我遇到了用LINQ和Lambda编写的查询的麻烦。到目前为止,我的代码很多:
int id = 1; var query = database.Posts.Join(database.Post_Metas, post => database.Posts.Where(x => x.ID == id), meta => database.Post_Metas.Where(x => x.Post_ID == id), (post, meta) => new { Post = post, Meta = meta });
我是使用LINQ的新手,所以不确定此查询是否正确。
我发现,如果您熟悉SQL语法,则使用LINQ查询语法会更清晰,更自然,并且更容易发现错误:
var id = 1; var query = from post in database.Posts join meta in database.Post_Metas on post.ID equals meta.Post_ID where post.ID == id select new { Post = post, Meta = meta };
但是,如果您真的很喜欢使用lambda,那么您的语法就会有些偏离。这是使用LINQ扩展方法的相同查询:
var id = 1; var query = database.Posts // your starting point - table in the "from" statement .Join(database.Post_Metas, // the source table of the inner join post => post.ID, // Select the primary key (the first part of the "on" clause in an sql "join" statement) meta => meta.Post_ID, // Select the foreign key (the second part of the "on" clause) (post, meta) => new { Post = post, Meta = meta }) // selection .Where(postAndMeta => postAndMeta.Post.ID == id); // where statement