validate field mapping when doing an upload and provide feedback about errors before commencing the import about apollo

[dodumosu]

@takinbo please describe the desired result and how it differs from what currently obtains.

[takinbo]

@dodumosu there are fields that must be mapped and those that are optional. Before commencing an import, validate that the required fields have been mapped and if not, display an error so it can be fixed.

[dodumosu]

@takinbo I realized that this isn't as straightforward as it might seem at first blush when I tried implementing it. Since we implemented imports to be used for both new data and updating existing data, checking for required columns in the map is way harder than it might seem, particularly for locations. For participants, the participant ID is always required, but after that, it seems everything else can be optional.

To give a participant example: suppose we have a set of participants for observation, but recruitment is not complete. We might have a set of participant IDs, roles and location IDs, but that's all. Suppose after recruitment is completed, we want to update that set with names and phone numbers. The system should be able to update the data set without requiring the location IDs or roles again. Just the participant ID, name and phone numbers would be specified, and only the first would be required.

For locations, it's similar, except that you might even just want to update a specific location level with specific information, for example, an update to polling station registered voters. You should be able to specify just the polling station ID and the registered voters.

For validation of location mapping, i believe what's necessary is to require that for any level that some column is mapped, the location ID for that level is also mapped. Other than that, I don't think we can put any restrictions on what is required or not.

[takinbo]

@dodumosu testing reveals that this doesn't work as expected. From reading the code, it appears it is supposed to validate the specification of a column for the location type code when a location type name is specified but in my tests, it does not correctly validate.

Also, there doesn't appear to be any validation requiring that the participant id be specified in a participant file upload. I was able to select a file and click upload without specifying a column for the participant id.