diff --git a/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/DAO.java b/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/DAO.java
index 77a2edc3..2b05c9bc 100644
--- a/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/DAO.java
+++ b/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/DAO.java
@@ -28,6 +28,7 @@
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -92,32 +93,38 @@ static <T, K> List<Stored<T>> put(
 	)
 		throws SQLException
 	{
-		final Map<K, Stored<T>> existing = select.apply(values).stream()
-			.collect(toMap(
-				value -> key.apply(value.value()),
-				value -> value,
-				(a, b) -> b));
+		final List<Stored<T>> result;
 
-		final Map<K, T> actual = values.stream()
-			.collect(toMap(key, value -> value, (a, b) -> b));
+		if (!values.isEmpty()) {
+			final Map<K, Stored<T>> existing = select.apply(values).stream()
+				.collect(toMap(
+					value -> key.apply(value.value()),
+					value -> value,
+					(a, b) -> b));
 
-		final Diff<K, Stored<T>, T> diff = Diff.of(existing, actual);
+			final Map<K, T> actual = values.stream()
+				.collect(toMap(key, value -> value, (a, b) -> b));
 
-		final List<T> missing = diff.missing();
+			final Diff<K, Stored<T>, T> diff = Diff.of(existing, actual);
 
-		final List<Stored<T>> updated = diff
-			.updated((e, a) -> Objects.equals(e.value(), a))
-			.entrySet().stream()
+			final List<T> missing = diff.missing();
+
+			final List<Stored<T>> updated = diff
+				.updated((e, a) -> Objects.equals(e.value(), a))
+				.entrySet().stream()
 				.map(entry -> entry.getKey().map(m -> entry.getValue()))
 				.collect(toList());
 
-		final List<Stored<T>> unchanged = diff
-			.unchanged((e, a) -> Objects.equals(e.value(), a));
+			final List<Stored<T>> unchanged = diff
+				.unchanged((e, a) -> Objects.equals(e.value(), a));
 
-		final List<Stored<T>> result = new ArrayList<>();
-		result.addAll(insert.apply(missing));
-		result.addAll(update.apply(updated));
-		result.addAll(unchanged);
+			result = new ArrayList<>();
+			result.addAll(insert.apply(missing));
+			result.addAll(update.apply(updated));
+			result.addAll(unchanged);
+		} else {
+			result = Collections.emptyList();
+		}
 
 		return result;
 	}
diff --git a/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/LinkDAO.java b/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/LinkDAO.java
index 05b1ba88..eb3568f6 100644
--- a/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/LinkDAO.java
+++ b/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/LinkDAO.java
@@ -22,13 +22,9 @@
 import static java.util.Arrays.asList;
 import static java.util.Collections.singletonList;
 
-import java.net.URI;
 import java.sql.Connection;
 import java.sql.SQLException;
-import java.util.Collections;
 import java.util.List;
-import java.util.function.Function;
-import java.util.stream.Collectors;
 
 import io.jenetics.jpx.Link;
 
@@ -59,6 +55,34 @@ public LinkDAO(final Connection connection) {
 	);
 
 
+	/* *************************************************************************
+	 * SELECT queries
+	 **************************************************************************/
+
+	/**
+	 * Select all available links.
+	 *
+	 * @return all stored links
+	 * @throws SQLException if the select fails
+	 */
+	public List<Stored<Link>> select() throws SQLException {
+		return SQL("SELECT id, href, text, type FROM link")
+			.as(RowParser.list());
+	}
+
+	public List<Stored<Link>> select(final List<Link> links)
+		throws SQLException
+	{
+		final String query =
+			"SELECT id, href, text, type " +
+			"FROM link WHERE href IN ({hrefs})";
+
+		return SQL(query)
+			.on(Param.values("hrefs", links, Link::getHref))
+			.as(RowParser.list());
+	}
+
+
 	/* *************************************************************************
 	 * INSERT queries
 	 **************************************************************************/
@@ -145,73 +169,24 @@ public Stored<Link> update(final Stored<Link> link) throws SQLException {
 	 * @throws SQLException if the insert/update fails
 	 */
 	public List<Stored<Link>> put(final List<Link> links) throws SQLException {
-		return links.isEmpty()
-			? Collections.emptyList()
-			: DAO.put(
-				links,
-				Link::getHref,
-				//list -> selectByHrefs(map(list, Link::getHref)),
-				values -> select(values, Link::getHref, this::selectByHrefs),
-				this::insert,
-				this::update
-			);
+		return DAO.put(
+			links,
+			Link::getHref,
+			this::select,
+			this::insert,
+			this::update
+		);
 	}
 
-	private <A, B> List<Stored<B>> select(
-		final List<B> values,
-		final Function<B, A> mapper,
-		final SQL.Function<List<A>, List<Stored<B>>> select
-	)
-		throws SQLException
-	{
-		final List<A> keys = values.stream()
-			.map(mapper)
-			.collect(Collectors.toList());
-
-		return select.apply(keys);
-	}
 
 	/* *************************************************************************
-	 * SELECT queries
+	 * DELETE queries
 	 **************************************************************************/
 
-	/**
-	 * Select all available links.
-	 *
-	 * @return all stored links
-	 * @throws SQLException if the select fails
-	 */
-	public List<Stored<Link>> select() throws SQLException {
-		return SQL("SELECT id, href, text, type FROM link")
-			.as(RowParser.list());
-	}
-
-	/**
-	 * Selects the links by its hrefs.
-	 *
-	 * @param hrefs the hrefs
-	 * @return the link with the given hrefs currently in the DB
-	 * @throws SQLException if the select fails
-	 */
-	public List<Stored<Link>> selectByHrefs(final List<URI> hrefs)
+	public List<Link> delete(final List<Stored<Link>> links)
 		throws SQLException
 	{
-		final String query =
-			"SELECT id, href, text, type FROM link WHERE href IN ({hrefs})";
-
-		return SQL(query)
-			.on(Param.values("hrefs", hrefs))
-			.as(RowParser.list());
-	}
-
-	/**
-	 * Create a new {@code LinkDAO} for the given connection.
-	 *
-	 * @param conn the DB connection
-	 * @return a new DAO object
-	 */
-	public static LinkDAO of(final Connection conn) {
-		return new LinkDAO(conn);
+		return null;
 	}
 
 }
diff --git a/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/Param.java b/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/Param.java
index 585af36b..78a77246 100644
--- a/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/Param.java
+++ b/jpx.jdbc/src/main/java/io/jenetics/jpx/jdbc/Param.java
@@ -24,6 +24,8 @@
 import static java.util.Objects.requireNonNull;
 
 import java.util.Collection;
+import java.util.List;
+import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.stream.LongStream;
 
@@ -89,13 +91,25 @@ public static Param value(final String name, final Object value) {
 	 * @param values the parameter values
 	 * @return a new parameter object
 	 */
-	public static Param values(
+	public static <T> Param values(
 		final String name,
-		final Collection<? extends Object> values
+		final Collection<T> values
 	) {
 		return new Param(name, values);
 	}
 
+	public static <A, B> Param values(
+		final String name,
+		final Collection<A> values,
+		final Function<A, B> mapper
+	) {
+		final List<B> converted = values.stream()
+			.map(mapper)
+			.collect(Collectors.toList());
+
+		return new Param(name, converted);
+	}
+
 	/**
 	 * Return a new parameter object with the given name and long values.
 	 *