The issue was solved by registering the C++ model with QML as an Instantiable Object Type as described here and then instantiating the model from QML for each new search page, as described in this topic: Is it possible to expose a C++ Class that doesn't have a default constructor to QML ?
Thank you for everyone who tried to help!

@SergeyK12 said in Unite data from two QSqlRelationTableModel into one TableView:

I reimplement the following method of QIdentityProxyModel:

data, index, columnCount
add a private field with QSqlRelationTableModeland the setter.

I suppose there is something alse which i should reimplement to make field in 5 cell editebel. SetData ofcource, but why is it in a gray mode? There is a method which make cells editable?

You can't have a proxy model with 2 source models. internally it will rely on mapFromSource and mapToSource which won't work in your case, start directly from QAbstractItemModel.

The methods you reimplemented are fine, you miss rowCount(), setData() and flags()

use KDE (but its too hard to build a library).

no it's not... detailed instructions to build any tier 1 KDE module (spoiler alert: it's only 9 cmd lines): https://forum.qt.io/topic/76533/copy-selected-rows-of-a-table-to-a-model/12

That's a brilliant and elegant solution!
Thank you bro for spending your precious time with a newbie like me!