[gdal-dev] Fields of type List to simple fields with N times the feature?

[Even Rouault]

Le 19/01/2024 à 16:54, Abel Pau via gdal-dev a écrit :
>
> Hello,
>
> we have tried to generate some layers from MiraMon to SHP, KML, or 
> GPKG, and we have noticed that they do not support "List" field cases. 
> They give a warning like: "The output driver does not seem to natively 
> support IntegerList type for field “XX”.
>
> It could be interesting if a driver could output a feature with "List" 
> type fields as the same feature repeated as many times as the elements 
> in the List, if the user requests it (via –lco). This would be 
> beneficial to avoid losing elements from fields that are of type List.
>
> The current implementation generates an IntegerList, but this 
> modification could be done.
>
> As we want to export the information somehow, even if it's not 
> perfect, we are wondering which of these solutions we can apply:
>
> 1. (preferable) export N objects, each with a single attribute, not as 
> an "IntegerList" but as N "Integer/Float, etc" objects.
>
> 2. export a single object with a single attribute (which could be 
> chosen with a -lco).
>
> However, we are wondering how we should handle the GetFeatureCount() 
> function in case 1 (from the above).
>
> And we also wonder how to handle the GetNextRawFeature() function. 
> Since this function can indicate that it has returned more than one 
> element (in case 1).
>
Don't complicate your driver. This is just a usage issue of ogr2ogr. As 
hinted by it, you need to pass for example -mapFieldType 
IntegerList=String to ask ogr2ogr to transform IntegerLst fields into string


$ cat test.json
{
"type": "FeatureCollection",
"name": "test",
"features": [
{ "type": "Feature", "properties": { "id": 1, "attr": [2,3] }, 
"geometry": null }
]
}

$ ogr2ogr out.shp test.json -mapFieldType IntegerList=String

$ ogrinfo out.shp -al -q

Layer name: out
Metadata:
   DBF_DATE_LAST_UPDATE=2024-01-19
OGRFeature(out):0
   id (Integer) = 1
   attr (String) = (2:2,3)

Even

> Thanks for taking it in consideration.
>
> *Abel Pau Garcia*
>
> *GIS developer*
>
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