c# - 如何将此 T-SQL 语句转换为 linq

Question

我是 linq 初学者，我已经写了这个 T-SQL 查询

select * from DOCUMENT_TYPES where document_id in(
select document_id from Clearance_Document where Clearance_id=(select clearance_id from clearance_id from request where request_id=3)) 

我想将此 T-SQL 查询转换为 linq，请帮助我，谢谢

Answer 1

好吧，我会首先将您的 SQL 重构为嵌套子查询链以外的东西。我认为这应该做同样的事情，而且它更具可读性:

SELECT
    *
FROM
    DOCUMENT_TYPES dt
JOIN
    Clearance_Document cd
    ON
    dt.document_id = cd.document_id
JOIN
    Request r
    ON
    cd.clearance_id = r.clearance_id
WHERE 
    r.request_id = 3

(我假设 from clearance_id from request 是一个拼写错误。)

然后您可以轻松重构为 LINQ 语句:

var result = from dt in DOCUMENT_TYPES
             join cd in Clearance_Document on dt.document_id equals cd.document_id
             join r in Request on cd.clearance_id equals r.clearance_id
             where r.request_id = 3
             select new {
                property1 = dt.something,
                property2 = cd.somethingElse,
                ...
             };