为什么Dbset已经实现IQueryable时实现了IEnumerable？

Question

当Dbset已经具有IQueryable时，它似乎实现了IEnumerable，但这并不会使IEnum的实现成为多余，因为IQueryable已经实现了IEnum。

Answer 1

First of all, we should correct your terminology:

IQueryable already implements IEnum.

IQueryable doesn't implement anything. It inherits IEnum , which means that every class that implements IQueryable must implement the members of IEnum as well as the members of IQueryable .

I think your question actually is this: why is DbSet defined as implementing IEnum , when it implements IQueryable so it has to implement IEnum anyway.

Technically, stating that DbSet implements IEnum is redundant.

Which leaves the question, Why would anyone unnecessarily state a base interface?

I'll quote this blog article by Eric Lippert: https://blogs.msdn.microsoft.com/ericlippert/2011/04/04/so-many-interfaces/

Perhaps because they believe that doing so makes the code easier to understand and more self-documenting.

Or, perhaps the developer wrote the code as

interface I1 {}

interface I2 {}

interface I3 : I1, I2 {}

and the realized, oh, wait a minute, I2 should inherit from I1. Why should making that edit then require the developer to go back and change the declaration of I3 to not contain explicit mention of I1? I see no reason to force developers to remove redundant information.

Answer 2

Sometimes you need all rows of a specific table without any additional where clause, in IEnumerable format. in these circumstances, you can directly cast the DbSet to IEnumerable .