我应该返回 IEnumerable<T>或 IQueryable<T>从我的 DAL? [英] Should I return IEnumerable<T> or IQueryable<T> from my DAL?
问题描述
我知道这可能是意见，但我正在寻找最佳做法.
I know this could be opinion, but I'm looking for best practices.
据我所知，IQueryable 实现了 IEnumerable，所以在我的 DAL 中，我目前有如下方法签名:
As I understand, IQueryable<T> implements IEnumerable<T>, so in my DAL, I currently have method signatures like the following:
IEnumerable<Product> GetProducts();
IEnumerable<Product> GetProductsByCategory(int cateogoryId);
Product GetProduct(int productId);
我应该在这里使用 IQueryable 吗?
Should I be using IQueryable<T> here?
这两种方法的优缺点是什么?
What are the pros and cons of either approach?
请注意，我计划使用 Repository 模式，因此我将拥有一个这样的类:
Note that I am planning on using the Repository pattern so I will have a class like so:
public class ProductRepository {
DBDataContext db = new DBDataContext(<!-- connection string -->);
public IEnumerable<Product> GetProductsNew(int daysOld) {
return db.GetProducts()
.Where(p => p.AddedDateTime > DateTime.Now.AddDays(-daysOld ));
}
}
我应该将 IEnumerable 更改为 IQueryable 吗?两者有什么优点/缺点?
Should I change my IEnumerable<T> to IQueryable<T>? What advantages/disadvantages are there to one or the other?
推荐答案
这取决于你想要什么样的行为.
It depends on what behavior you want.
- 返回一个 IList
告诉调用者他们已经收到了他们请求的所有数据 - 返回一个 IEnumerable
告诉调用者他们需要迭代结果并且它可能被延迟加载. - 返回一个 IQueryable
告诉调用者结果由可以处理某些类查询的 Linq 提供程序提供支持，从而将负担交给调用者以形成高性能查询.莉>
- Returning an IList<T> tells the caller that they've received all of the data they've requested
- Returning an IEnumerable<T> tells the caller that they'll need to iterate over the result and it might be lazily loaded.
- Returning an IQueryable<T> tells the caller that the result is backed by a Linq provider that can handle certain classes of queries, putting the burden on the caller to form a performant query.
虽然后者为调用者提供了很大的灵活性(假设您的存储库完全支持它)，但它最难测试，而且可以说是最不具有确定性的.
While the latter gives the caller a lot of flexibility (assuming your repository fully supports it), it's the hardest to test and, arguably, the least deterministic.
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