NHibernate Linq中的Equals方法和==运算符有什么区别？

Question

When I used the following code:

session.Query<Url>().Where(ur => ur.QueryString == url.QueryString)

I found my results, but when I tried the same with .Equals, didn't. Why? The Equals() method is the default one, no overrides.

What's the difference between these LINQ queries?

Answer 1

The biggest difference is that they are different "functions". public static bool operator == (Object other) and public bool Equals(Object other) can be independently defined.

However, even when they do the same thing (or one calls the other), the fact that they are different calls still means something to a Linq provider. The upshot is that the NHibernate queryable provider, which "translates" the expression tree you create using a Linq query or method chain, might treat the two differently. It might correctly parse .Where(ur => ur.QueryString == url.QueryString) into WHERE ur.QueryString = 'MyUrlQueryStringValue' , but .Where(ur => ur.QueryString.Equals(url.QueryString)) might be ignored as unusable, or return an error, or be parsed into WHERE 0 .

Answer 2

One would end up using 'Equals' when comparing objects...or entities.

'==' is something you will always use when comparing just values...such as strings.

Answer 3

==比较引用，而Equals()是一个虚拟方法，可以实现，但是可以实现。