linq - 连接三个表并使用左外连接

Question

我有三张 table 。他们中的两个平等地加入，但一个需要左翼加入。我在 linq 中找到了很多代码来执行此操作，但仅在两个表之间。

这是我试图在 LINQ 中重新编码的 SQL 代码。

   SELECT PRSN.NAME
       ,CO.NAME
       ,PROD.NAME
   FROM PERSON PRSN
     INNER JOIN COMPANY CO ON PRSN.PERSON_ID = CO.PERSON_ID
     LEFT OUTER JOIN PRODUCT PROD ON PROD.PERSON_ID = PROD.PERSON_ID;

这是我用作基础的 LINQ 代码片段。我只是无法通过 LINQ 和左外连接拼凑第三个表(我的示例 SQL 中的产品)。样本位于两个表之间。感谢您的任何提示。

   var leftOuterJoinQuery =
    from category in categories
    join prod in products on category.ID equals prod.CategoryID into prodGroup
    from item in prodGroup.DefaultIfEmpty(new Product{Name = String.Empty, CategoryID = 0})
        select new { CatName = category.Name, ProdName = item.Name };

迈克尔

Answer 1

这个怎么样:

var loj = (from prsn in db.People
           join co in db.Companies on prsn.Person_ID equals co.Person_ID
           join prod in db.Products on prsn.Person_ID equals prod.Person_ID into prods
           from x in prods.DefaultIfEmpty()
           select new { Person = prsn.NAME, Company = co.NAME, Product = x.NAME })

编辑:如果你想对所有表进行左外连接，你可以这样做:

var loj = (from prsn in db.People
           join co in db.Companies on prsn.Person_ID equals co.Person_ID into comps
           from y in comps.DefaultIfEmpty()
           join prod in db.Products on prsn.Person_ID equals prod.Person_ID into prods
           from x in prods.DefaultIfEmpty()
           select new { Person = prsn.NAME, Company = y.NAME, Product = x.NAME })