minor update

README.rst

@@ -6,7 +6,57 @@ autoimport
 What is autoimport?
 ===================
 
-autoimport is a python3 module and program for importing photos into
+``autoimport`` is a python3 module and program for importing photos into
 a libraries using metadata, namely the name; the date and time of
 the photo, the digitization and the original; the Model and Make
 and the Software used to create the photo.
+
+Usage
+=====
+
+``autoimport`` is used in basically two steps: selecting files to copy/move
+and then actually copying and moving the files. By default the selection step
+is implicit, but it can be run separately using ``autoimport select``. 
+
+``autoimport --help`` gives a list of all available commands and options.
+
+Extended Usage
+==============
+
+Persistent Database
+-------------------
+
+It can be quite useful to run the selection and actual operation separately. 
+For instance, when the actual data is unknow and/or homogenous. To avoid 
+long search times, the intermediate data should then be stored.
+This is done using the ``--storage`` option that specifies a path where
+a sqlite3 database containing the data is stored. 
+
+A typical use case is a collection of RAW and JPEG data, which might be quite big::
+
+	autoimport select images/ --storage=autoimport.db -p jpg --walk
+	autoimport select images/ --storage=autoimport.db -p dng --walk
+
+Then the files can be copied using::
+
+	autoimport copy images/ new_images --storage=autoimport.db
+	rm autoimport.db
+
+without having to re-search all files.
+
+The persistent can also be used to explicitly exclude some files using extra scipts,
+by accessing the database directly. This requires some knowledge in sqlite3 (and maybe
+python3)::
+
+	autoimport select images/ --storage=autoimport.db -p jpg --walk
+
+	sqlite3
+	> .open autoimport.db
+	> DELETE FROM FILES WHERE Model='Nexus 5X';
+	> ^D
+
+	autoimport copy images/ new_images/ --storage=autoimport.db
+
+This example shows how to remove all images made with the Nexus 5X (a cellphone) from the 
+files that are copied. 
+

autoimport/db.py

@@ -85,4 +85,7 @@ def get_persistent_db(path):
             return db
         if(not os.path.exists(os.path.dirname(path))):
             raise IOError("path '{}' does not exist".format(os.path.dirname(path)))
+        db = PersistentDatabase(path)
+        initialize_database(db)
+        return db
     return PersistentDatabase(path)