求下述LINQ查询表达式对应的Lambda表达式等价写法

Hey there! Let's convert that LINQ query syntax into its equivalent Lambda expression. Here's the direct translation that matches the logic of your original query:

var e = postList.SelectMany(
    p => authorList.Where(a => p.AuthorId == a.Id),
    (p, a) => new { p, a }
);

Quick Breakdown: #

• SelectMany handles the nested from clauses (this is what enables the cross join behavior between postList and authorList).
• The first parameter to SelectMany filters the authorList for each post, only keeping authors where their Id matches the post's AuthorId.
• The second parameter projects the matching post-author pairs into the same anonymous type your original query uses.

If you prefer a more verbose (but functionally equivalent) version that mirrors the "filter after joining" structure of your original query, you could also write it like this:

var e = postList
    .SelectMany(p => authorList, (p, a) => new { p, a })
    .Where(x => x.p.AuthorId == x.a.Id);

Just note that the first version is more efficient because it filters the author list before combining it with each post, rather than creating a full Cartesian product first and then filtering.

内容的提问来源于stack exchange，提问作者Everton Santos