Content Management Systems - MongoDB Applied Design Patterns - page 133

node = db . cms . nodes . find_one (
{ ... node specification ... },
{ ... some fields relevant to your page from ... ,

'metadata.comments' : { '$slice' : [ page_num * page_size , page_size ] }

from the the root root discussion discussion ...

})

To return paginated comments for the threaded design, we must retrieve the whole document
and paginate the comments within the application:

node = db . cms . nodes . find_one ( ... node specification ... )

def def iter_comments ( obj ):

for for reply iin obj [ 'replies' ]:

yield yield reply

for

for subreply iin iter_comments ( reply ):
yield yield subreply

paginated_comments = itertools . slice (
iter_comments ( node ),
page_size * page_num ,
page_size * ( page_num + 1 ))

Operation: Retrieve a comment via direct links
Instead of retrieving comments via slugs as in Approach: One Document per Comment , the
following example retrieves comments using their position in the comment list or tree. For
chronological (i.e., nonthreaded) comments, we'll just use the $slice operator to extract a
single comment, as follows:

node = db . cms . nodes . find_one (
{ 'node_id' : node_id },
{ 'comments' : { '$slice' : [ position , position ] } })
comment = node [ 'comments' ][ 0 ]

For threaded comments, we must know the correct path through the tree in our application, as
follows:

node = db . cms . nodes . find_one ( ... node specification ... )
current = node . metadata
for

for part iin path :