Linq —如何在ForEach语句中执行Join？

Question

The Linq Join examples I've seen illustrate hot ti Join when creating an anonymous type. How do I do the the Join in a ForEach statement.

eg

foreach (item i in MyContext.SomeEntity.Include("NavigationProperty1").Include("NavigationProperty2").Join(MyContext.SomeEntity2 on id == id)
{
}

Thanks!

Answer 1

Well, you're trying to mix query syntax with just calling the extension methods directly here - that's not going to work to start with.

But the result of a join is a sequence of pairs , effectively - pairs which have some property in common. It's not clear where "item" comes from - how do you want each pair from SomeEntity and SomeEntity2 to be transformed into an item ?

Your call is likely to end up looking something like:

...Join(MyContext.SomeEntity2, x => x.id, y => y.id, (x, y) => !!!)

where the !!! is the projection from a pair of entities to a single useful value.

See part 19 of my Edulinq blog series for more information about how the Join method works.