Constraint already exists: CONSTRAINT ON ( user:User ) ASSERT user.username IS UNIQUE

[Antwnina]

I'm trying to run it for the second time and i have constraint exception:
~/Desktop/flasktest/nicolewhite-neo4j-flask-27476c5$ python run.py
Traceback (most recent call last):
File "run.py", line 1, in
from blog import app
File "/home/antonina/Desktop/flasktest/nicolewhite-neo4j-flask-27476c5/blog/init.py", line 4, in
graph.schema.create_uniqueness_constraint("User", "username")
File "/usr/local/lib/python2.7/dist-packages/py2neo/database/init.py", line 775, in create_uniqueness_constraint
{"property_keys": [property_key]})
File "/usr/local/lib/python2.7/dist-packages/py2neo/database/http.py", line 212, in post
raise_from(GraphError(message, **content), error)
File "/usr/local/lib/python2.7/dist-packages/py2neo/util.py", line 122, in raise_from
raise exception
py2neo.database.status.ConstraintViolationException: Constraint already exists: CONSTRAINT ON ( user:User ) ASSERT user.username IS UNIQUE

How it can be solved?

[ScottMcCormack]

A first approach could be to comment out the following three lines in neo4j-flask/blog/__init__.py

graph.schema.create_uniqueness_constraint("User", "username")
graph.schema.create_uniqueness_constraint("Tag", "name")
graph.schema.create_uniqueness_constraint("Post", "id")

So that these are not executed at runtime.

A better approach would be to test the constraints for existence and continue if found. I'm not sure what a best approach would be for managing this in a Flask application.