Fixing a bug where the empty prefix's namespace could not be retrieved

- Also, using UTF-8 as the default charset in MySQL schema creation for
  testing on Travis-CI

Resolves: #37

Author: PonteIneptique

.travis.yml

@@ -14,7 +14,7 @@ before_script:
 - sh -c "if [ '$DB' = 'pgsql' ]; then psql -c 'DROP DATABASE IF EXISTS test;' -U postgres;
   psql -c 'create database test;' -U postgres; export DBURI='postgresql+psycopg2://postgres@localhost/test';
   fi"
-- sh -c "if [ '$DB' = 'mysql' ]; then mysql -e 'CREATE DATABASE IF NOT EXISTS test';
+- sh -c "if [ '$DB' = 'mysql' ]; then mysql -e 'CREATE SCHEMA test DEFAULT CHARACTER SET utf8;';
   export DBURI='mysql+mysqldb://test@localhost/test?charset=utf8'; fi"
 - sh -c "if [ '$DB' = 'sqlite' ]; then export DBURI='sqlite:///%(here)s/test.sqlite';
   fi"

CONTRIBUTORS.md

@@ -8,3 +8,4 @@ Contributors to the rdflib-sqlalchemy project:
 * Yves-Marie Haussonne - https://github.com/ymph 
 * Graham Higgins - https://github.com/gjhiggins
 * Ryan Shaw - https://github.com/rybesh
+* Thibault Clérice - https://github.com/ponteineptique

rdflib_sqlalchemy/store.py

@@ -660,7 +660,9 @@ def prefix(self, namespace):
             res = connection.execute(s)
             rt = [rtTuple[0] for rtTuple in res.fetchall()]
             res.close()
-            return rt and rt[0] or None
+            if rt and (rt[0] or rt[0] == ""):
+                return rt[0]
+        return None
 
     def namespace(self, prefix):
         res = None

test/graph_case.py

@@ -22,6 +22,10 @@ class GraphTestCase(unittest.TestCase):
     pizza = URIRef(u"pizza")
     cheese = URIRef(u"cheese")
 
+    namespace_dc = "http://purl.org/dc/elements/1.1/"
+    namespace_dct = "http://purl.org/dc/terms/"
+    namespace_saws = "http://purl.org/saws/ontology#"
+
     def setUp(self, uri="sqlite://", storename=None):
         store = plugin.get(storename, Store)(identifier=self.identifier)
         self.graph = Graph(store, identifier=self.identifier)
@@ -297,6 +301,24 @@ def testStoreLiteralsXmlQuote(self):
         o = objs[0]
         self.assertEquals(o, (bob, says, imtheone))
 
+    def testBindNamespace(self):
+        """ Check that bound namespaced with prefix (including empty ones) are correctly kept """
+        self.graph.bind("", self.namespace_dc)
+        self.graph.bind("dct", self.namespace_dct)
+        self.assertEqual(
+            self.graph.qname(self.namespace_dct + u"title"), "dct:title",
+            "Prefixed namespace should be stored and retrieved"
+        )
+        self.assertEqual(
+            self.graph.qname(self.namespace_dc + u"title"), "title",
+            "Empty prefixes for namespace should be stored and retrieved"
+        )
+        self.assertEqual(
+            self.graph.qname(self.namespace_saws + u"title"), "ns1:title",
+            "Unknown prefixes for namespace should be transformed to nsX"
+        )
+
+
 xmltestdoc = """<?xml version="1.0" encoding="UTF-8"?>
 <rdf:RDF
    xmlns="http://example.org/"