Compute library book return date?

[dunhill]

Hello people.
I have a library with a column with a loan date. Could you help me with a regular expression that calculates the date to be repaid from the date of the loan?
While i keep doing tests

[chaley]

Originally Posted by dunhill

Hello people.
I have a library with a column with a loan date. Could you help me with a regular expression that calculates the date to be repaid from the date of the loan?
While i keep doing tests

I don't think you mean "regular expression". Those look for patterns in strings and don't do calculation.

What calculation do you want to do? Is it something like ("loan date" + 10 days)?

[dunhill]

Originally Posted by chaley

I don't think you mean "regular expression". Those look for patterns in strings and don't do calculation.

What calculation do you want to do? Is it something like ("loan date" + 10 days)?

Exactly how to know the return date.

[chaley]

Originally Posted by dunhill

Exactly how to know the return date.

You tell us. If I borrow the book on Monday 31/May/2021, when must I return it? If you don't know the answer to that question then there is no way for me to help you.

[ownedbycats]

Unless you always borrow a book for the same duration, you'd probably want a second column with the length of the loan.

[crane3]

Do not believe possible. My local library has a "normal" due date of 3 weeks from date of marking the book for loan & available for download. Then there are also many books that is for loan for just 2 weeks; another case is the the loan time is from a library in the consortium or borrowed from a university by the local library where the loan date is marked as available for download.

So which due date will anyone want the Calibre to "calculate"?

[dunhill]

Originally Posted by ownedbycats

Unless you always borrow a book for the same duration, you'd probably want a second column with the length of the loan.

If I have a column to stipulate the days of the loan, I leave a screenshot.


#fechaprestamo = Loan date
#diasadevolver = Number of days (manual loading)
#adevolver = Date that would have to be returned

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Edited to make the screen captures comply with forum rules.

[dunhill]

Originally Posted by crane3

Do not believe possible. My local library has a "normal" due date of 3 weeks from date of marking the book for loan & available for download. Then there are also many books that is for loan for just 2 weeks; another case is the the loan time is from a library in the consortium or borrowed from a university by the local library where the loan date is marked as available for download.

So which due date will anyone want the Calibre to "calculate"?

And how do you have it configured?

[chaley]

Moderator Notice
Moved posts to a separate thread

[crane3]

I don't have any config for the "due date"; do not see the need for it nor do care; an advanatage of being retired & "on vacation" every day. I read the book after getting it then return it before it is due. Or my library sends a notice a few days before the need to return; did miss once as the email-id was off by 1 character by them.

Only problem occurs when multiple books were reserved & all of the books are available at the same time. Good thing for having multiple tablets so can read multiple books opened at the same time.

[chaley]

Originally Posted by chaley

What calculation do you want to do? Is it something like ("loan date" + 10 days)?

I can't help you until you tell us what calculation you want to do.

Do you want

#adevolver (a computed date) = #fechaprestamo (a date) + #diasadevolver (count of days)

?

[dunhill]

Originally Posted by chaley

I can't help you until you tell us what calculation you want to do.

Do you want

#adevolver (a computed date) = #fechaprestamo (a date) + #diasadevolver (count of days)

?

I'd like

 #fechaprestamo (a date) + #diasadevolver (Manually entered in column) = #adevolver (a computed date)

[chaley]

This should what you want, or at least close to it.

program:
# Calculate number of seconds in a day
	one_day = 60 * 60 * 24;
# Calculate total seconds for days of loan
	loan_seconds = one_day * $#diasadevolver;
# Get the start date in ISO format
	start_day = $$#fechaprestamo;
# Get the "timestamp" for the start date -- number of seconds since epoch
	start_ts = format_date(start_day, 'to_number');
# Add the number of seconds for the days of loan	
	end_ts = start_ts + loan_seconds;
# Convert the timestamp back into a datte
	end_ts = format_date(start_ts, 'from_number');
# Format the date as desired
	end_day = format_date(end_ts, 'yyyy MM dd')

[un_pogaz]

small error in

# Convert the timestamp back into a datte
	end_ts = format_date(start_ts, 'from_number');

Use end_ts instead of start_ts

[chaley]

Originally Posted by un_pogaz

small error in

# Convert the timestamp back into a datte
	end_ts = format_date(start_ts, 'from_number');

Use end_ts instead of start_ts

Thanks for that.

There is an optimization available. 'from_number' also accepts the date format, so you can use:

# Convert the timestamp back into a datte
# Format the date as desired
	format_date(end_ts, 'from_number:yyyy MM dd')

Here is the entire template with un_pogaz's correction and the optimization

program:
# Calculate number of seconds in a day
	one_day = 60 * 60 * 24;
# Calculate total seconds for days of loan
	loan_seconds = one_day * $#diasadevolver;
# Get the start date in ISO format
	start_day = $$#fechaprestamo;
# Get the "timestamp" for the start date -- number of seconds since epoch
	start_ts = format_date(start_day, 'to_number');
# Add the number of seconds for the days of loan	
	end_ts = start_ts + loan_seconds;
# Convert the timestamp back into a date
# Format the date as desired
	format_date(end_ts, 'from_number:yyyy MM dd');