Add paginated user listing on the db level

src/userdb.js

@@ -8,6 +8,7 @@ exports = module.exports = {
     getByResetToken: getByResetToken,
     getOwner: getOwner,
     getAllWithGroupIds: getAllWithGroupIds,
+    getAllWithGroupIdsPaged: getAllWithGroupIdsPaged,
     getAllAdmins: getAllAdmins,
     add: add,
     del: del,
@@ -115,6 +116,30 @@ function getAllWithGroupIds(callback) {
     });
 }
 
+function getAllWithGroupIdsPaged(page, perPage, callback) {
+    assert.strictEqual(typeof page, 'number');
+    assert.strictEqual(typeof perPage, 'number');
+    assert.strictEqual(typeof callback, 'function');
+
+    var query = `SELECT ${USERS_FIELDS},GROUP_CONCAT(groupMembers.groupId) AS groupIds
+        FROM users LEFT OUTER JOIN groupMembers ON users.id = groupMembers.userId
+        GROUP BY users.id
+        ORDER BY users.username
+        ASC LIMIT ${(page-1)*perPage},${perPage}`;
+
+    database.query(query, function (error, results) {
+        if (error) return callback(new DatabaseError(DatabaseError.INTERNAL_ERROR, error));
+
+        results.forEach(function (result) {
+            result.groupIds = result.groupIds ? result.groupIds.split(',') : [ ];
+        });
+
+        results.forEach(postProcess);
+
+        callback(null, results);
+    });
+}
+
 function getAllAdmins(callback) {
     assert.strictEqual(typeof callback, 'function');