[英]LINQ query on entities with join returning items by category
我正在使用實體框架核心。 我有以下實體:
public class Category {
public long Id { get; set; }
public string Name { get; set; }
}
public class Product {
public long Id { get; set; }
public long CategoryId { get; set; }
public string Name { get; set; }
}
我想要一個分組,其中我的鍵是我的類別,並且我有一個產品列表。 我想對數據庫運行單個查詢來執行此操作。
var data = context.Categories
.Join(
Products,
c => c.Id,
p => p.CategoryId,
(c, p) => new {
Category = c,
Product = p
}
)
.ToList();
這會運行我想要的查詢,並且似乎會生成一個包含匿名 object 的列表,該列表具有類別和產品。 如果我然后執行以下操作,它會做我想要的:
var grouped = data.GroupBy(x => new { x.Category });
鍵很好,但值列表似乎重復了類別。 有沒有辦法做到這一點,所以我有一個 Key 是 Category 然后值是 Product 對象的列表? 更喜歡方法語法,但在這一點上,如果有人能得到我,我希望能弄清楚查詢語法。
嘗試以下操作:
class Program
{
static void Main(string[] args)
{
Context context = new Context();
var results = (from c in context.Categories
join p in context.Products on c.Id equals p.CategoryId
select new { category = c, product = p })
.GroupBy(x => x.category.Id)
.ToList();
}
}
public class Context
{
public List<Category> Categories { get; set; }
public List<Product> Products { get; set; }
}
public class Category
{
public long Id { get; set; }
public string Name { get; set; }
}
public class Product
{
public long Id { get; set; }
public long CategoryId { get; set; }
public string Name { get; set; }
}
這將是一個按類別分組的產品列表
public class Category {
public long Id { get; set; }
public string Name { get; set; }
}
public class Product {
public long Id { get; set; }
public long CategoryId { get; set; }
public string Name { get; set; }
}
class Program
{
static void Main(string[] args)
{
ICollection<Category> categories = new Collection<Category>(new List<Category>());
ICollection<Product> products = new Collection<Product>(new List<Product>());
var data = categories
.Join(
products,
c => c.Id,
p => p.CategoryId,
(c, p) => new {
Category = c,
Product = p
}
)
.ToList();
var grouped = data.GroupBy(o => o.Category, o => o.Product);
}
}
正確的解決方案是這樣的:
var result = (from p in context.Products
join c in context.Categories
on p.CategoryId equals c.Id
select new
{
Product = p,
Category = c
})
.ToList() // because still grouping object is not supported in EF Core we have to materialize first and then do our grouping
.GroupBy(g => g.Category, g => g.Product)
.ToDictionary(p => p.Key, p => p.ToList());
這就是我最終解決它的方式:
var grouped = data
.GroupBy(x => new { x.Category })
.Select(x => new {
Category = x.Key.Category,
Products = x.ToList().Select(x => x.Product).ToList()
});;
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