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improve doc of GridFS, emphasize that subsequent call to read() requires to rewind the file with seek(0)

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This commit is contained in:
Bastien Gérard 2019-12-27 10:38:03 +01:00
parent b3dbb87c3c
commit e7c7a66cd1
1 changed files with 17 additions and 2 deletions
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docs/guide/gridfs.rst
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@ -10,8 +10,9 @@ Writing
GridFS support comes in the form of the :class:`~mongoengine.fields.FileField` field
object. This field acts as a file-like object and provides a couple of
different ways of inserting and retrieving data. Arbitrary metadata such as
content type can also be stored alongside the files. In the following example,
a document is created to store details about animals, including a photo::
content type can also be stored alongside the files. The object returned when accessing a
FileField is a proxy to `Pymongo's GridFS <https://api.mongodb.com/python/current/examples/gridfs.html#gridfs-example>`_
In the following example, a document is created to store details about animals, including a photo::
class Animal(Document):
genus = StringField()
@ -34,6 +35,20 @@ field. The file can also be retrieved just as easily::
photo = marmot.photo.read()
content_type = marmot.photo.content_type
.. note:: If you need to read() the content of a file multiple times, you'll need to "rewind"
the file-like object using `seek`::
marmot = Animal.objects(genus='Marmota').first()
content1 = marmot.photo.read()
assert content1 != ""
content2 = marmot.photo.read() # will be empty
assert content2 == ""
marmot.photo.seek(0) # rewind the file by setting the current position of the cursor in the file to 0
content3 = marmot.photo.read()
assert content3 == content1
Streaming
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