92 lines
3.1 KiB
ReStructuredText
92 lines
3.1 KiB
ReStructuredText
======
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GridFS
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======
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.. versionadded:: 0.4
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Writing
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-------
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GridFS support comes in the form of the :class:`~mongoengine.fields.FileField` field
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object. This field acts as a file-like object and provides a couple of
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different ways of inserting and retrieving data. Arbitrary metadata such as
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content type can also be stored alongside the files. The object returned when accessing a
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FileField is a proxy to `Pymongo's GridFS <https://api.mongodb.com/python/current/examples/gridfs.html#gridfs-example>`_
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In the following example, a document is created to store details about animals, including a photo::
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class Animal(Document):
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genus = StringField()
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family = StringField()
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photo = FileField()
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marmot = Animal(genus='Marmota', family='Sciuridae')
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with open('marmot.jpg', 'rb') as fd:
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marmot.photo.put(fd, content_type = 'image/jpeg')
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marmot.save()
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Retrieval
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---------
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So using the :class:`~mongoengine.fields.FileField` is just like using any other
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field. The file can also be retrieved just as easily::
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marmot = Animal.objects(genus='Marmota').first()
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photo = marmot.photo.read()
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content_type = marmot.photo.content_type
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.. note:: If you need to read() the content of a file multiple times, you'll need to "rewind"
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the file-like object using `seek`::
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marmot = Animal.objects(genus='Marmota').first()
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content1 = marmot.photo.read()
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assert content1 != ""
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content2 = marmot.photo.read() # will be empty
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assert content2 == ""
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marmot.photo.seek(0) # rewind the file by setting the current position of the cursor in the file to 0
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content3 = marmot.photo.read()
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assert content3 == content1
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Streaming
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---------
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Streaming data into a :class:`~mongoengine.fields.FileField` is achieved in a
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slightly different manner. First, a new file must be created by calling the
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:func:`new_file` method. Data can then be written using :func:`write`::
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marmot.photo.new_file()
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marmot.photo.write('some_image_data')
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marmot.photo.write('some_more_image_data')
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marmot.photo.close()
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marmot.save()
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Deletion
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--------
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Deleting stored files is achieved with the :func:`delete` method::
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marmot.photo.delete() # Deletes the GridFS document
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marmot.save() # Saves the GridFS reference (being None) contained in the marmot instance
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.. warning::
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The FileField in a Document actually only stores the ID of a file in a
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separate GridFS collection. This means that deleting a document
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with a defined FileField does not actually delete the file. You must be
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careful to delete any files in a Document as above before deleting the
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Document itself.
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Replacing files
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---------------
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Files can be replaced with the :func:`replace` method. This works just like
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the :func:`put` method so even metadata can (and should) be replaced::
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another_marmot = open('another_marmot.png', 'rb')
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marmot.photo.replace(another_marmot, content_type='image/png') # Replaces the GridFS document
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marmot.save() # Replaces the GridFS reference contained in marmot instance
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