c# - 使用包含检索实体的通用存储库和 Entity Framework 逻辑

Question

我有两个 Entity Framework 5执行 (i) 单个实体的 Get() 方法通过 ID 获取，(ii) 单个实体通过过滤器获取，并附加任何预加载。代码见下:

internal readonly FallenNovaContext Context;
private readonly DbSet<TEntity> _dbSet;

internal GenericRepository(FallenNovaContext context)
{
    Context = context;
    _dbSet = context.Set<TEntity>();
}

// (i) Get by ID.
public TEntity GetById(int id)
{
    return _dbSet.Find(id);
}

// (ii) Get by filter and optional eager loading includes.
public TEntity Get(
    Expression<Func<TEntity, bool>> filter = null,
    IEnumerable<string> includePaths = null)
{
    IQueryable<TEntity> query = _dbSet;

    if (filter != null)
    {
        query = query.Where(filter);
    }

    if (includePaths != null)
    {
        query = includePaths.Aggregate(query, (current, includePath) => current.Include(includePath));
    }

    return query.SingleOrDefault();
}

现在所有这些都工作正常，随着我的应用程序的增长，我发现我正在编写很多需要两者混合的非泛型方法——更具体地说，我想要一个通过 ID 获取的泛型，并且还能够急切加载相关实体。

所以方法签名看起来像这样:

 public TEntity GetById(
     int id,
     IEnumerable<string> includePaths)
 {
       // ???
 }

我可以这样调用它:

 User user = UnitOfWork.UserRepository.GetById(117, new List<string>() { "UserRole", "UserStatus" });

或者像这样:

 Car car = UnitOfWork.CarRepository.GetById(51, new List<string>() { "Make", "Model", "Tyres" });

任何有关我如何使用 Entity Framework 5 为 TEntity GetById(int id, IEnumerable includePaths) 方法编写逻辑的建议的帮助将不胜感激。

Answer 1

首先，为实体写一个基类，定义主键字段。像下面这样的东西可能会起作用:

public abstract class BaseEntity
{
    public int Id {get;set;}
}

然后，为您的存储库编写一个基类；在此基础存储库中定义所有通用方法。让这个存储库有一个实体类型的通用参数:

public class RepositoryBase<TEntity> where TEntity : BaseEntity
{
   public TEntity GetById(
     int id,
     params Expression<Func<TEntity, object>>[] includeList)
     {
            TEntity entity = null;
            ObjectQuery<TEntity> itemWithIncludes = context.Set<TEntity>() as ObjectQuery<TEntity>;
            foreach (Expression<Func<TEntity, object>> path in includeList)
            {
                itemWithIncludes = ((IQueryable)itemWithIncludes.Include(path)) as ObjectQuery<T>;
            }

            IQueryable<TEntity> items = itemWithIncludes.AsQueryable<TEntity>();
            entity = items.Where(p => p.Id == id).SingleOrDefault();
            return entity;
     }
}

更新:@Bern 询问除了声明基类之外是否还有其他方法可以找到主键。以下问题均涉及此问题。

Entity Framework 4: How to find the primary key?

Entity Framework code first. Find primary key

另一方面，我不知道 EF 5 中是否还有其他方法。