Question

我与3个表有多对多关系：

Products
Categories
ProductCategories

如何按产品获取或访问类别列表（不是ProductCategories列表）？

Answer 1

我遇到了同样的问题，我通过返回JSON_QUERY解决了它

CREATE OR ALTER PROCEDURE [Account].[GetByProduct]
    @ProductId
AS
BEGIN
    SELECT 
        P.*,
        PC.*
        JSON_QUERY((
            SELECT 
                C.*
            FOR JSON PATH
        )) AS [Categories]
    FROM 
        [Relation] AS R
        INNER JOIN [Product] AS P
        ON P.[Id] = R.[ProductRef]
        INNER JOIN [ProductCategory] AS PC
        ON PC.[Id] = R.[ProductCategoryRef]
        INNER JOIN [Category] AS C
        ON C.[Id] = AR.[CategoryRef]
    WHERE
        P.[Id] = @ProductId
END

注意：我将重命名了column＆tables以使用单数，而不是复数。

在EF Core方面，您必须使用JSON将conversion应用于列表。

Answer 2

使用这一功能对我有帮助：

var result = (from pc in ProductCategories
               join c in Categories on pc.CategoryId equals c.CategoryId 
               join p in Products on pc.ProductId equals p.ProductId 
               select new Category { //any selector you need in Category }).ToList();

Answer 3

您可以在load related data中使用import os from django.conf import settings from django.http import HttpResponse, Http404 def download(request, path): file_path = os.path.join(settings.MEDIA_ROOT, path) if os.path.exists(file_path): with open(file_path, 'rb') as fh: response = HttpResponse(fh.read(), content_type="application/vnd.ms-excel") response['Content-Disposition'] = 'inline; filename=' + os.path.basename(file_path) return response raise Http404和Include()。

例如，如果我有类似的模型

ThenInclude()

按产品访问类别列表

 public class Product
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }

    public ICollection<ProductCategory> ProductCategories { get; set; } = new List<ProductCategory>();
}

public class Category
{
    [Key]
    public int Id { get; set; }

    public string Name { get; set; }

    public ICollection<ProductCategory> ProductCategories { get; set; } = new List<ProductCategory>();

}
public class ProductCategory
{
    [Key]
    public int ProductId { get; set; }
    public Product Product { get; set; }

    [Key]
    public int CategoryId { get; set; }
    public Category Category { get; set; }
}

EF Core 2.2多对多获取相关列表

3 个答案: