Riok.Mapperly: 3.1.0 : CS8795 Partial method 'xxx' must have an implementation part because it has accessibility modifiers.

[senal]

Dears,

I'm trying out mapperly in one of my projects.
I have an implementation like below. But I'm getting this IDE design time error CS8795 Partial method 'xxx' must have an implementation part because it has accessibility modifiers. on line public static partial Vehicle MapExternalVehicleToVehicle(...)

public static partial class VehicleMapper
{
     // map properties with different names
     [MapProperty(nameof(ExternalVehicle.Make_Year), nameof(Vehicle.MakeYear))]
    
    // map nested props (Engine)
    [MapProperty(nameof(ExternalVehicle.Engine.Engine_Liters), nameof(Vehicle.Engine.Liters))]
    
    // map nested props (Registration)
    [MapProperty(nameof(ExternalVehicle.Registration.Registration_Status), nameof(Vehicle.Registration.Status))]
    
   public static partial Vehicle MapExternalVehicleToVehicle(ExternalVehicle externalVehicle);

}

Any feedback/comment is appreciated.

Thanks

[TimothyMakkison]

Hey, have you tried restarting your ide? Source generators sometimes need a restart before working

Edit: I reread your code and it looks like your MapProperty are invalid.

// map nested props (Engine)
[MapProperty(nameof(ExternalVehicle.Engine.Engine_Liters), nameof(Vehicle.Engine.Liters))]
    
// map nested props (Registration)
[MapProperty(nameof(ExternalVehicle.Registration.Registration_Status), nameof(Vehicle.Registration.Status))]    

// map nested props (Engine)
[MapProperty("Engine.Engine_Liters", "Engine.Liters")]
        
// map nested props (Registration)
[MapProperty("Registration.Registration_Status", "Registration.Status")]   

Your error is due to a common misconception around nameof. nameof will only return the final member and will not print the preceeding ones. nameof(ExternalVehicle.Engine.Engine_Liters) will return "Engine_Liters" instead of "Engine.Engine_Liters"

You should have some other warnings about Mapperly being unable to find various properties.

[senal]

@TimothyMakkison ,
Thank you very much for your prompt feedback,
I did all solutions listed in #519
Thank you very much for pointing me in the right direction of the usage of nameof(...).
I did change the mapping as you suggested.
And tried again restarting the IDE a couple of times. I'm using VS. I even upgrade the IDE to the latest version 17.7.1.
Even I tried downgrading the Mapperly to 3.0.0
Nothing worked for me.

Changed implementation as per your feedback.

public static partial class VehicleMapper
{
    // map properties with different names
    [MapProperty("ExternalVehicle.Make_Year", "Vehicle.MakeYear")]

    // map nested props (Engine)
    [MapProperty("ExternalVehicle.Engine.Engine_Liters", "Vehicle.Engine.Liters")]
    [MapProperty("ExternalVehicle.Engine.Engine_Cylinders", "Vehicle.Engine.Cylinders")]
    [MapProperty("ExternalVehicle.Engine.Engine_Number", "Vehicle.Engine.Number")]

    // map nested props (Registration)
    [MapProperty("ExternalVehicle.Registration.Registration_Status", "Vehicle.Registration.Status")]
    [MapProperty("ExternalVehicle.Registration.Registration_State", "Vehicle.Registration.State")]
    public static partial Vehicle MapExternalVehicleToVehicle(ExternalVehicle externalVehicle);
}

I did write another sample mapping using the Mapper attribute at the class level as follows. but this one is a direct mapping and no nested props involved as in my previous example.

[Mapper]
public static partial class CarMapper
{
    public static partial CarDto MapCarToCarDto(Car car);
}

And that generates the targeted mapping as follows.

public static partial class CarMapper
{
    public static partial global::TryMapperly.Infra.CarDto MapCarToCarDto(global::TryMapperly.Infra.Car car)
    {
        var target = new global::TryMapperly.Infra.CarDto()
        {
            Modal = car.Modal,
            Make = car.Make,
            Manufacture_Year = car.Manufacture_Year,
            Build_Year = car.Build_Year
        };
        return target;
    }
}

Please let me know if you require me to change or try out another option
Appreciate your feedback.

Thanks

[CommonGuy]

Did you add the [Mapper] attribute to your VehicleMapper class?

[TimothyMakkison]

Even I tried downgrading the Mapperly to 3.0.0

Use 3.1.0 instead, 3.0.0 is broken for VS users 😞

Try this:

[Mapper]
public static partial class VehicleMapper
{
    // map properties with different names
    [MapProperty("Make_Year", "MakeYear")]

    // map nested props (Engine)
    [MapProperty("Engine.Engine_Liters", "Engine.Liters")]
    [MapProperty("Engine.Engine_Cylinders", "Engine.Cylinders")]
    [MapProperty("Engine.Engine_Number", "Engine.Number")]

    // map nested props (Registration)
    [MapProperty("Registration.Registration_Status", "Registration.Status")]
    [MapProperty("Registration.Registration_State", "Registration.State")]
    public static partial Vehicle MapExternalVehicleToVehicle(ExternalVehicle externalVehicle);
}

i removed the unneeded types from the start of MapProperty
MapProperty("ExternalVehicle.Registration.Registration_Status", "Vehicle.Registration.Status") will try to find a member ExternalVehicle with the sub members Registration.Registration_Status whereas you want to map the member Registration with the sub member Registration_Status.

[senal]

@TimothyMakkison ,
Your solution fixed my issue.
But I had to initialize the Engine and Registration within the Vehicle constructor. (I was under the impression that Mapperly initiated the nested props which have complex objects).

Below is how the mapping and the vehicle classes are now look like

Also, I have a question about set vs init.
As you can see some of the props in Vehicle class mark with init but in the nested props (Engine and Registration) I had to leave them with get and set ( including props belonging to Engine and Registration because Mapperly failed to map the values to the props.
Do you have any idea why the props with init in nested props didn't get the mapped value? Is it a bug?
Appreciate your feedback.

[Mapper]
public static partial class VehicleMapper
{
    // map properties with different names
    [MapProperty("Make_Year", "MakeYear")]

    // map nested props (Engine)
    [MapProperty("Engine.Engine_Liters", "Engine.Liters")]
    [MapProperty("Engine.Engine_Cylinders", "Engine.Cylinders")]
    [MapProperty("Engine.Engine_Number", "Engine.Number")]

    // map nested props (Registration)
    [MapProperty("Registration.Registration_Plate", "Registration.Plate")]
    [MapProperty("Registration.Registration_Status", "Registration.Status")]
    [MapProperty("Registration.Registration_State", "Registration.State")]
    public static partial Vehicle MapExternalVehicleToVehicle(ExternalVehicle externalVehicle);
}

Vehicle class

public class Vehicle
{
public Vehicle( )
{
	Engine = new Engine();
	Registration = new Registration();
}
public string Make { get; init; } = default!;
public string Model { get; init; } = default!;
public int MakeYear { get; init; } = default!;
public Engine Engine { get; set; }
public Registration Registration { get; set; }

}
public class Engine
{
       public int Cylinders { get; set; } = default!;
    public int Liters { get; set; } = default!;
    public int Number { get; set; } = default!;
 }
public class Registration
{
    public string Plate { get; set; } = default!;
    public string Status { get; set; } = default!;
    public string State { get; set; } = default!;
}

Thanks