Google App Engine - Deployment not working - google-app-engine

Question

I have a Google App Engine project (an API) working against a Google Cloud SQL instance. I have a exact copy of both, the API and the SQL instance, running local.
When I execute the project on development (local), I can explore the API just fine. Yet, when I go on deployment, all the calls return empty.
This is the API code (Java):
#ApiMethod(
name = "test.users.list",
path = "test/users/list",
httpMethod = "get"
)
public UserList testUserList ()
{
UserList users = UserList.getAll();
return users;
}
This is what it returns local:
{
"users": [
{
"id": "3",
"firstName": "Test",
"lastName": "User",
"email": "test#test.com",
"password": "12fc892642c48a8227410f5b6722e1edeeefedfb",
"logins": 0,
"lastLogin": 0,
"roles": [
{
"id": "1",
"name": "user",
"loaded": true
}
],
"fullName": "Test User",
"admin": false,
"lastLoginDat": "1969-12-31T21:00:00.000-03:00",
"loaded": true
},
{
"id": "6",
"firstName": "Test",
"lastName": "User 2",
"email": "test2#test.com",
"password": "c5bc2a33ddffcfb3d61779ab44d7d933e1336b02",
"logins": 0,
"lastLogin": 0,
"fullName": "Test User 2",
"admin": false,
"lastLoginDat": "1969-12-31T21:00:00.000-03:00",
"loaded": true
}
]
}
This is what it returns on the server explorer:
{
"kind": "myapp#usersItem",
"etag": "\"l4AE0sdQvyB-SkumpjWQFJVUZzo/MSGC-asdfasdf\""
}
Some insight:
I have access (through MySQL Workbench) to the local SQL instance and the Google Cloud SQL external instance.
Both, local and external SQL instances, are equal to each other.
I've also guaranteed access to the project I'm using to hit the DB (trough the Google Cloud panel).
I don't really know what to do or check. I've searched for something similar but couldn't find anything related.
Any thought is appreciated.

Answer 1

As Jan pointed out, GAE local and production are two separate stories. But I'm gonna give you something even better than this particular solution, which is the tools to resolve this and further problems:
1. Go to Console > Compute > App Engine > Versions, and make sure the backend version you uploaded is the right one (take a look at the time it was uploaded) and is selected or default.
2. Create an API test method that does a rather basic operation against the DB, but without calling other methods nor using try/catch blocks. You're trying to raise a exception here, if any. All the code you need to hit the DB and return the data should be inside that method.
3. Go to the explorer panel, and execute your test method. If it works, then your problem is not in the connection, but in the logic. Use the same approach of (2) to test the logic.
4. If the method doesn't work, go to: Console > Monitoring > Logs. There you'll find the exception trace.