blocks|key|3112896|text|你所看到的就是你所得到的--这正是你所要求的，这里：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3112897|(ppc,+c)+=>+new+{+productproductcategory+=+ppc,+category+=+c}|code-block|syntax|javascript|3112898|这是一个返回具有这两个属性的匿名类型的lambda表达式。|3112899|在你的CategorizedProducts中，你只需要遍历这些属性：|3112900|CategorizedProducts+catProducts+=+query.Select(
++++++m+=>+new+{+
+++++++++++++ProdId+=+m.productproductcategory.product.Id,+
+++++++++++++CatId+=+m.category.CatId,+
+++++++++++++//+other+assignments+
+++++++++++});|3112901|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

What you've seen is what you get - and it's exactly what you asked for, here:

<pre><code>(ppc, c) =&gt; new { productproductcategory = ppc, category = c}
</code></pre>

That's a lambda expression returning an anonymous type with those two properties.

In your CategorizedProducts, you just need to go via those properties:

<pre><code>CategorizedProducts catProducts = query.Select(
 m =&gt; new { 
 ProdId = m.productproductcategory.product.Id, 
 CatId = m.category.CatId, 
 // other assignments 
 });
</code></pre>

blocks|key|2898717|text|对于连接，我强烈倾向于查询语法，因为所有细节都隐藏得很好(其中最重要的是中间投影所涉及的透明标识符，这些标识符在点语法等效项中很明显)。然而，你问到了Lambdas，我认为你已经拥有了你需要的一切-你只需要把它们放在一起即可。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2898718|var+categorizedProducts+=+product
++++.Join(productcategory,+p+=>+p.Id,+pc+=>+pc.ProdId,+(p,+pc)+=>+new+{+p,+pc+})
++++.Join(category,+ppc+=>+ppc.pc.CatId,+c+=>+c.Id,+(ppc,+c)+=>+new+{+ppc,+c+})
++++.Select(m+=>+new+{+
++++++++ProdId+=+m.ppc.p.Id,+//+or+m.ppc.pc.ProdId
++++++++CatId+=+m.c.CatId
++++++++//+other+assignments
++++});|code-block|syntax|javascript|2898719|如果需要，您可以将连接保存到局部变量中并在以后重用它，尽管缺少其他相反的细节，我认为没有理由引入局部变量。|2898720|此外，您可以将Select抛入第二个Join的最后一个lambda中(同样，假设没有其他依赖于连接结果的操作)，这将提供：|offset|length|style|CODE|2898721|var+categorizedProducts+=+product
++++.Join(productcategory,+p+=>+p.Id,+pc+=>+pc.ProdId,+(p,+pc)+=>+new+{+p,+pc+})
++++.Join(category,+ppc+=>+ppc.pc.CatId,+c+=>+c.Id,+(ppc,+c)+=>+new+{
++++++++ProdId+=+ppc.p.Id,+//+or+ppc.pc.ProdId
++++++++CatId+=+c.CatId
++++++++//+other+assignments
++++});|2898722|...and最后一次尝试向您推销查询语法，如下所示：|2898723|var+categorizedProducts+=
++++from+p+in+product
++++join+pc+in+productcategory+on+p.Id+equals+pc.ProdId
++++join+c+in+category+on+pc.CatId+equals+c.Id
++++select+new+{
++++++++ProdId+=+p.Id,+//+or+pc.ProdId
++++++++CatId+=+c.CatId
++++++++//+other+assignments
++++};|2898724|对于查询语法是否可用，您可能束手无策。我知道有些商店有这样的要求--通常是基于查询语法比点语法更有限的概念。还有其他原因，比如“如果我可以用点语法做更多的事情，为什么还要学习第二个语法呢？”正如这最后一部分所显示的-查询语法隐藏了一些细节，这使得它值得接受它带来的可读性改进:幸运的是，您必须准备的所有中间投影和标识符在查询语法版本中都不是最重要的-它们是背景毛绒。现在离开我的肥皂盒--不管怎样，谢谢你的问题。:)|2898725|entityMap^0|0|0|0|7|6|I|4|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|11|8|@$K|12|L|13|M|N]|$K|14|L|15|M|N]]|9|@]|A|$]]|$1|O|3|P|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|17|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|18|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|19|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|X|$]]

For joins, I strongly prefer query-syntax for all the details that are happily hidden (not the least of which are the transparent identifiers involved with the intermediate projections along the way that are apparent in the dot-syntax equivalent). However, you asked regarding Lambdas which I think you have everything you need - you just need to put it all together.

<pre><code>var categorizedProducts = product
 .Join(productcategory, p =&gt; p.Id, pc =&gt; pc.ProdId, (p, pc) =&gt; new { p, pc })
 .Join(category, ppc =&gt; ppc.pc.CatId, c =&gt; c.Id, (ppc, c) =&gt; new { ppc, c })
 .Select(m =&gt; new { 
 ProdId = m.ppc.p.Id, // or m.ppc.pc.ProdId
 CatId = m.c.CatId
 // other assignments
 });
</code></pre>

If you need to, you can save the join into a local variable and reuse it later, however lacking other details to the contrary, I see no reason to introduce the local variable.

Also, you could throw the <code>Select</code> into the last lambda of the second <code>Join</code> (again, provided there are no other operations that depend on the join results) which would give:

<pre><code>var categorizedProducts = product
 .Join(productcategory, p =&gt; p.Id, pc =&gt; pc.ProdId, (p, pc) =&gt; new { p, pc })
 .Join(category, ppc =&gt; ppc.pc.CatId, c =&gt; c.Id, (ppc, c) =&gt; new {
 ProdId = ppc.p.Id, // or ppc.pc.ProdId
 CatId = c.CatId
 // other assignments
 });
</code></pre>

...and making a last attempt to sell you on query syntax, this would look like this:

<pre><code>var categorizedProducts =
 from p in product
 join pc in productcategory on p.Id equals pc.ProdId
 join c in category on pc.CatId equals c.Id
 select new {
 ProdId = p.Id, // or pc.ProdId
 CatId = c.CatId
 // other assignments
 };
</code></pre>

Your hands may be tied on whether query-syntax is available. I know some shops have such mandates - often based on the notion that query-syntax is somewhat more limited than dot-syntax. There are other reasons, like "why should I learn a second syntax if I can do everything and more in dot-syntax?" As this last part shows - there are details that query-syntax hides that can make it well worth embracing with the improvement to readability it brings: all those intermediate projections and identifiers you have to cook-up are happily not front-and-center-stage in the query-syntax version - they are background fluff. Off my soap-box now - anyhow, thanks for the question. :)

blocks|key|235095|text|看看我的项目中的示例代码|type|unstyled|depth|inlineStyleRanges|entityRanges|data|235096|public+static+IList<Letter>+GetDepartmentLettersLinq(int+departmentId)
{
++++IEnumerable<Letter>+allDepartmentLetters+=
++++++++from+allLetter+in+LetterService.GetAllLetters()
++++++++join+allUser+in+UserService.GetAllUsers()+on+allLetter.EmployeeID+equals+allUser.ID+into+usersGroup
++++++++from+user+in+usersGroup.DefaultIfEmpty()//+here+is+the+tricky+part
++++++++join+allDepartment+in+DepartmentService.GetAllDepartments()+on+user.DepartmentID+equals+allDepartment.ID
++++++++where+allDepartment.ID+==+departmentId
++++++++select+allLetter;

++++return+allDepartmentLetters.ToArray();
}|code-block|syntax|javascript|235097|在这段代码中，我连接了3个表，并从where子句中插入了连接条件|235098|注意:服务类只是扭曲(封装)数据库操作|235099|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

take look at this sample code from my project

<pre><code>public static IList&lt;Letter&gt; GetDepartmentLettersLinq(int departmentId)
{
 IEnumerable&lt;Letter&gt; allDepartmentLetters =
 from allLetter in LetterService.GetAllLetters()
 join allUser in UserService.GetAllUsers() on allLetter.EmployeeID equals allUser.ID into usersGroup
 from user in usersGroup.DefaultIfEmpty()// here is the tricky part
 join allDepartment in DepartmentService.GetAllDepartments() on user.DepartmentID equals allDepartment.ID
 where allDepartment.ID == departmentId
 select allLetter;

 return allDepartmentLetters.ToArray();
}
</code></pre>

in this code I joined 3 tables and I spited join condition from where clause 

note: the Services classes are just warped(encapsulate) the database operations

blocks|key|237861|text|+public+ActionResult+Index()
++++{
++++++++List<CustomerOrder_Result>+obj+=+new+List<CustomerOrder_Result>();

+++++++var++orderlist+=+(from+a+in+db.OrderMasters
+++++++++++++++++++++++++join+b+in+db.Customers+on+a.CustomerId+equals+b.Id
+++++++++++++++++++++++++join+c+in+db.CustomerAddresses+on+b.Id+equals+c.CustomerId
+++++++++++++++++++++++++where+a.Status+==+"Pending"
+++++++++++++++++++++++++select+new
+++++++++++++++++++++++++{
+++++++++++++++++++++++++++++Customername+=+b.Customername,
+++++++++++++++++++++++++++++Phone+=+b.Phone,
+++++++++++++++++++++++++++++OrderId+=+a.OrderId,
+++++++++++++++++++++++++++++OrderDate+=+a.OrderDate,
+++++++++++++++++++++++++++++NoOfItems+=+a.NoOfItems,
+++++++++++++++++++++++++++++Order_amt+=+a.Order_amt,
+++++++++++++++++++++++++++++dis_amt+=+a.Dis_amt,
+++++++++++++++++++++++++++++net_amt+=+a.Net_amt,
+++++++++++++++++++++++++++++status=a.Status,++
+++++++++++++++++++++++++++++address+=+c.address,
+++++++++++++++++++++++++++++City+=+c.City,
+++++++++++++++++++++++++++++State+=+c.State,
+++++++++++++++++++++++++++++Pin+=+c.Pin

+++++++++++++++++++++++++})+;
+++++++foreach+(var+item+in+orderlist)
+++++++{

+++++++++++CustomerOrder_Result+clr+=+new+CustomerOrder_Result();
+++++++++++clr.Customername=item.Customername;
+++++++++++clr.Phone+=+item.Phone;
+++++++++++clr.OrderId+=+item.OrderId;
+++++++++++clr.OrderDate+=+item.OrderDate;
+++++++++++clr.NoOfItems+=+item.NoOfItems;
+++++++++++clr.Order_amt+=+item.Order_amt;
+++++++++++clr.net_amt+=+item.net_amt;
+++++++++++clr.address+=+item.address;
+++++++++++clr.City+=+item.City;
+++++++++++clr.State+=+item.State;
+++++++++++clr.Pin+=+item.Pin;
+++++++++++clr.status+=+item.status;

+++++++++++obj.Add(clr);



+++++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|237862|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code> public ActionResult Index()
 {
 List&lt;CustomerOrder_Result&gt; obj = new List&lt;CustomerOrder_Result&gt;();

 var orderlist = (from a in db.OrderMasters
 join b in db.Customers on a.CustomerId equals b.Id
 join c in db.CustomerAddresses on b.Id equals c.CustomerId
 where a.Status == "Pending"
 select new
 {
 Customername = b.Customername,
 Phone = b.Phone,
 OrderId = a.OrderId,
 OrderDate = a.OrderDate,
 NoOfItems = a.NoOfItems,
 Order_amt = a.Order_amt,
 dis_amt = a.Dis_amt,
 net_amt = a.Net_amt,
 status=a.Status, 
 address = c.address,
 City = c.City,
 State = c.State,
 Pin = c.Pin

 }) ;
 foreach (var item in orderlist)
 {

 CustomerOrder_Result clr = new CustomerOrder_Result();
 clr.Customername=item.Customername;
 clr.Phone = item.Phone;
 clr.OrderId = item.OrderId;
 clr.OrderDate = item.OrderDate;
 clr.NoOfItems = item.NoOfItems;
 clr.Order_amt = item.Order_amt;
 clr.net_amt = item.net_amt;
 clr.address = item.address;
 clr.City = item.City;
 clr.State = item.State;
 clr.Pin = item.Pin;
 clr.status = item.status;

 obj.Add(clr);



 }
</code></pre>

blocks|key|236243|text|var+query+=+from+a+in+d.tbl_Usuarios
++++++++++++++++++++from+b+in+d.tblComidaPreferidas
++++++++++++++++++++from+c+in+d.tblLugarNacimientoes
++++++++++++++++++++select+new
++++++++++++++++++++{
++++++++++++++++++++++++_nombre+=+a.Nombre,
++++++++++++++++++++++++_comida+=+b.ComidaPreferida,
++++++++++++++++++++++++_lNacimiento+=+c.Ciudad
++++++++++++++++++++};
++++++++foreach+(var+i+in+query)
++++++++{
++++++++++++Console.WriteLine($"{i._nombre+}+le+gusta+{i._comida}+y+nació+en+{i._lNacimiento}");
++++++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|236244|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>var query = from a in d.tbl_Usuarios
 from b in d.tblComidaPreferidas
 from c in d.tblLugarNacimientoes
 select new
 {
 _nombre = a.Nombre,
 _comida = b.ComidaPreferida,
 _lNacimiento = c.Ciudad
 };
 foreach (var i in query)
 {
 Console.WriteLine($"{i._nombre } le gusta {i._comida} y nació en {i._lNacimiento}");
 }
</code></pre>

blocks|key|2898779|text|已经有一段时间了，但我的答案可能会对某些人有所帮助：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2898780|如果您已经正确定义了关系，则可以使用以下代码：|2898781|++++++++var+res+=+query.Products.Select(m+=>+new
++++++++{
++++++++++++productID+=+product.Id,
++++++++++++categoryID+=+m.ProductCategory.Select(s+=>+s.Category.ID).ToList(),
++++++++}).ToList();|code-block|syntax|javascript|2898782|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

it has been a while but my answer may help someone:

if you already defined the relation properly you can use this:

<pre><code> var res = query.Products.Select(m =&gt; new
 {
 productID = product.Id,
 categoryID = m.ProductCategory.Select(s =&gt; s.Category.ID).ToList(),
 }).ToList();
</code></pre>

I am trying to perform a Join between multiple tables in LINQ. I have the following classes:

<pre><code>Product {Id, ProdName, ProdQty}

Category {Id, CatName}

ProductCategory{ProdId, CatId} //association table
</code></pre>

And I use the following code (where <code>product</code>, <code>category</code> and <code>productcategory</code> are instances of the above classes):

<pre><code>var query = product.Join(productcategory, p =&gt; p.Id, pc =&gt; pc.ProdID, (p, pc) =&gt; new {product = p, productcategory = pc})
 .Join(category, ppc =&gt; ppc.productcategory.CatId, c =&gt; c.Id, (ppc, c) =&gt; new { productproductcategory = ppc, category = c});
</code></pre>

With this code I obtain an object from the following class:

<pre><code>QueryClass { productproductcategory, category}
</code></pre>

Where producproductcategory is of type:

<pre><code>ProductProductCategoryClass {product, productcategory}
</code></pre>

I do not understand where the joined "table" is, I was expecting a single class that contains all the properties from the involved classes. 

My aim is to populate another object with some properties resulting from the query: 

<pre><code>CategorizedProducts catProducts = query.Select(m =&gt; new { m.ProdId = ???, m.CatId = ???, //other assignments });
</code></pre>

how can I achieve this goal?

How to perform Join between multiple tables in LINQ lambda

数据库

我正尝试在LINQ中的多个表之间执行连接。我有以下几个类：Product {Id, ProdName, ProdQty}Category {Id, CatName}ProductCategory{ProdId, CatId} //association table我使用以下代码(其中product、category和p...

问如何在LINQ lambda中实现多个表的连接
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