EF.Functions: Translating ISDATE to SQL Server

[ralmsdeveloper]

Implementation for #8488

As this function returns 0/1.
So I thought it would be better to make it Boolean.

https://docs.microsoft.com/en-us/sql/t-sql/functions/isdate-transact-sql?view=sql-server-2017

cc/ @divega @smitpatel

[ralmsdeveloper]

@AndriySvyryd

Can you tell me why my tests broke?

I did not find anything, only messages CI.

[AndriySvyryd]

Microsoft.EntityFrameworkCore.SqlServerDbFunctionsExtensions.IsDate[expression] is missing NotNull annotation

[smitpatel]

@divega - Should this return bool or int. SqlServer ISDATE returns int

[ralmsdeveloper]

Note: as I reported here: #16471 (comment).
It would be much nicer and semantic to use Boolean, since ISDATE returns only 0/1, but if we should follow exactly what SQLServer tells us, we should return an integer, but I would be happy if it was boolean already that makes more sense.

[smitpatel]

Only waiting for @divega to decide on return type now.

[divega]

It appears that functions like ISDATE and ISNUMERIC only return int for historical reasons. All other things being equal, bool seems a better type for the method in .NET, unless there are drawbacks with it.

[smitpatel]

Can we also have a positive test which recognize and returns true. In projection & where both.

[smitpatel]

Validate if the given string is a valid date.

[smitpatel]

true for valid date and false otherwise.

[mburbea]

Sql server's ISDATE function is limited to formats supported by DateTime and will reject valid dates that can be converted to types introduced in sql server 2008 (datetime2,datetimeoffset,date and time). A datetime2(3) is basically a better datetime than the datetime object.

select priorTo1753=isDate('1000-01-01')
         ,highPrecision = isDate('2019-07-15T00:00:00.1234')

For my money, a better test might be to use the try_* of functions and test against null.

[ralmsdeveloper]

@smitpatel I made the requested adjustments and also the rebase.

[smitpatel]

@ralmsdeveloper - Thanks.