Description

It would be very convenient to have possibility of creating proxy models directly from delegate model's instance instead of using SFPM's proxy roles. Moreover SFPM's proxy roles depending on submodel's content cannot be updated properly when submodel is changing.

SubmodelProxyModel {
    id: submodelProxyModel

    sourceModel: tokensModel
    
    delegateModel: SortFilterProxyModel {
        id: delegateRoot
        
        sourceModel: submodel
        
        readonly property alias totalBalanceRole: aggregator.value

        filters: ValueFilter {
            roleName: "address"
            value: selectedAddress
        }
        
        SumAggregator {
            id: aggregator

            model: delegateRoot
            roleName: "balance"
        }
    }
}

It would add totalBalance role to the tokensModel.
New roles can be defined using simple pattern - properties like xxxRole are intended to add xxx role to the top-level model.

It's an alternative to currently used approach based on expression roles and imperative js code iterating over submodels:

FastExpressionRole {
    name: "totalBalance"
    expression: d.getTotalBalance(model.balances, model.decimals, "balance")
    expectedRoles: ["balances", "decimals"]
}

Moreover this expression role based approach is not dynamic, changes in submodel don't trigger changes in a top-level model. Proposed solution, when implemented correctly, can be fully dynamic out of the box.

Depends on: #14389