Missing type map configuration or unsupported mapping.while trying to assign the data to DTO object - asp.net-core-3.1

Question

I am using AutoMapper.Extensions.Microsoft.DependencyInjection. I am using the Automapper NuGet package: AutoMapper.Extensions.Microsoft.DependencyInjection (7.0.0) for ASP.NET Core 3.1 application.
Here goes my domain object: file ResourceGroup.cs
public class ResourceGroups
{
public string id
{
get;
set;
}
public int ResourceGroupId
{
get;
set;
}
public bool IsPublished
{
get;
set;
}
public int? Position
{
get;
set;
}
public string CreatedBy
{
get;
set;
}
public string CreatedDate
{
get;
set;
}
public string UpdatedBy
{
get;
set;
}
public string UpdatedDate
{
get;
set;
}
public int? ResourceGroupContentId
{
get;
set;
}
public int LanguageId
{
get;
set;
}
public string GroupName
{
get;
set;
}
}
Here goes my DTO object: file ResourceGroupDTO.cs
public class ResourceGroupDTO
{
public int ResourceGroupId
{
get;
set;
}
public int? Position
{
get;
set;
}
[JsonProperty("groupname")]
[RegularExpression(Constants.GeneralStringRegularExpression)]
public string GroupName
{
get;
set;
}
}
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
// Auto Mapper Configurations
var mappingConfig = new MapperConfiguration(mc =>
{
mc.AddProfile(new MappingProfile());
}
);
IMapper mapper = mappingConfig.CreateMapper();
services.AddSingleton(mapper);
}
MappingProfile.cs
public class MappingProfile : Profile
{
public MappingProfile()
{
CreateMap<ResourceGroups, ResourceGroupDTO>();
CreateMap<List<ResourceGroups>, List<ResourceGroupDTO>>();
}
}
file ResourceGroupService.cs
public class ResourceGroupService : IResourceGroupService
{
private readonly DemoDbContext _dbContext;
private readonly ICommonService _commonService;
private readonly IMapper _mapper;
public ResourceGroupService(DemoDbContext dbContext, ICommonService commonService, IMapper mapper)
{
_dbContext = dbContext ?? throw new ArgumentNullException(nameof(dbContext));
_commonService = commonService ?? throw new ArgumentNullException(nameof(commonService));
_mapper = mapper ?? throw new ArgumentNullException(nameof(mapper));
}
public async Task<ResourceGroupDTO> GetResourceGroupDetailsAsync(int resourceGroupId, int languageId)
{
var resourceGroup = await _dbContext.ResourceGroups.Where(rg => rg.ResourceGroupId.Equals(resourceGroupId) && rg.IsPublished.Equals(true))
.Select(rg => new { rg.ResourceGroupId, rg.Position, rg.GroupName, rg.LanguageId })
.AsNoTracking().ToListAsync();
var resGroup = resourceGroup.FirstOrDefault(rg => rg.LanguageId.Equals(languageId));
return _mapper.Map<ResourceGroupDTO>(resGroup);
}
}
While debugging the above code I get the below error:
Missing type map configuration or unsupported mapping. \n \nMapping types : \
n<> f__AnonymousType4 ` 4 ->
ResourceGroupDTO \n<> f__AnonymousType4 ` 4
[
[System.Int32, System.Private.CoreLib, Version = 4.0 .0 .0 , Culture = neutral, PublicKeyToken = 7 cec85d7bea7798e] ,
[System.Nullable ` 1[
[System.Int32, System.Private.CoreLib, Version = 4.0 .0 .0 , Culture = neutral, PublicKeyToken = 7 cec85d7bea7798e] ] ,
System.Private.CoreLib , Version = 4.0 .0 .0 , Culture = neutral , PublicKeyToken = 7 cec85d7bea7798e ] , [System.String, System.Private.CoreLib, Version = 4.0 .0 .0 , Culture = neutral, PublicKeyToken = 7 cec85d7bea7798e] ,
[System.Int32, System.Private.CoreLib, Version = 4.0 .0 .0 , Culture = neutral, PublicKeyToken = 7 cec85d7bea7798e] ] ->
Author.Query.Persistence.DTO.ResourceGroupDTO \n -- ->AutoMapper.AutoMapperMappingException : Missing type map configuration or unsupported mapping. \n \nMapping types : \
n<> f__AnonymousType4 ` 4 ->

Answer 1

You're trying to map an anonymous type, i.e.
new { rg.ResourceGroupId, rg.Position, rg.GroupName, rg.LanguageId }
onto a ResourceGroupDTO, hence the error.
To quickly fix your error you could just change the above to
new ResourceGroupDTO { ResourceGroupId = rg.ResourceGroupId, Position = rg.Position, GroupName = rg.GroupName, LanguageId = rg.LanguageId }
and then add LanguageId to ResourceGroupDTO and get rid of the mapper.
But what you should really be using is ProjectTo and you should change your .FirstOrDefault to a .Where - to make your query more efficient, in the format shown below:
await _dbContext.ResourceGroups
.AsNoTracking()
.Where(/* Put your where here */)
.ProjectTo<ResourceGroupDTO>(_mapper.Configuration)
.FirstOrDefaultAsync();
You can also simplify your startup