注入泛型仓储后EF Core中Include方法失效问题排查与解决

问题背景 #

我一直采用「创建DB上下文 + 实现泛型仓储」的模式开发，泛型仓储实现代码如下：

public class GenericRepository<T> : IGenericRepository<T>
 where T : BaseDomain
 {
     private readonly FitnessAppContext _dbContext;

     public GenericRepository(FitnessAppContext dbContext)
     {
         _dbContext = dbContext;
     }

     public async Task Create(T entity)
     {
         await _dbContext.AddAsync(entity);
         _dbContext.SaveChanges();
     }

     public async Task Delete(Guid id)
     {
         _dbContext.Set<T>().FirstOrDefault(a => a.Id.Equals(id)).Delete();
         _dbContext.SaveChanges();
     }

     public IQueryable<T> GetAll()
     {
         return _dbContext.Set<T>().Where(a => a.IsDeleted.Equals(false)).AsQueryable();
     }

     public async Task<T> GetById(Guid id)
     {
         var entity = await _dbContext.Set<T>().FirstOrDefaultAsync(a => a.Id.Equals(id) && a.IsDeleted.Equals(false));
         return entity;
     }

     public async Task Update(T entity)
     {
         _dbContext.Set<T>().Update(entity);
         await _dbContext.SaveChangesAsync();
     }

     public async Task<DbSet<T>> GetSet()
     {
         return _dbContext.Set<T>();
     }

     public IQueryable<T> GetByFilter(Expression<Func<T, bool>> predicate)
     {
         return _dbContext.Set<T>().Where(predicate).AsQueryable().Where(a=>a.IsDeleted.Equals(false)).AsQueryable();
     }

     public async Task ModifyAndSave()
     {
         await _dbContext.SaveChangesAsync();
     }
}

依赖注入的代码如下：

private readonly IGenericRepository<Customer> _customerGenericRepository;
private readonly IGenericRepository<Training> _trainingGenericRepository;
public FitnessAppQuery(IGenericRepository<Customer> customerGenericRepository,
    IGenericRepository<Training> trainingGenericRepository)
{
    _customerGenericRepository = customerGenericRepository;
    _trainingGenericRepository = trainingGenericRepository;
}

Program.cs中的服务注册配置：

builder.Services.AddDbContext<FitnessAppContext>();
builder.Services.AddTransient<ITrainingService, TrainingService>();
builder.Services.AddScoped(typeof(IGenericRepository<>), typeof(GenericRepository<>));
builder.Services.AddScoped<IFitnessAppQuery, FitnessAppQuery>();
builder.Services.AddMediatR(cfg => cfg.RegisterServicesFromAssembly(Assembly.GetExecutingAssembly()));

遇到的问题 #

在业务逻辑层调用仓储的GetSet()方法，尝试通过.Include()加载关联对象TrainingType时，主数据能正常获取，但关联对象始终为null：

public async Task<ListTrainingOutputModel> ListAllTraining()
{
     var outputModel = new ListTrainingOutputModel();
     var trainingSet = await _trainingGenericRepository.GetSet();
     var trainingswithincluded = trainingSet.Include(a => a.TrainingType).ToList();

     try
     {
         outputModel.IsSuccess = true;
         outputModel.StatusMessage = "Trainings listed successfully";
         return outputModel;
     }
     catch (Exception ex)
     {
         outputModel.Data = null;
         outputModel.IsSuccess = false;
         outputModel.StatusMessage = ex.ToString();
         return outputModel;
     }
}

查阅大量文档和工具后仍未解决，最终定位到问题根源。

解决方法 #

问题出在Include方法的命名空间引用错误：我误用了Microsoft.System.Data中的Include()方法，而EF Core中用于加载关联对象的正确方法来自Microsoft.EntityFrameworkCore命名空间。替换引用的命名空间后，关联对象正常加载，问题解决。

内容的提问来源于stack exchange，提问作者gokaydinc