Revamp identity value generator to use Statement getGeneratedKeys.

Most JDBC drivers have supported this for ages. No longer do we need the
hackery of turning around and doing another query to obtain generated key
values.

src/main/java/com/samskivert/depot/DepotRepository.java

@@ -5,6 +5,7 @@
 package com.samskivert.depot;
 
 import java.sql.Connection;
+import java.sql.PreparedStatement;
 import java.sql.SQLException;
 import java.sql.Timestamp;
 
@@ -317,15 +318,16 @@ public abstract class DepotRepository
                 Set<String> identityFields = Collections.emptySet();
                 if (_key == null) {
                     // set any auto-generated column values
-                    identityFields = marsh.generateFieldValues(conn, liaison, _result, false);
+                    identityFields = marsh.generateFieldValues(conn, liaison, null, _result, false);
                     updateKey(marsh.getPrimaryKey(_result, false));
                 }
                 builder.newQuery(new InsertClause(pClass, _result, identityFields));
 
-                int mods = builder.prepare(conn).executeUpdate();
+                PreparedStatement stmt = builder.prepare(conn);
+                int mods = stmt.executeUpdate();
                 // run any post-factum value generators and potentially generate our key
                 if (_key == null) {
-                    marsh.generateFieldValues(conn, liaison, _result, true);
+                    marsh.generateFieldValues(conn, liaison, stmt, _result, true);
                     updateKey(marsh.getPrimaryKey(_result, false));
                 }
                 return mods;
@@ -572,17 +574,19 @@ public abstract class DepotRepository
                     Set<String> identityFields = Collections.emptySet();
                     if (_key == null) {
                         // first, set any auto-generated column values
-                        identityFields = marsh.generateFieldValues(conn, liaison, _result, false);
+                        identityFields = marsh.generateFieldValues(
+                            conn, liaison, null, _result, false);
                         // update our modifier's key so that it can cache our results
                         updateKey(marsh.getPrimaryKey(_result, false));
                     }
                     builder.newQuery(new InsertClause(pClass, _result, identityFields));
 
-                    int mods = builder.prepare(conn).executeUpdate();
+                    PreparedStatement stmt = builder.prepare(conn);
+                    int mods = stmt.executeUpdate();
 
                     // run any post-factum value generators and potentially generate our key
                     if (_key == null) {
-                        marsh.generateFieldValues(conn, liaison, _result, true);
+                        marsh.generateFieldValues(conn, liaison, stmt, _result, true);
                         updateKey(marsh.getPrimaryKey(_result, false));
                     }
                     created[0] = true;
@@ -595,16 +599,16 @@ public abstract class DepotRepository
             });
 
         } catch (DuplicateKeyException dke) {
-            // If we got this then the insert failed.
-            // Another node must have done the insert already.
-            // A simple solution here would be to just ignore the DKE and return, because by
-            // definition we're in a race condition and we can just pretend we got in first
-            // but that the other caller did an update afterwards.
+            // If we got this then the insert failed. Another node must have done the insert
+            // already. A simple solution here would be to just ignore the DKE and return, because
+            // by definition we're in a race condition and we can just pretend we got in first but
+            // that the other caller did an update afterwards.
+
             // But: what if non-symmetrical code is being run on the nodes? What if the other node
-            // specifically called insert()? In that case, the other node is expecting
-            // a possible DKE, but this node isn't, and if the other node always calls insert()
-            // then this node would expect its store() to always work and never be overwritten
-            // by the other node. We need to attempt to complete the operation.
+            // specifically called insert()? In that case, the other node is expecting a possible
+            // DKE, but this node isn't, and if the other node always calls insert() then this node
+            // would expect its store() to always work and never be overwritten by the other node.
+            // We need to attempt to complete the operation.
             if (key == null) {
                 throw dke; // how would this even happen?
             }

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

@@ -15,6 +15,7 @@ import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.ResultSetMetaData;
 import java.sql.SQLException;
+import java.sql.Statement;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -653,21 +654,22 @@ public class DepotMarshaller<T extends PersistentRecord> implements QueryMarshal
      * eventual SQL).
      */
     public Set<String> generateFieldValues (
-        Connection conn, DatabaseLiaison liaison, Object po, boolean postFactum)
+        Connection conn, DatabaseLiaison liaison, Statement stmt, Object po, boolean postFactum)
     {
         Set<String> idFields = Sets.newHashSet();
 
         for (ValueGenerator vg : _valueGenerators.values()) {
+            Field field = vg.getFieldMarshaller().getField();
             if (!postFactum && vg instanceof IdentityValueGenerator) {
-                idFields.add(vg.getFieldMarshaller().getField().getName());
+                idFields.add(field.getName());
             }
             if (vg.isPostFactum() != postFactum) {
                 continue;
             }
 
             try {
-                int nextValue = vg.nextGeneratedValue(conn, liaison);
-                vg.getFieldMarshaller().getField().set(po, nextValue);
+                int nextValue = vg.nextGeneratedValue(conn, liaison, stmt);
+                field.set(po, nextValue);
 
             } catch (Exception e) {
                 throw new IllegalStateException(

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

@@ -5,7 +5,9 @@
 package com.samskivert.depot.impl;
 
 import java.sql.Connection;
+import java.sql.ResultSet;
 import java.sql.SQLException;
+import java.sql.Statement;
 
 import com.samskivert.jdbc.DatabaseLiaison;
 import com.samskivert.depot.annotation.GeneratedValue;
@@ -34,10 +36,18 @@ public class IdentityValueGenerator extends ValueGenerator
     }
 
     @Override // from ValueGenerator
-    public int nextGeneratedValue (Connection conn, DatabaseLiaison liaison)
+    public int nextGeneratedValue (Connection conn, DatabaseLiaison liaison, Statement stmt)
         throws SQLException
     {
-        return liaison.lastInsertedId(conn, _dm.getTableName(), _fm.getColumnName());
+        String column = _fm.getColumnName();
+        // if this JDBC driver supports getGeneratedKeys, use it!
+        if (stmt != null && conn.getMetaData().supportsGetGeneratedKeys()) {
+            ResultSet rs = stmt.getGeneratedKeys();
+            if (rs.next()) {
+                return rs.getInt(column);
+            }
+        }
+        return liaison.lastInsertedId(conn, _dm.getTableName(), column);
     }
 
     @Override // from ValueGenerator

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

@@ -64,7 +64,8 @@ public abstract class SQLBuilder
     {
         checkState(_buildVisitor != null, "Cannot prepare query until it's been built.");
 
-        PreparedStatement stmt = conn.prepareStatement(_buildVisitor.getQuery());
+        PreparedStatement stmt = conn.prepareStatement(
+            _buildVisitor.getQuery(), PreparedStatement.RETURN_GENERATED_KEYS);
 
         int argIx = 1;
         for (BuildVisitor.Bindable bindable : _buildVisitor.getBindables()) {

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

@@ -8,6 +8,7 @@ import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
+import java.sql.Statement;
 import java.util.Arrays;
 
 import com.samskivert.depot.annotation.GeneratedValue;
@@ -86,7 +87,7 @@ public class TableValueGenerator extends ValueGenerator
     }
 
     @Override // from ValueGenerator
-    public int nextGeneratedValue (Connection conn, DatabaseLiaison liaison)
+    public int nextGeneratedValue (Connection conn, DatabaseLiaison liaison, Statement stmt)
         throws SQLException
     {
         // TODO: Make this lockless!

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

@@ -46,8 +46,11 @@ public abstract class ValueGenerator
 
     /**
      * Fetch/generate the next primary key value.
+     *
+     * @param stmt if post-factum, the statement that was used to perform the insert which resulted
+     * in the auto-generation of a value, otherwise null.
      */
-    public abstract int nextGeneratedValue (Connection conn, DatabaseLiaison liaison)
+    public abstract int nextGeneratedValue (Connection conn, DatabaseLiaison liaison, Statement stmt)
         throws SQLException;
 
     /**