PageInfo.hasPreviousPage is false on second page

[daironmichel]

Hi guys,

I'm using graphene==1.1.3 with graphene-django==1.2.1. I'm following the Relay specification and I'm having an issue with pagination on connections.

When paginating forward using the first and after arguments getting the first page is working fine but from the second page forward hasPreviousPage comes back false. For example, on a list of 20 users the endCursor for the first page of 5 items is "abc5". If I ask for the second page of 5 items:

query { users(first: 5, after: "abc5"){ 
  pageInfo {hasPreviousPage hasNextPage startCursor endCursor} 
}}

I get back:

{ "data": { "users": {
    "pageInfo": {
      "hasPreviousPage": false,    <-- This should be true
      "hasNextPage": true,
      "startCursor": "abc6",
       "endCursor": "abc10"
    }
}}}

Same thing happens when paginating backwards but with hasNextPage. When I ask for the ...(last: 5, before: "abc16") then hasNextPage comes back as false.

I think it's a bug on the connection_from_list_slice method in this file. And here is a fragment of the code where I think the problem is:

def connection_from_list_slice(list_slice, args=None, connection_type=None,
                               edge_type=None, pageinfo_type=None,
                               slice_start=0, list_length=0, list_slice_length=None):
    # ...

    first_edge_cursor = edges[0].cursor if edges else None
    last_edge_cursor = edges[-1].cursor if edges else None
    lower_bound = after_offset + 1 if after else 0
    upper_bound = before_offset if before else list_length

    return connection_type(
        edges=edges,
        page_info=pageinfo_type(
            start_cursor=first_edge_cursor,
            end_cursor=last_edge_cursor,
            has_previous_page=isinstance(last, int) and start_offset > lower_bound,
            has_next_page=isinstance(first, int) and end_offset < upper_bound
        )
    )

    # ...