Issue with DecimalField, max_digits of django models

Question

I have declared below field in models.py.

marks = models.DecimalField(max_digits=2, decimal_places=2, default=3.0)

At backend table structure is :

| Field | Type          | Null | Key | Default | Extra        |
| marks | float(3,1)    | NO   |     | 1.0     |              |

So here default value 3.0 will try to save as 3.00 (decimal places=2) at backend and there will be no space to store left side value 3 right?

For above case,when I give max_digits=3 or decimal_places=1 it is working.

Please help me, whatis exactly happening here from django to mysql db flow?

Answer 1

DecimalField accepts arguments for max_digits which is the total number of digits in a decimal number and for decimal_places which is the number of decimal places.

If you define max_digits to be 3 and decimal_places to be 2, the largest number you can save is 9.99. It has 3 digits and 2 decimal places. If max_digits is for example 5, and decimal_places is 2, the largest number you can save is 999.99.

In your case it doesn't make sense to have maximum 2 digits and to have 2 decimal places, because it can't store 3.00, which has 3 digits. Because 2 digits are already occupied by the decimal places there is no space for digits before the dot. The largest number you can therefore save is 0.99.

Answer 2

these are the definition for max_digits and decimal_places

max_digits The maximum number of digits (those before the decimal point plus those after the decimal point, with leading zeros stripped) permitted in the value.

decimal_places The maximum number of decimal places permitted.