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Flattening and unflattening

It is pretty common to flatten objects during mapping, eg. Car.Make.Id => CarDto.MakeId. Mapperly tries to figure out flattenings automatically by making use of the PascalCase C# notation. If Mapperly can't resolve the target or source property correctly, it is possible to manually configure it by applying the MapPropertyAttribute by either using the source and target property path names as arrays or using a dot separated property access path string

[MapProperty([nameof(Car.Make), nameof(Car.Make.Id)], nameof(CarDto.MakeId))]
// Or alternatively
[MapProperty("Make.Id", "MakeId")]
// Or
[MapProperty($"{nameof(Make)}.{nameof(Make.Id)}", "MakeId")]
partial CarDto Map(Car car);
info

Unflattening is not automatically configured by Mapperly and needs to be configured manually via MapPropertyAttribute.

Flatten all members of property​

If a property has many members that need to be flattened but that cannot be figured out automatically, this can be configured using the MapNestedProperties attribute. This will bring all sub-members of a specified member into scope as if they were defined on the source object:

[MapProperty([nameof(Car.Engine), nameof(Car.Engine.Horsepower)], nameof(CarDto.Horsepower))]
[MapProperty([nameof(Car.Engine), nameof(Car.Engine.FuelType)], nameof(CarDto.FuelType))]
[MapProperty([nameof(Car.Engine), nameof(Car.Engine.Cylinders)], nameof(CarDto.Cylinders))]
// Is equivalent to:
[MapNestedProperties(nameof(Car.Engine))]
partial CarDto Map(Car car);
info

The nested members have a lower priority than all immediate members of the source object. E.g. if both the Car and the Engine classes in the preceding example contained an Id property, the CarDto.Id property would be mapped from Car.Id.

Similarly, the automatic flattening has precedence over the nested members: CarDto.EngineId would be mapped from Car.Engine.Id rather than Car.Engine.EngineId if Engine contained both.

warning

If multiple MapNestedProperties are defined that contain members that match to the same member on the target object, no guarantees are made as to which source member is chosen. In such a case it is therefore recommended to define the expected property mapping explicitly using a MapProperty attribute.

Full nameof​

Mapperly supports a "fullnameof". It can be used to configure property paths using nameof. Opt-in is done by prefixing the path with @.

[MapProperty(nameof(@Car.Make.Id), nameof(CarDto.MakeId))]
partial CarDto Map(Car car);

nameof(@Car.Make.Id) will result in the property path Make.Id.