Returns the Computed annotation on this field, if any.
+     */
+    public Computed getComputed ()
+    {
+        return _computed;
+    }
+    
     /**
      * Returns the GeneratedValue annotation on this field, if any.
      */
@@ -172,8 +180,9 @@ public abstract class FieldMarshaller
             }
         }
 
+        _computed = field.getAnnotation(Computed.class);
         // if this field is @Computed, it has no SQL definition
-        if (field.getAnnotation(Computed.class) != null) {
+        if (_computed != null) {
             _columnDefinition = null;
             return;
         }
@@ -383,5 +392,6 @@ public abstract class FieldMarshaller
 
     protected Field _field;
     protected String _columnName, _columnDefinition;
+    protected Computed _computed;
     protected GeneratedValue _generatedValue;
 }

src/java/com/samskivert/jdbc/depot/Query.java

@@ -94,18 +94,37 @@ public abstract class Query<T>
         DepotMarshaller<?> mainMarshaller = _classMap.get(_mainType);
         String[] fields = mainMarshaller._allFields;
         StringBuilder query = new StringBuilder("select ");
+        boolean skip = true;
         for (int ii = 0; ii < fields.length; ii ++) {
-            if (ii > 0) {
+            if (!skip) {
                 query.append(", ");
             }
+            skip = false;
+
             FieldOverrideClause clause = _disMap.get(fields[ii]);
             if (clause != null) {
                 clause.appendClause(this, query);
-            } else if (mainMarshaller._fields.get(fields[ii]).getColumnDefinition() != null) {
+                continue;
+            }
+
+            Computed computed = mainMarshaller._fields.get(fields[ii]).getComputed(); 
+            if (computed == null) {
+                // if it's neither overridden nor computed, it's a standard field
                 query.append("T.").append(fields[ii]);
+                continue;
+            }
+
+            // check if the computed field has a literal SQL definition
+            if (computed.fieldDefinition().length() > 0) {
+                query.append(computed.fieldDefinition() + " as " + fields[ii]);
+
+            } else if (!computed.required()) {
+                // or if we can simply ignore the field
+                skip = true;
+
             } else {
                 throw new SQLException(
-                    "Computed field must be overridden [field=" + fields[ii] + "]");
+                    "@Computed(required) field without definition [field=" + fields[ii] + "]");
             }
         }
         query.append("   from " + mainMarshaller.getTableName() + " as T ");