QGIS Atlas pictures from one-to-many relation child layer

Question

The situation:

I create a project in QGIS. I use this project in a Data collection App, so that for each points I make several pictures.

The project is as follow:

• a point layer (parent layer, point - geopackage);
• a table layer (Child layer, no geometry type - geopackage -> attribute field ist set to "Attachment", type is "Image" and the path is set to "Relative to Project Path");
• a relation (Project > Properties > Relations) 1-to-many between the points and the table -> referenced field used an UUID-key;

Relation also describe here: Input App showing only two pictures

My question is:

Once my project / one-to-many relation is set up and I have created few points in the App, how do you access my photos from the child layer in an Atlas/report/Print Layout?

More Details:

I know this is possible for Attribute Tables: in your Print Layout you can check "Generate an atlas" choose your Coverage layer and if this layer has a one-to-many relations set-up you can go under "source" choose "Relation Children" and select the "relation" you want.

What I have tried with:

Add a picture object in the atlas and under "Edit" use a function to "call" the first photo of the child layer. I would then repeat this with 2 or 3 pictures objects each calling a different picture of the child layer.

I know it should be something in this direction:

@project_folder||'\\DCIM\\' = array_get(
    aggregate('TableX',
              'array_agg',
              "Path",
               'Nfoto' =
                attribute(@parent,
                 'fid'))
 ,1)

The aggregate function is giving me Head Hecks and I was hoping for something similar to the attribute table solution...

Answer 1

It has been a long time since I posted this question, but I still would like to thank you, Gabriel De Luca, for your help.

After much more research I found a solution to my problem using the "relation_aggregate" function. It goes as follow:

@project_folder || '//' || array_get( relation_aggregate(relation := '*RELATION'sID*', aggregate := 'array_agg', expression := "path") ,0)

I integrated 4 images in my Atlas and for the second, third and fourth I just change which element my array function calls.

So I get to keep my one to many relation and have the photos integrated in my Atlas. Of course with a one to many relation I can take much more than 4 photos but the extras are not required for my reports.