You could add "1-" to "Jan-2019" to create "1-Jan-2019", use the DateTimeConverter to create "20190101" and then remove the last 2 characters with a SubstringExtractor to have "201901" as a result.

Thanks for your suggestions. Had thought of something similar with string transformers. However, I was not sure whether that would cause issues later when I need to use the date.

Would the string "201901" obtained this way be treated as Date by FME if I need to use it later say to calculate number of months between two dates ? I could again convert the dates back to "20190101" by adding "1". But was wondering if there is a simpler way.

If I try to add a year to "201901" the DateTimeCalculator returns a Rejected Feature. From the log:

DateTimeCalculator: Failed to evaluate expression '@DateTimeAdd(201901,P1Y)'.  Result is set to null

So apparently "201901" is not a valid date in FME.

Yes, unfortunately, it looks like FME won't support what you ask. From the documentation:

...temporal information must satisfy the following requirements, or else it is rejected and the result is set to null:
 
- Year, month, day are provided together, in any order, through a combination of format flags such as %Y-%m-%d.

As Niels says, the only good way is to add 01 as the day. However, you don't need to use any extra transformers to do that; you can simply set the DateTimeConverter input format to 01-%b-%Y and the output format to %Y%m

You'd need to keep the day to use the DateTimeCalculator, unfortunately. But I'll raise this with our developers because I think "month-year" date support would be useful.

...temporal information must satisfy the following requirements, or else it is rejected and the result is set to null:
 
- Year, month, day are provided together, in any order, through a combination of format flags such as %Y-%m-%d.

So I suggested that we allow partial dates in the DateTimeConverter.

However, it doesn't mean that we'd have full native support for partial dates. i.e. the DateTimeCalculator won't handle them (because it doesn't have a field for flags like the Converter) and writers won't handle them either (you could write to a string, but not to a date/datetime field).

The issue is filed as FMEENGINE-10149

What I might do is try to create a custom transformer for the hub that handles partial date calculations (a PartialDateTimeCalculator as it were).

Thanks @mark2atsafe​  for raising the issue. It would be nice to have partial dates supported.

Thanks @nielsgerrits​ for the suggestions.

The dates in my datasets are associated with monthly values and having a specific day (eg. 1st of the month) doesn't quite represent the relationship in the data. This would likely confuse someone looking at the data.

However, for now I have added 01 as the day to be able to use the text values as Date.

Thanks for the suggestions.