Explicit mapping

Override Configure when names differ or a target value needs business-specific shaping:

[ValiantMapper]
public sealed partial class UserMapper : MapperDefinition<User, UserDto>
{
    public override void Configure(MappingContext<User, UserDto> context)
    {
        context
            .Map(source => source.EmailAddress, target => target.Email)
            .Map(source => $"{source.FirstName} {source.LastName}", target => target.DisplayName)
            .Ignore(target => target.InternalNote);
    }
}

Conditional chains

When applies to every declaration in the same fluent chain:

context
    .Map(source => source.EmailAddress, target => target.Email)
    .Map(source => source.Phone, target => target.Phone)
    .When(source => source.IncludeContactDetails);

Start a new statement when rules need different conditions.

Defaults and fallbacks

Default and Fallback are aliases. The value is used when a rule is skipped by its condition or ignores a null source value:

context.Map(source => source.DisplayName, target => target.DisplayName)
    .When(source => source.IsVisible)
    .Fallback("Hidden user");

Null handling

The mapper-wide default comes from ValiantMappingOptions.NullHandling:

services.AddValiantMappers(options =>
    options.NullHandling = ValiantNullHandling.IgnoreSourceNulls);

Override it per rule:

context.Map(source => source.Nickname, target => target.Nickname)
    .IgnoreNull();

context.Map(source => source.AvatarUrl, target => target.AvatarUrl)
    .MapNull(); // AllowNull() is an alias.

API	Effect
IgnoreNull()	Leave the target value unchanged when the source expression returns null
MapNull()	Assign null, even when mapper options ignore source nulls
AllowNull()	Alias for MapNull()
Default(value)	Use a value when the rule is skipped or a null is ignored
Fallback(value)	Alias for Default(value)

Intentional omissions

Use Ignore to document that a writable or required target member is intentionally not populated:

context.Ignore(target => target.AuditStamp);

This is preferable to suppressing an unmapped-member warning because the decision remains beside the rest of the mapping contract.

Run the conditional and null-policy variants from the Mapping sample catalog.