1

我正在尝试使用实体框架中的通用存储库,并遇到以下代码:

public class GenericRepository<TContext, TEntity> : IGenericRepository<TEntity>
where TContext : IUnitOfWork
where TEntity : class
{
protected TContext _context;
/// <summary>
/// Constructor that takes a context
/// </summary>
/// <param name="context">An established data context</param>
public GenericRepository(TContext context)
{
    _context = context;
}

public IQueryable<TEntity> Select()
{
    return _context.Set<TEntity>().AsQueryable();
}

public IEnumerable<TEntity> GetAll()
{
    return _context.Set<TEntity>().AsEnumerable();
}

public IEnumerable<TEntity> Where(Func<TEntity, bool> predicate)
{
    return _context.Set<TEntity>().Where(predicate);
}

public TEntity GetSingle(Func<TEntity, bool> predicate)
{
    return _context.Set<TEntity>().Single(predicate);
}

public TEntity GetFirst(Func<TEntity, bool> predicate)
{
    return _context.Set<TEntity>().First(predicate);
}

public void Add(TEntity entity)
{
    if (entity == null)
        throw new ArgumentException("Cannot add a null entity");

    _context.Set<TEntity>().Add(entity);
}

public void Delete(TEntity entity)
{
    if (entity == null)
        throw new ArgumentException("Cannot delete a null entity");

    _context.Set<TEntity>().Remove(entity);
}

public void Attach(TEntity entity)
{
    if (entity == null)
        throw new ArgumentException("Cannot attach a null entity");

    _context.Set<TEntity>().Attach(entity);
}

#region IDisposable implementation
private bool disposedValue;

public void Dispose(bool disposing)
{
    if (!this.disposedValue)
    {
        if (disposing)
        {
            // dispose managed state here if required
        }
        // dispose unmanaged objects and set large fields to null
    }
    this.disposedValue = true;
}

public void Dispose()
{
    Dispose(true);
    GC.SuppressFinalize(this);
}
#endregion
 }

但是我发现有点难以理解对创建的构造函数的需求

/// <summary>
/// Constructor that takes a context
/// </summary>
/// <param name="context">An established data context</param>
public GenericRepository(TContext context)
{
    _context = context;
}

有人可以解释一下这个的用途吗?

谢谢

4

1 回答 1

2

那是因为你的项目中可能有多个 DbContext 类,所以你需要注入一个特定的 DbContext 实例来告诉 GenericRepository 类你正在使用哪个 DbContext。

您需要拥有多个 DbContext 类的原因可能是:

  1. 您的项目针对多个数据库;

  2. 您的项目很大,出于性能和可维护性的考虑,您希望将其拆分为几个模块。例如:

    public class BaseContext<TContext> : DbContext
      where TContext : DbContext, new()        
    {        
        protected BaseContext()
        : base("name=ConnectionString")
        {            
        }
    }
    
    public class ShopDbContext :BaseContext<ShopDbContext>
    {
        public DbSet<Product> Products{ get; set; }
    }
    
    public class BlogDbContext :BaseContext<BlogDbContext>
    {
        public DbSet<Blog> Blogs{ get; set; }
    }
    

现在,如果要查询 Products,则必须实例化 ShopDbContext,并将其传递给 GenericRepository 构造函数(IoC 是一个不错的选择)。

于 2012-10-31T06:32:44.827 回答