c# - LINQ - 左外连接将列表附加到父对象

Question

我有:

List<Company> companies;
List<Product> products;

我想将 CompanyID 与父级匹配的相关产品对象附加到 Company.Products 列表中。请注意，公司不一定有产品。执行此操作的最高效方法是什么？林奇？

现在我正在做一个:

foreach(Company c in companies)
{
    c.Products = products.Where(x => x.CompanyID == c.CompanyID).ToList();
}

但这很慢!!

供引用的类定义:

class Company
{
    int CompanyID;
    string Name;
    List<Product> Products;
}

class Product
{
    int ProductID;
    int CompanyID;
    string ProductName;
}

Answer 1

所以你可以使用GroupJoin来做到这一点:

companies
    .GroupJoin(products, c => c.CompanyID, p => p.CompanyID, (c, pg) => 
        new Company
        {
            Products = pg.ToList(),
            CompanyID = c.CompanyID
            //other properties
        });

GroupJoin 使用散列匹配，因此它比嵌套循环更有效。

要附加这些值，您可以简单地执行以下操作:

var companiesWithProducts = companies
    .GroupJoin(products, c => c.CompanyID, p => p.CompanyID, (c, pg) => 
        new { Company = c, Products = pg });

foreach (var p in companiesWithProducts)
{
    p.Company.Products = p.Products.ToList();
}