04-enum.mdx

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Enum mappings

An enum mapping can be customized by setting the strategy to use. Apply the MapEnumAttribute and pass the strategy to be used for this enum. It is also possible to set the strategy for the entire mapper via the MapperAttribute. Available strategies:

Name	Description
ByValue	Matches enum entries by their values (default)
ByValueCheckDefined	Matches enum entries by their values, checks if the target value is defined
ByName	Matches enum entries by their exact names

The IgnoreCase property allows to opt in for case insensitive mappings (defaults to false).

Applied to all enums mapped inside this mapper.

// highlight-start
[Mapper(EnumMappingStrategy = EnumMappingStrategy.ByName, EnumMappingIgnoreCase = true)]
// highlight-end
public partial class CarMapper
{
    ...
}

Applied to the specific enum mapped by this method. Attribute is only valid on mapping method with enums as parameters.

[Mapper]
public partial class CarMapper
{
    // highlight-start
    [MapEnum(EnumMappingStrategy.ByName, IgnoreCase = true)]
    // highlight-end
    public partial CarMakeDto MapMake(CarMake make);
}

Manually mapped enum values

To explicitly map enum values the MapEnumValueAttibute can be used. Attribute is only valid on mapping methods with enums as parameters.

[Mapper]
public partial class CarMapper
{
    [MapEnum(EnumMappingStrategy.ByName)]
    // highlight-start
    [MapEnumValue(CarFeature.AWD, CarFeatureDto.AllWheelDrive)]
    // highlight-end
    public partial CarFeatureDto MapFeature(CarFeature feature);
}

Fallback value

To map to a fallback value instead of throwing when encountering an unknown value, the FallbackValue property on the MapEnum attribute can be used.

FallbackValue is supported by ByName and ByValueCheckDefined.

[Mapper]
public partial class CarMapper
{
    // highlight-start
    [MapEnum(EnumMappingStrategy.ByName, FallbackValue = CarFeatureDto.Unknown)]
    // highlight-end
    public partial CarFeatureDto MapFeature(CarFeature feature);
}

Strict enum mappings

To enforce strict enum mappings (all source enum values have to be mapped to a target enum value and all target enum values have to be mapped from a source enum value) set the following two EditorConfig settings (see also analyzer diagnostics):

[*.cs]
dotnet_diagnostic.RMG037.severity = error # Unmapped target enum value
dotnet_diagnostic.RMG038.severity = error # Unmapped source enum value