Fix encoding for decimals in scientific notation

[kevinkoltz]

Currently Decimal.new("1E+3") (1000.0) gets encoded as 1 in the database. This fixes the encoder to convert the decimal to a string using :normal (without an exponent) instead of using the value.coef which is 1.

iex> Decimal.new("1E+3") |> Map.delete(:__struct__)
%{coef: 1, exp: 3, sign: 1}
iex> Decimal.new("1000") |> Map.delete(:__struct__)
%{coef: 1000, exp: 0, sign: 1}

This was discovered when using Decimal.from_float(1000.0) which results in the exponential representation Decimal.new("1E+3"), which is valid in elixir.

[mjaric]

Then raise"Sign value out of range" for _. It is bad practice to leave uncovered cover cases even tho outer code ATM guarantees it is always 1 or 0.... but one day, someone will make mistake and it will be very hard to understand what is wrong

[kevinkoltz]

Good point, I added the raise

[mjaric]

If you really want to test this correctly this is what it should cover

Expected Result	Precision	Scale	Value
Should decode to 123.45	5	2	123.45
Should decode to -123.45	5	2	-123.45
Should round to 123.46	5	2	123.456
Should round to 123.45	5	2	123.454
Should decode to 99999.99999	10	5	99999.99999
Should decode to exact value	38	18	999999999999999999999.999999999999999999
Should raise an error or truncate	38	18	999999999999999999999.9999999999999999999
Should decode to 9.9	2	1	9.9
Should raise an error or truncate	2	1	9.99
Should decode to exact value	38	0	99999999999999999999999999999999999999
Should decode to NULL	5	2	NULL
Should round to 12300	5	-2	12345
Should round to -0.00	5	2	-0.00001

This is same as it would behave if you try to cast string to decimal with given precision and scale in SQL Server query

[kevinkoltz]

Hey Milan, thanks for the quick review and suggestions. I added all the test cases for inserting into the db, except for the -2 scale one. Let me know if I missed anything. Not sure how to handle the negative scale as the database does not support it from what I can see (SQL error: "Specified scale -2 is invalid."), unless the encoder does?

[mjaric]

@kevinkoltz thank you for contribution ❤️ , could you please check my comments and correct 🙏