Microsoft.EntityFrameworkCore ProjectTo() 找不到我的存储库的方法定义

Question

I have just started working with databases and Entity Framework for the first time in C# and I am trying to get all the data out of my database right now but I can't seem to use the ProjectTo<T>() method in my method I am writing. It does not show up in my autocomplete on VS Studio and throws me the error

IIncludableQueryable<User, DateTime>' does not contain a definition for 'ProjectTo' and no accessible extension method 'ProjectTo' accepting a first argument of type 'IIncludableQueryable<User, DateTime>' could be found (are you missing a using directive or an assembly reference?)

So I was wondering if anyone knew how to fix this? Thanks for your help in advance

Here is my code:

UserRepository.cs:

using GraphQL.Introspection;
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace AppName.GraphQL
{
    public class UserRepository
    {
        private readonly UserDBContext userDBContext;

        public UserRepository(UserDBContext userDBContext)
        {
            this.userDBContext = userDBContext;
        }

        //GET request to get all the users from the db
        public async Task<List<T>> GetAll<T>()
        {
            return await userDBContext
                .Users
                .Include(x => x.Id)
                .Include(x => x.Username)
                .Include(x => x.Password)
                .Include(x => x.Email)
                .Include(x => x.DateOfBirth)
                .Include(x => x.DateCreated)
                .ProjectTo<T>()//throws the error
                .ToListAsync();
        }

        public async Task<IEnumerable<User>> GetAll()
        {
            return await userDBContext
                .Users
                .Include(x => x.Id)
                .Include(x => x.Username)
                .Include(x => x.Password)
                .Include(x => x.Email)
                .Include(x => x.DateOfBirth)
                .Include(x => x.DateCreated)
                .ToListAsync();
        }
    }
}

UserContext.cs

namespace AppName.GraphQL
{
    public class UserDBContext : DbContext
    {
        public static string DbConnectionString = "mongodb://localhost:27020/PetPetOnline";
        
        public UserDBContext(DbContextOptions<UserDBContext> options) : base(options) { }

        public DbSet<User> Users { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<User>().HasData(new User(ObjectId.GenerateNewId(),"Jon", "abadpassword", "jon@PetPetOnline.xyz", DateTime.ParseExact("1998-01-16 00:00:00,000", "yyyy-MM-dd HH:mm:ss,fff", System.Globalization.CultureInfo.InvariantCulture), DateTime.Now));
            base.OnModelCreating(modelBuilder);
        }
    }
} 

and User.cs

public class User
{
    [Key]
    public  ObjectId Id { get; set; }

    [Required]
    [StringLength(100)]
    public string Username { get; set; }

    [Required]
    [StringLength(200)]
    public string Password { get; set; }

    [Required]
    [StringLength(200)]
    public string Email { get; set; }

    [Required]
    public DateTime DateOfBirth { get; set; }

    public DateTime DateCreated { get; set; }

    public User(ObjectId id, string username, string password, string email, DateTime dateOfBirth, DateTime dateCreated)
    {
        Id = id;
        Username = username;
        Password = password;
        Email = email;
        DateOfBirth = dateOfBirth;
        DateCreated = dateCreated;
    }
}

Answer 1

I wanted to give some recomendations before solution.

1. You need to use the .Include() function only for navigation properties.
2. I'm not sure if you really need a generic type for function GetAll<T> (anyway I will give you a solution to check if automapper support the projection). Maybe you want to change it to UserDto type?

To start you need to install AutoMapper. You're using Asp.Net Core, then I recommend you to install the AutoMapper.Extensions.Microsoft.DependencyInjection

Install-Package AutoMapper.Extensions.Microsoft.DependencyInjection

Now you need to configure the AutoMapper. To make it simply, I will use the AutoMapAttribute but for complex mapping definitions I recommend you to use AutoMapper Profile.

[AutoMap(typeof(User))]
public class UserDto
{
    public string Username { get; set; }
    public string Email { get; set; }
    //add the other properties if you need it
}

Then go to Startup class, and register the AutoMapper configuration.

public void ConfigureServices(IServiceCollection services)
{
    services.AddAutoMapper(o => o.AddMaps(typeof(Startup).Assembly));
...

The UserRepository :

public class UserRepository
{
    private readonly UserDbContext _userDbContext;
    private readonly IMapper _mapper;

    public UserRepository(UserDbContext userDbContext, IMapper mapper)
    {
        _userDbContext = userDbContext;
        _mapper = mapper;
    }
    
    public async Task<List<T>> GetAll<T>()
    {
        var supportProjection = _mapper.ConfigurationProvider
            .GetAllTypeMaps()
            .Any(x => x.SourceType == typeof(User) && x.DestinationType == typeof(T));

        if (!supportProjection)
            throw new InvalidOperationException("Unsupported projection type");

        return await _userDbContext
            .Users
            .ProjectTo<T>(_mapper.ConfigurationProvider)
            .ToListAsync();
    }
    
    public async Task<IEnumerable<User>> GetAll()
    {
        return await _userDbContext
            .Users
            .ToListAsync();
    }
}

Answer 2

You need to add AutoMapper to your project and then add using AutoMapper; to the class in which you are using it.

Install AutoMapper from the package manager console or from Nuget Package Manager.

PM> Install-Package AutoMapper

Reference:

https://docs.automapper.org/en/stable/Queryable-Extensions.html#queryable-extensions