Reraise integrity errors on org name unique contraints as 400

- currently being raised as 500s, but should really be 400s as the request data has the duplicate name

app/organisation/rest.py

@@ -1,4 +1,5 @@
-from flask import Blueprint, jsonify, request
+from flask import Blueprint, current_app, jsonify, request
+from sqlalchemy.exc import IntegrityError
 
 from app.dao.organisation_dao import (
     dao_create_organisation,
@@ -22,6 +23,21 @@ organisation_blueprint = Blueprint('organisation', __name__)
 register_errors(organisation_blueprint)
 
 
+@organisation_blueprint.errorhandler(IntegrityError)
+def handle_integrity_error(exc):
+    """
+    Handle integrity errors caused by the unique contraint on ix_organisation_name
+    """
+    if 'ix_organisation_name' in str(exc):
+        current_app.logger.exception('Unique constraint ix_organisation_name triggered')
+        return jsonify(
+            result='error',
+            message='Organisation name already exists'
+        ), 400
+
+    raise
+
+
 @organisation_blueprint.route('', methods=['GET'])
 def get_organisations():
     organisations = [