AutoMapper映射问题：如何将SourceEntity列表映射到DestEntity集合

Hey there! Since you're new to AutoMapper, let's break down exactly how to set up the mapping to match the manual logic you've already written.

Step 1: Create a Custom Mapping Profile #

First, you'll need to define a mapping profile that encapsulates the logic to convert SourceEntity to DestEntity. This is where we'll replicate your manual list-checking and object creation flow:

public class EntityMappingProfile : Profile
{
    public EntityMappingProfile()
    {
        CreateMap<SourceEntity, DestEntity>()
            .ForMember(dest => dest.DestinationObjects, opt => opt.MapFrom(src => 
            {
                var destinationItems = new List<SubDestinationEntity>();
                
                // Check if List1 has elements and add the corresponding SubDestinationEntity
                if (src.List1?.Any() == true)
                {
                    destinationItems.Add(new SubDestinationEntity
                    {
                        Title = "Some text 1",
                        Objects = src.List1
                    });
                }
                
                // Repeat the check for List2
                if (src.List2?.Any() == true)
                {
                    destinationItems.Add(new SubDestinationEntity
                    {
                        Title = "Some text 2",
                        Objects = src.List2
                    });
                }
                
                return destinationItems;
            }));
    }
}

Step 2: Initialize AutoMapper with the Profile #

Next, set up your AutoMapper configuration to use this profile, then create a mapper instance for actual conversions:

// Configure AutoMapper with our custom profile
var mapperConfig = new MapperConfiguration(cfg =>
{
    cfg.AddProfile<EntityMappingProfile>();
});

// Optional but recommended: Validate the configuration to catch issues early
mapperConfig.AssertConfigurationIsValid();

// Create the mapper instance
var mapper = mapperConfig.CreateMapper();

Step 3: Use the Mapper in Your Code #

Now you can map your source entity to the destination entity just like you would with standard AutoMapper setups:

// Example source entity with sample data
var source = new SourceEntity
{
    List1 = new List<object> { "Item 1", "Item 2" },
    List2 = new List<object> { "Item 3" }
};

// Perform the mapping
var destination = mapper.Map<DestEntity>(source);

// Result: destination.DestinationObjects will have two SubDestinationEntity instances
// One with Title "Some text 1" (linked to List1) and another with "Some text 2" (linked to List2)

Quick Tips #

• The ?.Any() == true check safely handles null source lists, so you won't run into NullReferenceException if List1 or List2 is uninitialized.
• Using MapFrom lets us inject custom logic directly into the mapping process, which is ideal when standard property-to-property mapping doesn't fit your needs.

内容的提问来源于stack exchange，提问作者Gleb