@Computed support from Zell.

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

@@ -0,0 +1,31 @@
+//
+// $Id$
+//
+// samskivert library - useful routines for java programs
+// Copyright (C) 2006 Michael Bayne
+// 
+// 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.jdbc.depot;
+
+/**
+ * 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.
+ */
+public @interface Computed
+{
+}

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

@@ -172,11 +172,23 @@ public class DepotMarshaller<T>
         // generate our full list of fields/columns for use in queries
         _allFields = fields.toArray(new String[fields.size()]);
 
-        // create the SQL used to create and migrate our table
+        // figure out the list of fields that correspond to actual table columns and create the SQL
+        // used to create and migrate our table
+        _columnFields = new String[_allFields.length];
         _columnDefinitions = new String[_allFields.length];
+        int jj = 0;
         for (int ii = 0; ii < _allFields.length; ii++) {
-            _columnDefinitions[ii] = _fields.get(_allFields[ii]).getColumnDefinition();
+            // include all persistent non-computed fields
+            String colDef = _fields.get(_allFields[ii]).getColumnDefinition();
+            if (colDef != null) {
+                _columnFields[jj] = _allFields[ii];
+                _columnDefinitions[jj] = colDef;
+                jj ++;
+            }
         }
+        _columnFields = ArrayUtil.splice(_columnFields, jj);
+        _columnDefinitions = ArrayUtil.splice(_columnDefinitions, jj);
+
         // add the primary key, if we have one
         if (hasPrimaryKey()) {
             String[] indices = new String[_pkColumns.size()];
@@ -306,7 +318,7 @@ public class DepotMarshaller<T>
             columns.add(rs.getString("COLUMN_NAME"));
         }
 
-        for (String fname : _allFields) {
+        for (String fname : _columnFields) {
             FieldMarshaller fmarsh = _fields.get(fname);
             if (columns.contains(fmarsh.getColumnName())) {
                 continue;
@@ -372,9 +384,9 @@ public class DepotMarshaller<T>
         try {
             StringBuilder insert = new StringBuilder();
             insert.append("insert into ").append(getTableName());
-            insert.append(" (").append(StringUtil.join(_allFields, ","));
+            insert.append(" (").append(StringUtil.join(_columnFields, ","));
             insert.append(")").append(" values(");
-            for (int ii = 0; ii < _allFields.length; ii++) {
+            for (int ii = 0; ii < _columnFields.length; ii++) {
                 if (ii > 0) {
                     insert.append(", ");
                 }
@@ -385,7 +397,7 @@ public class DepotMarshaller<T>
             // TODO: handle primary key, nullable fields specially?
             PreparedStatement pstmt = conn.prepareStatement(insert.toString());
             int idx = 0;
-            for (String field :  _allFields) {
+            for (String field :  _columnFields) {
                 _fields.get(field).setValue(po, pstmt, ++idx);
             }
             return pstmt;
@@ -437,7 +449,7 @@ public class DepotMarshaller<T>
     public PreparedStatement createUpdate (Connection conn, Object po, Key key)
         throws SQLException
     {
-        return createUpdate(conn, po, key, _allFields);
+        return createUpdate(conn, po, key, _columnFields);
     }
 
     /**
@@ -599,6 +611,9 @@ public class DepotMarshaller<T>
     /** The persisent fields of our object, in definition order. */
     protected String[] _allFields;
 
+    /** The fields of our object with directly corresponding table columns. */
+    protected String[] _columnFields;
+
     /** The version of our persistent object schema as specified in the class
      * definition. */
     protected int _schemaVersion = -1;

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

@@ -172,6 +172,12 @@ public abstract class FieldMarshaller
             }
         }
 
+        // if this field is @Computed, it has no SQL definition
+        if (field.getAnnotation(Computed.class) != null) {
+            _columnDefinition = null;
+            return;
+        }
+
         // create our SQL column definition
         StringBuilder builder = new StringBuilder();
         if (column != null && !StringUtil.isBlank(column.columnDefinition())) {

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

@@ -91,7 +91,7 @@ public abstract class Query<T>
             throw new RuntimeException("createQuery() called with _mainClass == null");
         }
 
-        DepotMarshaller mainMarshaller = _classMap.get(_mainType);
+        DepotMarshaller<?> mainMarshaller = _classMap.get(_mainType);
         String[] fields = mainMarshaller._allFields;
         StringBuilder query = new StringBuilder("select ");
         for (int ii = 0; ii < fields.length; ii ++) {
@@ -101,8 +101,11 @@ public abstract class Query<T>
             FieldOverrideClause clause = _disMap.get(fields[ii]);
             if (clause != null) {
                 clause.appendClause(this, query);
-            } else {
+            } else if (mainMarshaller._fields.get(fields[ii]).getColumnDefinition() != null) {
                 query.append("T.").append(fields[ii]);
+            } else {
+                throw new SQLException(
+                    "Computed field must be overridden [field=" + fields[ii] + "]");
             }
         }
         query.append("   from " + mainMarshaller.getTableName() + " as T ");

src/java/com/samskivert/jdbc/depot/clause/FieldOverrideClause.java

@@ -63,6 +63,7 @@ public class FieldOverrideClause
     public void appendClause (Query query, StringBuilder builder)
     {
         _override.appendExpression(query, builder);
+        builder.append(" as ").append(_field);
     }
 
     // from QueryClause