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--- wiki2:python:django:others [2019/02/09 11:49]
alfred creado
+++ wiki2:python:django:others [2020/10/31 20:16] (actual)
@@ Línea 1: / Línea 1: @@
 ====== Other things for Django ======
+===== Messages =====
-  * https://simpleisbetterthancomplex.com/tips/2016/09/06/django-tip-14-messages-framework.html
+  * [[https://simpleisbetterthancomplex.com/tips/2016/09/06/django-tip-14-messages-framework.html|Messages framework]]
+===== Sessions =====
+Add this to the config:
+<code python>
+INSTALLED_APPS = [
+    ...
+    'django.contrib.sessions',
+    ....
+MIDDLEWARE = [
+    ...
+    'django.contrib.sessions.middleware.SessionMiddleware',
+    ....
+</code>
+To use them:
+<code python>
+# Get a session value by its key (e.g. 'my_car'), raising a KeyError if the key is not present
+my_car = request.session['my_car']
+# Get a session value, setting a default if it is not present ('mini')
+my_car = request.session.get('my_car', 'mini')
+# Set a session value
+request.session['my_car'] = 'mini'
+# Delete a session value
+del request.session['my_car']
+</code>
+===== Sending mails =====
+You can send mails with:
+<code>
+from django.core.mail import send_mail
+send_mail('subject', 'message', 'Dont Reply <do_not_reply@domain.com>', ['youremail@example.com'])
+</code>
+===== Load data y dump data from DB =====
+  * https://docs.djangoproject.com/en/2.1/howto/initial-data/
+===== Upload files =====
+You will start having a form:
+<code python>
+from django import forms
+class UploadFileForm(forms.Form):
+    title = forms.CharField(max_length=50)
+    file = forms.FileField()
+</code>
+A view handling this form will receive the file data in ''request.FILES'', which is a dictionary containing a key for each FileField (or ImageField, or other FileField subclass) in the form. So the data from the above form would be accessible as request.FILES['file'].
+The **form that posted the request has the attribute** ''enctype="multipart/form-data"''. Otherwise, request.FILES will be empty.
+For managing this in a view:
+<code>
+def upload_file(request):
+    if request.method == 'POST':
+        form = UploadFileForm(request.POST, request.FILES)
+        if form.is_valid():
+            handle_uploaded_file(request.FILES['file'])
+            return HttpResponseRedirect('/success/url/')
+    else:
+        form = UploadFileForm()
+    return render(request, 'upload.html', {'form': form})
+def handle_uploaded_file(f):
+    with open('some/file/name.txt', 'wb+') as destination:
+        for chunk in f.chunks():  # Looping over UploadedFile.chunks() instead of using read() ensures that large files don’t overwhelm your system’s memory.
+            destination.write(chunk)
+</code>
+If you’re saving a file on **a Model with a FileField**, using a ModelForm makes this process much easier. The file object will be saved to the location specified by the upload_to argument of the corresponding FileField when calling form.save()
+If you are **constructing an object manually**, you can assign the file object from request.FILES to the file field in the model:
+<code python>
+def upload_file(request):
+    if request.method == 'POST':
+        form = UploadFileForm(request.POST, request.FILES)
+        if form.is_valid():
+            instance = ModelWithFileField(file_field=request.FILES['file'])
+            instance.save()
+            return HttpResponseRedirect('/success/url/')
+    else:
+</code>
+When a user uploads a file, Django passes off the file data to an **upload handler** – a small class that handles file data as it gets uploaded. Upload handlers are initially defined in the ''FILE_UPLOAD_HANDLERS'' setting.
+  * ''DEFAULT_FILE_STORAGE''
+  * ''FILE_UPLOAD_HANDLERS'': Which handlers will use Django when receiving a file.
+  * ''FILE_UPLOAD_MAX_MEMORY_SIZE'': When MemoryFileUploadHandler (default) it will upload to memory the file (if it less than this value).
+  * ''FILE_UPLOAD_PERMISSIONS''
+  * ''FILE_UPLOAD_TEMP_DIR'': Directory to store files larger than ''FILE_UPLOAD_MAX_MEMORY_SIZE'' value.
+  * ''MEDIA_ROOT'': Absolute filesystem path to the directory that will hold user-uploaded files.
+  * ''MEDIA_URL'': URL that handles the media served from MEDIA_ROOT, used for managing stored files. It must end in a slash.
+[[https://docs.djangoproject.com/en/3.1/ref/files/uploads/#custom-upload-handlers|You can write custom handlers that customize how Django handles files.]]
+By default, if an uploaded file is smaller than 2.5 megabytes, Django will hold the entire contents of the upload in memory. This means that saving the file involves only a read from memory and a write to disk and thus is very fast. However, if an uploaded file is too large, Django will write the uploaded file to a temporary file stored in your system’s temporary directory.
+Sometimes particular views require **different upload behavior**. In these cases, you can override upload handlers on a per-request basis by modifying ''request.upload_handlers''.
+By default Django stores files locally, using the MEDIA_ROOT and MEDIA_URL settings.
+When you use a FileField or ImageField, Django provides a set of APIs you can use to deal with that file.
+<code python>
+class Car(models.Model):
+    name = models.CharField(max_length=255)
+    price = models.DecimalField(max_digits=5, decimal_places=2)
+    photo = models.ImageField(upload_to='cars')
+car = Car.objects.get(name="57 Chevy")
+car.photo
+# <ImageFieldFile: cars/chevy.jpg>
+car.photo.name
+# 'cars/chevy.jpg'
+car.photo.path
+# '/media/cars/chevy.jpg'
+car.photo.url
+# 'http://media.example.com/cars/chevy.jpg'
+</code>
+You can change the path in this way:
+<code python>
+>>> import os
+>>> from django.conf import settings
+>>> initial_path = car.photo.path
+>>> car.photo.name = 'cars/chevy_ii.jpg'
+>>> new_path = settings.MEDIA_ROOT + car.photo.name
+>>> # Move the file on the filesystem
+>>> os.rename(initial_path, new_path)
+>>> car.save()
+>>> car.photo.path
+'/media/cars/chevy_ii.jpg'
+>>> car.photo.path == new_path
+True
+</code>
+To manipulate images:
+<code python>
+>>> from PIL import Image
+>>> car = Car.objects.get(name='57 Chevy')
+>>> car.photo.width
+
+>>> car.photo.height
+
+>>> image = Image.open(car.photo)
+# Raises ValueError: seek of closed file.
+>>> car.photo.open()
+<ImageFieldFile: cars/chevy.jpg>
+>>> image = Image.open(car.photo)
+>>> image
+<PIL.JpegImagePlugin.JpegImageFile image mode=RGB size=191x287 at 0x7F99A94E9048>
+</code>
+Django delegates decisions about how and where to store files to a file **storage system**. This is the object that actually understands things like file systems, opening and reading files, etc. The default file storage is given by the ''DEFAULT_FILE_STORAGE'' setting.
+You can write your [[https://docs.djangoproject.com/en/3.1/howto/custom-file-storage/|own file storage]].
+You can create an instance of some custom file storage class, or – often more useful – you can use the global default storage system:
+<code>
+>>> from django.core.files.base import ContentFile
+>>> from django.core.files.storage import default_storage
+>>> path = default_storage.save('path/to/file', ContentFile(b'new content'))
+>>> path
+'path/to/file'
+>>> default_storage.size(path)
+
+>>> default_storage.open(path).read()
+b'new content'
+>>> default_storage.delete(path)
+>>> default_storage.exists(path)
+False
+</code>
+The following code will store uploaded files under /media/photos regardless of what your MEDIA_ROOT setting is:
+<code python>
+from django.core.files.storage import FileSystemStorage
+from django.db import models
+fs = FileSystemStorage(location='/media/photos')
+class Car(models.Model):
+    ...
+    photo = models.ImageField(storage=fs)
+</code>
+You can use a callable as the storage parameter for FileField or ImageField. This allows you to modify the used storage at runtime, selecting different storages for different environments, for example:
+<code python>
+def select_storage():
+    return MyLocalStorage() if settings.DEBUG else MyRemoteStorage()
+class MyModel(models.Model):
+    my_file = models.FileField(storage=select_storage)
+</code>
+==== For using S3 or an alterantive service ====
+You need the ''boto3'' and ''django-storages'' packages.
+An example of settings would be...
+<code>
+AWS_ACCESS_KEY_ID = ''
+AWS_SECRET_ACCESS_KEY = ''
+AWS_STORAGE_BUCKET_NAME = 'codi.coop.test'
+AWS_S3_CUSTOM_DOMAIN = f's3.wasabisys.com/{AWS_STORAGE_BUCKET_NAME}'
+AWS_S3_ENDPOINT_URL = 'https://s3.wasabisys.com'
+AWS_DEFAULT_ACL = 'public-read'
+DEFAULT_FILE_STORAGE = 'cc_lib.storages.MediaStorage'
+EXTERNAL_MEDIA_PATH = 'fok/media'
+MEDIA_FILE_OVERWRITE = True
+# AWS_S3_OBJECT_PARAMETERS = {'CacheControl': 'max-age=86400',}
+</code>
+Being the ''cc_lib.storages.MediaStorage'' the next:
+<code python>
+from storages.backends.s3boto3 import S3Boto3Storage
+from django.conf import settings
+class MediaStorage(S3Boto3Storage):
+    location = settings.EXTERNAL_MEDIA_PATH
+    file_overwrite = settings.MEDIA_FILE_OVERWRITE
+</code>
+With this you could create other storages like ''PrivateMediaStorage'' and use it like this:
+<code python>
+class Document(models.Model):
+    uploaded_at = models.DateTimeField(auto_now_add=True)
+    upload = models.FileField()
+class PrivateDocument(models.Model):
+    uploaded_at = models.DateTimeField(auto_now_add=True)
+    upload = models.FileField(storage=PrivateMediaStorage())
+    user = models.ForeignKey(User, related_name='documents')
+</code>
+==== So... ====
+  - Install boto3 and django-storages.
+  - Create your own MediaStorage.
+  - Add the settings.
+  - Configure models.
+  - Remind that forms in template must have the attribute ''enctype=“multipart/form-data”''.
+==== Notes ====
+<code python>
+def upload_path(instance, filename):
+    if instance.type == Resource.ResourceType.PROFILE_PICTURE.value:
+        return f'authors/{instance.owner.uuid}/avatars/{instance.uuid}.png'
+    elif instance.type == Resource.ResourceType.ZINE_COVER.value:
+        return f'zines/{str(instance.related_to)}/cover.jpg'
+</code>

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