EF4：如何使用一个通用存储库的模式？ [英] EF4: how to use a generic repository pattern ?

问题描述

我试图用通用的回购我可以从子类来简化现有的回购协议。问题是，我无法弄清楚如何写我的几个基类的方法。我目前有：

I'm trying to streamline my existing repos by using a generic repo I can subclass from. The problem is that I can't figure out how to write a few of my base class methods. I currently have:

public interface IRepository<T> : IDisposable where T : class
{
    IQueryable<T> GetAll();
    T GetSingle(int id);
    T GetSingle(string slug);
    void Save(T entity);
}

public class HGRepository<T> : IRepository<T> where T : class
{
    protected HGEntities _siteDB;
    protected IObjectSet<T> _objectSet;

    public HGRepository(HGEntities context)
    {
        _siteDB = context;
        _objectSet = _siteDB.CreateObjectSet<T>();
    }

    public IQueryable<T> GetAll()
    {
        return _objectSet;
    }

    public T GetSingle(int id)
    {
        return null;
    }

    public T GetSingle(string slug)
    {
        return null;
    }

    public void Save(T entity)
    {
        // code to save entity
    }

    public void Dispose()
    {
        _siteDB = null;
    }
}

我的困惑在于我的 GetSingle（）和保存（）方法。他们将需要依靠这与每种类型 T 的信息稍有不同。从我的非通用回购例如：

My confusion lies with my GetSingle() and Save() methods. They'll need to rely on information that's slightly different with each type of T. Example from my non-generic repos:

public Article GetArticle(int id)
{
    return _siteDB.Articles.SingleOrDefault(a => a.ArticleID == id);
}

public Article GetArticle(string slug)
{
    return _siteDB.Articles.SingleOrDefault(a => a.Slug == slug);
}

public void SaveArticle(Article article)
{
    if (article.ArticleID > 0)
    {
        _siteDB.ObjectStateManager.ChangeObjectState(article, System.Data.EntityState.Modified);
    }
    else
    {
        _siteDB.Articles.AddObject(article);
    }

    _siteDB.SaveChanges();
}

正如你所看到的，文章有自己的，特定的ID。我的其他实体同样的事情（新闻项目有一个NewSID的属性，例如）。

As you can see, Articles have their own, specific id. The same thing for my other entities (News items have a NewsID property, for instance).

我怎么能作出这样可以调和成一个更具体的版本，一个抽象基方法是什么？

How can I make an abstract base method that can be reconciled into a more specific version?

推荐答案

您可以有一个通用的前pression 您 GetSingle 方法的参数：

You can have a generic expression parameter for your GetSingle method:

public interface IRepository<T> : IDisposable where T : class
{
    ....
    T GetSingle(Expression<Func<T, bool>> filter);
    void Save(T entity);
}

和 HGRepository＆LT; T＆GT; ：

public T GetSingle(Expression<Func<T, bool>> filter)
{
        return _objectSet.Where(filter).SingleOrDefault();
}

和用法：

IRepository<Article> rep = new HGRepository<Article>();
return rep.GetSingle(p => p.Slug == slug);

如果您有特殊的情况下该通用接口/ repository类不包括，你可以创建新的接口/类从一般的人继承：

If you have particular scenarios which the generic interface / repository class don't cover, you can create new interface / class which inherit from the generic ones:

public interface IArticleRepository : IRepository<Article>
{
   ...
}

public class ArticleRepository : HGRepository<Article>, IArticleRepository
{
   ...
}

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