Question

我的查询包含以下内容

 var myvar = from table in MyDataModel
             where.....
             select new MyModel
             {
                  modelvar1 = ...,
                  modelvar2 = (from..... into anothervar)
             }

我想要做的是让modelvar2成为我目前从anothervar获取的结果与MyDataModel中另一个表之间的连接。

由于

Answer 1

括号看起来更像是子查询而不是连接。这是你加入的方式。
AdventureWorks database。

中的示例表

using (DataClasses1DataContext context = new DataClasses1DataContext())
{
    // If you have foreign keys correctly in your database you can
    // join implicitly with the "dot" notation.
    var myvar = from prod in context.Products
                where prod.ListPrice < 10
                select new
                {
                    Name = prod.Name,
                    Category = prod.ProductSubcategory.ProductCategory.Name,
                };

    // If you don't have foreign keys you need to express the join
    // explicitly like this
    var myvar2 = from prod in context.Products
                join prodSubCategory in context.ProductSubcategories
                on prod.ProductSubcategoryID equals prodSubCategory.ProductSubcategoryID
                join prodCategory in context.ProductCategories
                on prodSubCategory.ProductCategoryID equals prodCategory.ProductCategoryID
                where prod.ListPrice < 10
                select new
                {
                    Name = prod.Name,
                    Category = prodCategory.Name,
                };

    // If you REALLY want to do a subquery, this is how to do that
    var myvar3 = from prod in context.Products
                 where prod.ListPrice < 10
                 select new
                 {
                     Name = prod.Name,
                     Category = (from prodSubCategory in context.ProductSubcategories
                                 join prodCategory in context.ProductCategories
                                 on prodSubCategory.ProductCategoryID equals prodCategory.ProductCategoryID
                                 select prodCategory.Name).First(),
                 };

    // If you want to get a list from the subquery you can do like this
    var myvar4 = from prodCategory in context.ProductCategories
                select new
                {
                    Name = prodCategory.Name,
                    Subcategoreis = (from prodSubCategory in context.ProductSubcategories
                                    where prodSubCategory.ProductCategoryID == prodCategory.ProductCategoryID
                                    select new { prodSubCategory.ProductSubcategoryID, prodSubCategory.Name }).ToList(),
                };

}

Answer 2

SELECT [t0].[OrderID], [t0].[CustomerID], [t0].[EmployeeID], [t0].[OrderDate], [t0].[RequiredDate], [t0].[ShippedDate], [t0].[ShipVia], [t0].[Freight], [t0].[ShipName], [t0].[ShipAddress], [t0].[ShipCity], [t0].[ShipRegion], [t0].[ShipPostalCode], [t0].[ShipCountry]
FROM [Orders] AS [t0]
INNER JOIN ([Order Details] AS [t1]
    INNER JOIN [Products] AS [t2] ON [t1].[ProductID] = [t2].[ProductID]) ON [t0].[OrderID] = [t1].[OrderID]

可写为

from o in Orders
join od in (
    from od in OrderDetails join p in Products on od.ProductID equals p.ProductID select od) 
    on o.OrderID equals od.OrderID
select o

linq嵌套查询

2 个答案: