Property Control
Facette provides several ways to control which properties appear on the generated DTO and how they're mapped.
Exclude
Pass property names to exclude in the [Facette] constructor. The second parameter is params string[], so you can list them inline:
[Facette(typeof(Employee), "SocialSecurityNumber", "Notes")]
public partial record EmployeeDto;
Or pass an explicit array with the named parameter:
[Facette(typeof(Employee), exclude: new[] { "SocialSecurityNumber", "Notes" })]
public partial record EmployeeDto;
Both forms are equivalent. The generated DTO will have all of Employee's public properties except SocialSecurityNumber and Notes.
Include
Use the Include named parameter to specify an allowlist. Only listed properties will be generated:
[Facette(typeof(Employee),
Include = new[] { "Id", "FirstName", "LastName", "Email" })]
public partial record EmployeeSummaryDto;
Note: You cannot use both
IncludeandExcludeon the same DTO. Doing so produces diagnostic FCT002.
FacetteIgnore
Mark properties you define manually on the DTO to prevent the generator from trying to map them:
[Facette(typeof(Employee), "SocialSecurityNumber")]
public partial record EmployeeDto
{
[FacetteIgnore]
public string FullName { get; set; } = "";
}
Without [FacetteIgnore], the generator would look for a FullName property on Employee and fail. With it, the property is left untouched — you can populate it in an AfterMap hook.
MapFrom
Rename a property or map it from a different source property:
[Facette(typeof(Employee), "SocialSecurityNumber")]
public partial record EmployeeDto
{
[MapFrom("Department")]
public string DepartmentName { get; init; } = "";
}
Here, DepartmentName on the DTO is mapped from the Department property on Employee. Since Department is an enum and DepartmentName is a string, Facette will also auto-detect the enum conversion.
MapFrom also supports dot-notation for flattened paths:
[MapFrom("HomeAddress.State")]
public string State { get; init; } = "";
MapFrom with value conversion
MapFrom has optional Convert and ConvertBack parameters for value conversions:
[MapFrom("HireDate", Convert = nameof(FormatDate), ConvertBack = nameof(ParseDate))]
public string HiredOn { get; init; } = "";
public static string FormatDate(DateTime dt) => dt.ToString("yyyy-MM-dd");
public static DateTime ParseDate(string s) => DateTime.Parse(s);
Referencing non-existent properties
If an Include, Exclude, or MapFrom reference names a property that doesn't exist on the source type, Facette emits a warning diagnostic: