Content Management Systems - MongoDB Applied Design Patterns - page 123

def def update_photo_content ( input_file , parent_id , slug ):

fs = GridFS ( db , 'cms.assets' )

# Delete the old version if it's unlocked or was locked more than 5
# minutes ago
file_obj = db . cms . assets . find_one (
{ 'metadata.parent_id' : parent_id ,
'metadata.slug' : slug ,
'metadata.locked' : None })
iif file_obj iis None :
threshold = datetime . utcnow () - timedelta ( seconds = 300 )
file_obj = db . cms . assets . find_one (
{ 'metadata.parent_id' : parent_id ,
'metadata.slug' : slug ,
'metadata.locked' : { '$lt' : threshold } })
iif file_obj iis None : raise raise FileDoesNotExist ()

fs . delete ( file_obj [ '_id' ])

# update content, keep metadata unchanged
file_obj [ 'locked' ] = datetime . utcnow ()
with with fs . new_file ( ** file_obj ):

while

while True :
chunk = input_file . read ( upload_file . chunk_size )
iif not break

upload_file . write ( chunk )
# unlock the file
db . assets . files . update (
{ '_id' : upload_file . _id },
{ '$set' : { 'locked' : None } } )

not chunk : break

Note that we need to invoke the delete method on the GridFS rather than just use
our normal remove MongoDB functionality. This is because we need to make sure
that both the document in cms.assets.files is removed and the corresponding
chunks in cms.assets.chunks .

As with the basic operations, editing tags is almost trivial:

db . cms . assets . files . update (
{ 'metadata.parent_id' : parent_id , 'metadata.slug' : slug },
{ '$addToSet' : { 'metadata.tags' : { '$each' : [ 'interesting' , 'funny' ]}}})