Update data file from server code

Anvil Q&A
1

What I’m trying to do:
Hi everyone. I am trying to update (append to) a data file that i have uploaded using the server module. I am unsure exactly what the correct procedure is for editing and overwriting the existing file or if its even possible. My main question here is: what would be the best way to do this and how?
What I’ve tried and what’s not working:
My process is currently as follows:

  • User uploads a file that the server reads and edits after converting to a pandas data frame.
  • The server takes the edited file and appends the data to the end of the existing data file (located on the datafiles) converted into a pandas dataframe.
  • Next i want to overwrite or update the old data file using the newly created pandas dataframe.

The last point is where i get stuck. Should i be following a different process to achieve this or is there a way to code this in the anvil server module?
Thanks in advance!
Code Sample:

  df = process_data(f) # User defined function - returns cleaned pandas data frame
  df_legacy = pd.read_csv(data_files['old_data.csv'], index_col=0)
  df_legacy = df_legacy[df.columns]
  # Concat new processed data with the legacy data
  df_new = pd.concat([df_legacy, df])
  data_files['old_data.csv'] = df_new.to_csv() # Trying to overwrite file - Unsure of correct code or process


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2

Hi @anvil,

You can write to data files but, if it’s a file that’s being updated a lot, then it isn’t recommended to use Data Files as a solution due to a lack of concurrency control. See here for information on how to update files and information on alternatives for files that update regularly:

3

Thanks for the response. Is it maybe better to create a new file in the data files from my data frame and delete the old one? If so, what would be the best method?

4

That would still count as

wouldn’t it? Just by a more roundabout method.

If it’s being updated regularly, why use a file at all, when a database, designed for regular updates, is at hand?

1 Like
5

I will try it that way thank you for your input.