Attempting to provide more context for some PyOpenWorm connection fai…

…lures (#370, #371)

PyOpenWorm/__init__.py

@@ -191,6 +191,14 @@ def loadData(
     config('rdf.graph').parse(data, format=dataFormat)
 
 
+class ConnectionFailError(Exception):
+    def __init__(self, cause, *args):
+        if args:
+            super(ConnectionFailError, self).__init__('PyOpenWorm connection failed: {}. {}'.format(cause, *args))
+        else:
+            super(ConnectionFailError, self).__init__('PyOpenWorm connection failed: {}'.format(cause))
+
+
 def connect(configFile=False,
             conf=False,
             do_logging=False,
@@ -207,7 +215,7 @@ def connect(configFile=False,
     """
     import logging
     import atexit
-    from .data import Data
+    from .data import Data, ZODBSourceOpenFailError
     m = __import__('__main__')
     if m.connected:
         print ("PyOpenWorm already connected")
@@ -232,7 +240,17 @@ def connect(configFile=False,
         })
 
     Configureable.default = conf
-    conf.openDatabase()
+    try:
+        conf.init_database()
+    except ZODBSourceOpenFailError as e:
+        # Special handling for a common user error with pow which, nonetheless,
+        # may be encontered when *not* using pow
+        if e.openstr.endswith('.pow/worm.db'):
+            raise ConnectionFailError(e, 'Perhaps you need to do a `pow clone`?')
+        raise ConnectionFailError(e)
+    except Exception as e:
+        raise ConnectionFailError(e)
+
     logging.getLogger('PyOpenWorm').info("Connected to database")
 
     atexit.register(disconnect)

PyOpenWorm/data.py

@@ -29,6 +29,10 @@
 _B_UNSET = object()
 
 
+class OpenFailError(Exception):
+    pass
+
+
 class _B(ConfigValue):
 
     def __init__(self, f):
@@ -259,7 +263,12 @@ def init_database(self):
         """ Open the configured database """
         self._init_rdf_graph()
         L.debug("opening " + str(self.source))
-        self.source.open()
+        try:
+            self.source.open()
+        except OpenFailError as e:
+            L.error('Failed to open the data source because: %s', e)
+            raise
+
         nm = NamespaceManager(self['rdf.graph'])
         self['rdf.namespace_manager'] = nm
         self['rdf.graph'].namespace_manager = nm
@@ -577,6 +586,13 @@ def open(self):
         self.graph.open(self.conf['rdf.store_conf'], create=True)
 
 
+class ZODBSourceOpenFailError(OpenFailError):
+    def __init__(self, openstr, *args):
+        super(ZODBSourceOpenFailError, self).__init__('Could not open the database file "{}"'.format(openstr),
+                                                      *args)
+        self.openstr = openstr
+
+
 class ZODBSource(RDFSource):
 
     """ Reads from and queries against a configured Zope Object Database.
@@ -601,7 +617,11 @@ def open(self):
         self.path = self.conf['rdf.store_conf']
         openstr = os.path.abspath(self.path)
 
-        fs = FileStorage(openstr)
+        try:
+            fs = FileStorage(openstr)
+        except FileNotFoundError:
+            raise ZODBSourceOpenFailError(openstr)
+
         self.zdb = ZODB.DB(fs, cache_size=1600)
         self.conn = self.zdb.open()
         root = self.conn.root()