ctor-mappings.md

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6	Constructor mappings

Constructor mappings

Mapperly supports using parameterized constructors of mapping target types. Mapperly resolves the constructor to be used by the following priorities:

• accessible constructors annotated with MapperConstructor

• if PreferParameterlessConstructors attribute is set to true (default behavior):

  • accessible parameterless constructors.
  • accessible constructors ordered in descending by their parameter count

• If PreferParameterlessConstructors attribute is set to false :

  • Accessible constructors are ordered in descending order by their parameter count.
  • Accessible parameterless constructors are considered afterward.

• constructors with a System.ObsoleteAttribute attribute, unless they have a MapperConstructor attribute

The first constructor which allows the mapping of all parameters is used. Constructor parameters are mapped in a case insensitive matter.

Manual mapping configuration

Manual mapping of source properties to constructor parameters can be configured with the MapProperty attribute. See example below

public class Car
{
    // highlight-start
    public string ModelName { get; set; }
    // highlight-end
}

public record CarDto(string Model);

[Mapper]
public partial class CarMapper
{
    // highlight-start
    [MapProperty(nameof(Car.ModelName), nameof(CarDto.Model))]
    // highlight-end
    public partial CarDto ToDto(Car car);
}

If the target type is a normal class, where the constructor parameter name not necessarily matches the property name, you can identify the correct parameter name using a string literal.

public class Car
{
    public string ModelName { get; set; }
}

public class CarDto
{
    // highlight-start
    public CarDto(string model)
    // highlight-end
    {
        ModelName = model;
    }

    public string ModelName { get; }
}

[Mapper]
public partial class CarMapper
{
    // highlight-start
    [MapProperty(nameof(Car.ModelName), "model")]
    // highlight-end
    public partial CarDto ToDto(Car car);
}