Conditional mapping

[fubar-coder]

Hi,

let's assume that you have the following object:

class Clazz {
  public int Id { get; set; }
  public required string Name1 { get; set; }
  public required string Name2 { get; set; }
  public bool HasInvoiceAddress { get; set; }
  public string InvoiceName1 { get; set; } = string.Empty;
  public string InvoiceName2 { get; set; } = string.Empty;
}

Now I'd like to create an "update" mapping:

[Mapper(AllowNullPropertyAssignment = false)]
static partial class ClazzMapper {
  public static partial void ApplyUpdate(Clazz source, Clazz target);
}

The problem is that the properties InvoiceName1, etc. should only be copied when HasInvoiceAddress has a value of true.

[Mapper(AllowNullPropertyAssignment = false)]
static partial class ClazzMapper {
  [MappingConditionProperty(nameof(Clazz.InvoiceName1), nameof(Clazz.HasInvoiceAddress))]
  public static partial void ApplyUpdate(Clazz source, Clazz target);
}

Reading the mapping condition from a property might not be enough, when the condition might be more complex. A MappingConditionFromSourceAttribute might be a solution:

[Mapper(AllowNullPropertyAssignment = false)]
static partial class ClazzMapper {
  [MappingConditionFromSource(nameof(Clazz.InvoiceName1), nameof(CopyInvoiceProperties))]
  public static partial void ApplyUpdate(Clazz source, Clazz target);

  private static bool CopyInvoiceProperties(Clazz source) => source.HasInvoiceAddress;
}

It might also be useful to have an override for AllowNullPropertyAssignment on the new MappingConditionFromSourceAttribute and MappingConditionPropertyAttribute, which would force copying the values even though the source value might be null.