Conditional Mapping & AM0008

AutoMappic v0.5.0 introduces Conditional Member Mapping, allowing you to gate property assignments with custom predicates. This is essential for complex business logic where you only want to map a value if certain criteria are met.

Basic Usage

To add a condition, use the .Condition() option inside a ForMember call:

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<User, UserDto>()
            .ForMember(d => d.AdminStatus, opt => opt.Condition((src, dest) => src.IsAdmin));
    }
}

If the condition evaluates to false, the property on the destination object will not be overwritten.

Dual-Instance Access

Unlike some other mappers, AutoMappic gives you access to both the source and the current state of the destination instance within the condition:

.ForMember(d => d.Score, opt => opt.Condition((src, dest) => src.Score > dest.Score))

This is extremely useful for "Only update if newer/better" logic.

The AM0008 Shield: ProjectTo Protection

One of the most powerful features of AutoMappic is its Build-Time Analytics. Because Condition predicates are emitted as procedural C# code (e.g., if (src.IsAdmin) { ... }), they cannot be translated into SQL by LINQ providers like Entity Framework Core.

To protect you from runtime crashes, AutoMappic includes the AM0008 Diagnostic:

What triggers AM0008?

If you have a profile with a Condition and you attempt to use it inside a .ProjectTo<T>() call, the compiler will issue a warning:

AM0008: ProjectTo may fail at runtime for mapping 'User' -> 'UserDto' because the profile contains procedural logic (Condition) that cannot be translated to SQL.

How to resolve AM0008?

1. Use Map instead of ProjectTo: Fetch the entity first, then map it in-memory.
2. Move logic to the SQL layer: Use a MapFrom with a ternary expression that the LINQ provider can translate (e.g., src => src.IsAdmin ? src.Value : dest.Value).

Performance Note

Because AutoMappic is a Zero-Reflection mapper, your Condition is converted into a direct if statement in the generated code. There is zero overhead from expression tree parsing or delegate invocation at runtime.