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In Django doc,
select_related()
"follows" foreign-key relationships, selecting additional related-object data when it executes its query.
prefetch_related()
does a separate lookup for each relationship, and does the "joining" in Python.
What does it mean by "doing the joining in python"? Can someone illustrate with an example?
My understanding is that for foreign key relationship, use select_related
; and for M2M relationship, use prefetch_related
. Is this correct?
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What"s the difference between select_related and prefetch_related in Django ORM? __del__: Questions
How can I make a time delay in Python?
5 answers
I would like to know how to put a time delay in a Python script.
Answer #1
import time
time.sleep(5) # Delays for 5 seconds. You can also use a float value.
Here is another example where something is run approximately once a minute:
import time
while True:
print("This prints once a minute.")
time.sleep(60) # Delay for 1 minute (60 seconds).
Answer #2
You can use the sleep()
function in the time
module. It can take a float argument for sub-second resolution.
from time import sleep
sleep(0.1) # Time in seconds
What"s the difference between select_related and prefetch_related in Django ORM? __del__: Questions
How to delete a file or folder in Python?
5 answers
How do I delete a file or folder in Python?
Answer #1
os.remove()
removes a file.os.rmdir()
removes an empty directory.shutil.rmtree()
deletes a directory and all its contents.
Path
objects from the Python 3.4+ pathlib
module also expose these instance methods:
pathlib.Path.unlink()
removes a file or symbolic link.pathlib.Path.rmdir()
removes an empty directory.
We hope this article has helped you to resolve the problem. Apart from What”s the difference between select_related and prefetch_related in Django ORM?, check other __del__-related topics.
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