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Joining three tables and using a left outer join

开发者 https://www.devze.com 2023-03-08 12:47 出处:网络
I have three tables.Two of them join equally but one will need to join with a left.I\'m finding a lot of code to do this in linq but between two tables only.

I have three tables. Two of them join equally but one will need to join with a left. I'm finding a lot of code to do this in linq but between two tables only.

Here is the SQL code that I'm trying to re-code within LINQ.

   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;

Here is a snippet of LINQ code that I'm using as a base. I'm just not able to piece together the third table (product in my sample SQL) via LINQ and with a left outer join. The sample is between two tables. Than开发者_运维问答ks for any tips.

   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 };

Michael


How about this:

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 })

EDIT: if you want to do a left outer join on all tables, you can do it like this:

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 })


Taken from another Stackoverflow thread somewhere, there's a more legible way to do this:

   var loj = (from prsn in db.People
           from co in db.Companies.Where(co => co.Person_ID == prsn.Person_ID).DefaultIfEmpty()
           from prod in db.Products.Where(prod => prod.Person_ID == prsn.Person_ID).DefaultIfEmpty()
           select new { Person = prsn.NAME, Company = co.NAME, Product = prod.NAME })

This uses a mix of linq query syntax and lambda syntax to what (I believe is) the best result. There's no copious re-aliasing of identifiers, and it's the most concise way to do this that I've seen.

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