IQueryable的优点 <T> IList <T>

Question

在C＃DAL中，如果我返回IQueryable而不是IList，我将获得什么样的优势，Iam没有使用Entity Framework / N Hibernate，只是普通的旧ADO.Net ..

Answer 1

I believe returning an IQueryable allows lazy enumeration, whilst returning an IList doesn't.

If you return an IList, the query against the database is performed at the point the DAL returns the IList. Returning an IQueryable, the return can be passed around and the query is only executated when you inspect the contents of the IQueryable.

(This is based on my experience of LINQ to SQL - but I've not checked this against a definitive source)

Answer 2

You can keep querying against IQueryable. IQueryable is not for your final return type but good for private helpers which build on original queries - reusable, composable pieces of queries that have an expected return type of the underlying type in your IQueryable<>.

Answer 3

You should return an IEnumerable instead of IList or IQueryable:

IQueryable makes the caller think they can use lazy evaluation and add filters, sorting, projection, etc.

IList allows the caller to add, remove, reverse, set values, and otherwise modify the returned collection. This might not be a problem for you, but if you plan on sharing data between calls then you need to watch out for this

IEnumerable provides the caller an immutable collection which they know doesn't not support lazy evaluation.