various additions for multilevel compatibility

lib/levelgraph.js

@@ -110,6 +110,18 @@ module.exports = function levelgraph(leveldb, options) {
   return db;
 };
 
+// patch variables in a query
+function patchQuery(query) {
+  query.forEach(function(e) {
+    utilities.defs.spo.forEach(function(key) {
+      if (typeof e[key] === 'object' &&
+          e[key].constructor !== Variable) {
+        e[key] = new Variable(e[key].name);
+      }
+    });
+  });
+}
+
 searchStream = function(db, options) {
   options = extend({ joinAlgorithm: 'sort' }, options);
 
@@ -119,6 +131,7 @@ searchStream = function(db, options) {
     var that = this
       , result = new PassThrough({ objectMode: true });
 
+    patchQuery(query);
 
     options = extend(joinDefaults, options);
 
@@ -192,7 +205,8 @@ doAction = function(action, leveldb) {
 
 doActionStream = function(type, leveldb) {
 
-  if (!leveldb.createWriteStream) {
+  // also check leveldb.isClient for multilevel compatibility
+  if (!leveldb.createWriteStream || leveldb.isClient) {
     leveldb = levelWriteStream(leveldb);
   }