Support for cursor based pagination

[mpgalaxy]

Hi,

how can I use cursor based pagination (page=page, per_page=...) with your library ? I can't modify the mongo request using something like this:

def resolve_users(self, info):
    	return list(UserModel.objects.find({...}).sort(...).limit(limit))

because then I get 'QuerySet' object has no attribute 'find'

Please provide information regarding this functionality or implement this feature.

[stefanvanburen]

try using limit with skip:

def resolve_users(self, info):
    	return list(UserModel.objects(query).sort(...).skip(x).limit(limit))

you'll want to calculate the skip based on the page number and page size, of course

[mpgalaxy]

@svanburen : This is what I try to avoid. I want to use cursor based pagination with page and per_page params without the need of count(). I tried to use this library with pagination by flask_mongoengine, but it doesn't work. It inserts first:1 in the query which results in a Not a query object error:

def resolve_users(self, info, page=None):
    	return list(UserModel.objects(query).paginate(page=page, per_page=4))

If I try to query with skip and limit, I also get this type of error:

def resolve_users(self, info):
        return list(UserModel.objects(query).skip(5).limit(3))

Results in:

graphql.error.located_error.GraphQLLocatedError: Not a query object: 
    query {
        users {
            firstName,
            lastName
        }
    }
. Did you intend to use key=value?

Running the same query with .all() works perfectly fine.
The .objects(query) part seems to be the problem. Is there another way to interact with the mongo query using default mongo functions ?

[stefanvanburen]

It looks like in your case, you probably just want to omit the "query" parameter to .objects:

def resolve_users(self, info):
        return list(UserModel.objects().skip(5).limit(3))

[mpgalaxy]

@svanburen : This works, but how can I do a find() before limit ?
I need to be able to do a

return list(UserModel.objects().find({'_id' > last_id}).sort(sort).limit(per_page))

How can I do this with this library ?

[stefanvanburen]

@mpgalaxy perhaps something like this?:

return list(UserModel.objects(id__gte=last_id).sort(sort).limit(per_page))

for reference: http://docs.mongoengine.org/guide/querying.html#query-operators

also, I see that you're using '_id' - you may want to replace the id__gte above with whatever the primary key is defined in your UserModel (I put id above, but you'll want to replace that - so if it's user_id, do this:

return list(UserModel.objects(user_id__gte=last_id).sort(sort).limit(per_page))

)

hopefully that helps!

[mpgalaxy]

Thank you very much! :) I will give it a try tomorrow.
Currently I implemented pagination via skip and limit, which is suitable for small datasets:

def resolve_users(self, info, page=None, per_page=None):
        if page <= 0 or per_page <= 0:
            raise Exception("Values of page and per_page must be >0!")
        elif page == 1:
            return list(UserModel.objects.limit(per_page))
        else:
            return list(UserModel.objects.skip((page-1)*per_page).limit(per_page))

I have to make sure that the ids are sorted ascending. Currently the library returns them sorted ascending, but an option for that would be nice. ;) I'll report back on my results.

BTW: How can I send a 404 response with this lib ?
Throwing an Exception is not the best way to do this, because you still get status 200. ;)

BTW2: Is there a mutation example for flask ? In the example section I couldn't find one and I can't save my created user to the db, because it is a User object.

Thanks again and best regards ;)

[stefanvanburen]

I don't have a great answer for you for flask / 404s; typically in GraphQL rather than setting a HTTP response code you'll populate the errors dict, and I'd imagine the flask mutations wouldn't be so far from the other examples.

For sorting, you can use order_by to sort:

return list(UserModel.objects(user_id__gte=last_id).order_by(...).limit(per_page))

good luck!

[mpgalaxy]

Hi, thank you very much, you really helped me a lot. I think I can close this issue now. ;)