Check whether the module already exists in the database

Signed-off-by: Petr Šabata <contyk@redhat.com>

README.rst

@@ -124,6 +124,7 @@ Possible response codes are for various requests include:
 - HTTP 403 Forbidden - The SCM URL is not pointing to a whitelisted SCM server.
 - HTTP 404 Not Found - The requested URL has no handler associated with it or
   the requested resource doesn't exist.
+- HTTP 409 Conflict - The submitted module's NVR already exists.
 - HTTP 422 Unprocessable Entity - The submitted modulemd file is not valid or
   the module components cannot be retrieved
 - HTTP 500 Internal Server Error - An unknown error occured.

rida.py

@@ -99,6 +99,9 @@ def submit_build():
         mmd.loads(yaml)
     except:
         return "Invalid modulemd", 422
+    if db.session.query(rida.database.Module).filter_by(name=mmd.name,
+        version=mmd.version, release=mmd.release).first():
+        return "Module already exists", 409
     module = rida.database.Module(name=mmd.name, version=mmd.version,
             release=mmd.release, state="init", modulemd=yaml)
     db.session.add(module)