Using Automap to map ViewModel to Entity in many-to-many relationship - entity-framework-core

Question

I have two entities and their relationship is many to many. The code is like below:
public class Post : Entity
{
//public int Id { get; set; }
public string Title { get; set; }
public string Body { get; set; }
public DateTime CreateTime { get; set; }
public DateTime LastModify { get; set; }
public ICollection<PostTag> PostTags { get; set; }
public int AuthorId { get; set; }
public Author Author { get; set; }
}
public class Tag :Entity
{
//public int Id { get; set; }
public string TagName { get; set; }
public ICollection<PostTag> PostTags { get; set; }
}
public class PostTag :Entity
{
//public int Id { get; set; }
public int PostId { get; set; }
public Post Post { get; set; }
public int TagId { get; set; }
public Tag Tag { get; set; }
}
public class PostViewModel
{
public string Title { get; set; }
public string Body { get; set; }
public DateTime CreateTime { get; set; }
public DateTime LastModify { get; set; }
public int AuthorId { get; set; }
public string AuthorName { get; set; }
public List<TagViewModel> Tags { get; set; }
}
Now, I had created the mapping configure from entity to viewmodel:
CreateMap<Post, PostViewModel>()
.ForMember(dest => dest.AuthorId, opt => opt.MapFrom(src => src.Author.Id))
.ForMember(dest => dest.Tags, opt => opt.MapFrom(src => src.PostTags))
.ForMember(dest => dest.AuthorName, opt => opt.MapFrom(src => src.Author.User.LastName))
.ForMember(dest => dest.Body, opt => opt.MapFrom(src => src.Body))
.ForMember(dest => dest.Title, opt => opt.MapFrom(src => src.Title))
.ForMember(dest => dest.CreateTime, opt => opt.MapFrom(src => src.CreateTime))
.ForMember(dest => dest.LastModify, opt => opt.MapFrom(src => src.LastModify))
.ForMember(dest => dest.Tags, opt => opt.MapFrom(src => src.PostTags.Select(y => y.Tag).ToList()));
My question is, when I receive a PostViewModel like:
public async Task<IActionResult> Post([FromBody] PostViewModel postViewModel)
{
}
how can I map the PostViewModel to Post? And I want to create an Entity from the PostViewModel and add them, which is post, tag(if not exist) and postTag relationship, into DbContext, what should I do?
I am pretty new to automapper and this is my first question, I hope I am doing right thing and I really appreciate your answer and guid for how to ask.

Answer 1

You have two choices I think.
1) Reverse mapping
You can just add .ReverseMap() to the end of your mapping config
CreateMap<Post, PostViewModel>()
.ForMember(dest => dest.AuthorId, opt => opt.MapFrom(src => src.Author.Id))
...
.ForMember(dest => dest.Tags, opt => opt.MapFrom(src => src.PostTags.Select(y => y.Tag).ToList()))
.ReverseMap();
2) You can define a new configuration for PostViewModel to Post
CreateMap<PostViewModel, Post>()
.ForMember(dest => dest.Author.Id, opt => opt.MapFrom(src => src.AuthorId))
...etc
Then Mapper.Map<Post>(postViewModel)