Simple metadata queries. #222

Added support for retrieving metadata that matches all key/value pairs in a query.

briar-core/src/org/briarproject/db/Database.java

@@ -273,6 +273,16 @@ interface Database<T> {
 	 */
 	Collection<MessageId> getMessageIds(T txn, GroupId g) throws DbException;
 
+	/**
+	 * Returns the IDs of any messages in the given group with metadata
+	 * matching all entries in the given query. If the query is empty, the IDs
+	 * of all messages are returned.
+	 * <p/>
+	 * Read-only.
+	 */
+	Collection<MessageId> getMessageIds(T txn, GroupId g, Metadata query)
+			throws DbException;
+
 	/**
 	 * Returns the metadata for all messages in the given group.
 	 * <p/>
@@ -281,6 +291,16 @@ interface Database<T> {
 	Map<MessageId, Metadata> getMessageMetadata(T txn, GroupId g)
 			throws DbException;
 
+	/**
+	 * Returns the metadata for any messages in the given group with metadata
+	 * matching all entries in the given query. If the query is empty, the
+	 * metadata for all messages is returned.
+	 * <p/>
+	 * Read-only.
+	 */
+	Map<MessageId, Metadata> getMessageMetadata(T txn, GroupId g,
+			Metadata query) throws DbException;
+
 	/**
 	 * Returns the metadata for the given message.
 	 * <p/>

briar-core/src/org/briarproject/db/DatabaseComponentImpl.java

@@ -427,6 +427,14 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return db.getMessageMetadata(txn, g);
 	}
 
+	public Map<MessageId, Metadata> getMessageMetadata(Transaction transaction,
+			GroupId g, Metadata query) throws DbException {
+		T txn = unbox(transaction);
+		if (!db.containsGroup(txn, g))
+			throw new NoSuchGroupException();
+		return db.getMessageMetadata(txn, g, query);
+	}
+
 	public Metadata getMessageMetadata(Transaction transaction, MessageId m)
 			throws DbException {
 		T txn = unbox(transaction);

briar-core/src/org/briarproject/db/JdbcDatabase.java

@@ -36,10 +36,12 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Set;
 import java.util.concurrent.locks.Condition;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
@@ -1133,6 +1135,44 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	public Collection<MessageId> getMessageIds(Connection txn, GroupId g,
+			Metadata query) throws DbException {
+		// If there are no query terms, return all messages
+		if (query.isEmpty()) return getMessageIds(txn, g);
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			// Retrieve the message IDs for each query term and intersect
+			Set<MessageId> intersection = null;
+			String sql = "SELECT m.messageId"
+					+ " FROM messages AS m"
+					+ " JOIN messageMetadata AS md"
+					+ " ON m.messageId = md.messageId"
+					+ " WHERE groupId = ? AND key = ? AND value = ?";
+			for (Entry<String, byte[]> e : query.entrySet()) {
+				ps = txn.prepareStatement(sql);
+				ps.setBytes(1, g.getBytes());
+				ps.setString(2, e.getKey());
+				ps.setBytes(3, e.getValue());
+				rs = ps.executeQuery();
+				Set<MessageId> ids = new HashSet<MessageId>();
+				while (rs.next()) ids.add(new MessageId(rs.getBytes(1)));
+				rs.close();
+				ps.close();
+				if (intersection == null) intersection = ids;
+				else intersection.retainAll(ids);
+				// Return early if there are no matches
+				if (intersection.isEmpty()) return Collections.emptySet();
+			}
+			if (intersection == null) throw new IllegalStateException();
+			return Collections.unmodifiableSet(intersection);
+		} catch (SQLException e) {
+			tryToClose(rs);
+			tryToClose(ps);
+			throw new DbException(e);
+		}
+	}
+
 	public Map<MessageId, Metadata> getMessageMetadata(Connection txn,
 			GroupId g) throws DbException {
 		PreparedStatement ps = null;
@@ -1169,6 +1209,18 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	public Map<MessageId, Metadata> getMessageMetadata(Connection txn,
+			GroupId g, Metadata query) throws DbException {
+		// Retrieve the matching message IDs
+		Collection<MessageId> matches = getMessageIds(txn, g, query);
+		if (matches.isEmpty()) return Collections.emptyMap();
+		// Retrieve the metadata for each match
+		Map<MessageId, Metadata> all = new HashMap<MessageId, Metadata>(
+				matches.size());
+		for (MessageId m : matches) all.put(m, getMessageMetadata(txn, m));
+		return Collections.unmodifiableMap(all);
+	}
+
 	public Metadata getGroupMetadata(Connection txn, GroupId g)
 			throws DbException {
 		return getMetadata(txn, g.getBytes(), "groupMetadata", "groupId");