How to map multiple properties to one?

[Hantick]

How can i set up the mapping of 3 source properties to one destination property that has required

public class DestinationItem 
{
    public required bool IsAccessible { get; set; }
}

public class BasicItem 
{
    public bool? IsLocked { get; set; }
    public bool? ErrorMessage { get; set; }
    public bool? IsBlocked{ get; set; }
}

I want something like this
[MapProperty([nameof(BasicItem.IsLocked), nameof(BasicItem.ErrorMessage ), nameof(BasicItem.IsBlocked)], [nameof(BookingListItem.IsAccessible)], Use = nameof(MapIsAccessible))]
or
[MapProperty(nameof(BasicItem), [nameof(BookingListItem.IsAccessible)], Use = nameof(MapIsAccessible))]

[UserMapping]
private static bool MapIsAccessible(BasicItem item)
    => (!item.ErrorMessage ?? true) && (!item.IsLocked ?? true) && (!item.IsBlocked?? true);

So basically all those 3 properties are logically combined to IsAccessible property

[latonz]

Starting with Mapperly 3.6.0-next.1 you can use MapPropertyFromSource exactly for this: docs.
Would look sth. like this for you: [MapPropertyFromSource(nameof(DestinationItem.IsAccessible), Use = nameof(MapIsAccessible))].

However it may be easier to just introduce a get only property IsAccessible on your BasicItem.

[hansmbakker]

Is this also the recommended way to map fallback values?

Imagine having a objects like this, where the goal is to have destinationItem.Operator = sourceItem.Operator ?? sourceItem.Owner.

public class DestinationItem
{
    public object Operator  { get; set; }
    public object Owner { get; set; }
}

public class SourceItem 
{
    public object? Operator { get; set; }
    public object Owner { get; set; }
}

[latonz]

Yes yoiu can implement fallbacks like this.