How to simplify transforming entity framework entities to DTOs - entity-framework

Question

I map to a data transformation object when retrieving items from an ASP.NET Web API like so for a list:
public async Task<IList<PromotionDTO>> GetPromotionsList()
{
return await _context.Promotions
.Select(p => new PromotionDTO
{
PromotionId = p.PromotionId,
Is_Active = p.Is_Active,
Created = p.Created,
Title = p.Title,
BusinessName = p.BusinessName,
})
.Where(x => x.Is_Active)
.OrderByDescending(x => x.Created)
.ToListAsync();
}
And like this for getting a single record:
public async Task<PromotionDTO> GetPromotion(int id)
{
return await _context.Promotions
.Select(p => new PromotionDTO
{
PromotionId = p.PromotionId,
Is_Active = p.Is_Active,
Created = p.Created,
Title = p.Title,
BusinessName = p.BusinessName,
})
.Where(x => x.Is_Active && x.PromotionId == id)
.FirstOrDefaultAsync();
}
I'm new to DTO's and I find that I'm using the same DTO transformation code at many places, and was wondering how I can simplify my code to only do this once?

Answer 1

Though it may be enough to map like you've stated, but when your project starts to grow it will just complicated things and cause additional work.
I suggest that you use some kind of mapping library like AutoMapper.
https://github.com/AutoMapper/AutoMapper
static MyRepositoryConstructor()
{
// Define your maps
Mapper.Initialize(cfg => {
cfg.CreateMap<PromotionEntity, PromotionDTO>();
});
}
public async Task<IList<PromotionDTO>> GetPromotionsList()
{
return Mapper.Map<IList<PromotionDTO>>(await _context.Promotions
.Where(x => x.Is_Active)
.OrderByDescending(x => x.Created)
.ToListAsync()
);
}
public async Task<PromotionDTO> GetPromotion(int id)
{
return Mapper.Map<PromotionDTO>(await _context.Promotions
.Where(x => x.Is_Active && x.PromotionId == id)
.FirstOrDefaultAsync()
);
}

Answer 2

One option is to create a method which returns an IQueryable and then use that in each
Private IQueryable<PromotionDTO> Query()
{
return _context.Promotions
.Select(p => new PromotionDTO
{
PromotionId = p.PromotionId,
Is_Active = p.Is_Active,
Created = p.Created,
Title = p.Title,
BusinessName = p.BusinessName,
});
}
public async Task<IList<PromotionDTO>> GetPromotionsList()
{
return await Query()
.Where(x => x.Is_Active)
.OrderByDescending(x => x.Created)
.ToListAsync();
}
public async Task<PromotionDTO> GetPromotion(int id)
{
return await Query()
.Where(x => x.Is_Active && x.PromotionId == id)
.FirstOrDefaultAsync();
}