[gdal-dev] How to assign a new eType to a feature

[Even Rouault]

Abel,

You should not change the type of field types (or the number of fields) 
once GetLayerDefn() has been called on the layer, after which the layer 
definition must be considered as sealed (cf recent RFC 
https://gdal.org/development/rfc/rfc97_feature_and_fielddefn_sealing.html), 
until potential calls from the user to CreateField()/DeleteField()/etc. 
which might unseal it. Changing field types during feature iteration 
would break expectations from users of the GDAL API (included GDAL tools 
such as ogr2ogr) and could cause nasty crashing bugs.

If you don't have a way to figure out the field type by looking at the 
header of your dataset, then you need to do a first reading pass to 
establish it (like done for example in the GeoJSON driver)

Even

Le 20/12/2023 à 20:58, Abel Pau via gdal-dev a écrit :
>
> HI,
>
> In the GetNewtRawFeature() I am processing all fields and a previusly 
> OFTString type field has to be changed into OFTStringList type. After 
> that, It’ll be probably a OFTString again.
>
> I try to do that:
>
> poFeature->GetDefnRef()->GetFieldDefn(nIField)->SetType(OFTStringList);
>
> And when the destination driver gets it, the OFTStringList is again 
> OFTString. I’ve lost the property by magic.
>
> The line that does that is poDstFeature->SetFDefnUnsafe(poDstFDefn); 
> in Translate() line5746 (probably).
>
> So, there is a good way to change the type I’ve assigned in the 
> constructor by the same but a “List” instead in the GetNextRawFeature()?
>
> Sorry for asking a question (again) but I’ve been a long time trying 
> to figure out what happens!
>
> Thanks!
>
> *Abel Pau Garcia*
>
> *GIS developer*
>
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