Omi fails to parse valid(?) string with foreign keys as null

[openenergyplatform]

Omi fails to parse valid(?) string with foreign keys as null

[MGlauer]

"fields": [null] is not something I would consider valid. But this is debatable.
Semantically this means "There is a field and this field is nothing" which is weird.

[christian-rli]

Hmm, that makes sense. I tried to fill out a string that has no foreignKey, but preserving all keys of the metadata json structure. This is not possible however.

When "foreignKeys": [{"fields": [], ... AND
When "reference":{ "fields": null, ...} there is a TypeError ('NoneType' object is not iterable).

When "foreignKeys": [{"fields": [], ... AND
When "reference":{ "fields": [], ...} there is an Exception (Missing reference in foreign key).

With the option of an existing field in which there is nothing:
When "foreignKeys": [{"fields": [null], ... AND
When "reference":{ "fields": [null], ...} there is a key Error: None (which is just logical, I suppose)

With everything just null:
When "foreignKeys": [{"fields": null, ... AND
When "reference":{ "fields": null, ...} there is a TypeError: 'NoneType' object is not iterable (because a list is expected)

Now the way I found around this is to just leave foreignKeys as an empty list "foreignKeys": []. However this eliminates a few json keys from the oemetadata string. I think there is an added value to allowing to preserve those keys even with no foreign keys. The question is how big that value is.

I guess it makes logical sense to have an empty list when there are no foreignKeys. However this does not conform to our approach / our recommendation of just putting null wherever something does not apply. Although, I suppose helper tools could help users steer around this pitfall...

In your opinion @MGlauer , what would a key preserving empty foreignKeys section look like that omi should be able to parse? Or does the concept of an empty nested object not make sense at all?

[MGlauer]

You are right, there is no solution to this problem - and this is intentional. If a list has length > 0 it means that there must be an object in this list. Therefore, if there is an object in the list of foreign keys, there is a foreign key and a foreign key has required fields - e.g. fields and a target table with columns. I am not sure what a foreign key without columns would be. So, yes, such a structure does not make sense

[christian-rli]

OK, thanks for elaborating. I can follow that logic.

From this follows then that strings without a foreign key need to be an empty list like so "foreignKeys": []. Any helper tools should consider this and it should also probably be reflected in the helpful comments section at the bottom of the string. I'll add it to OpenEnergyPlatform/oemetadata#34

Closing this issue and adapting the original string that made me open this issue.