Question

我正在尝试使用dapper的Multimapping功能返回MenuCategories和相关Menus的列表。但是我收到以下错误： -

使用多映射API时，请确保设置splitOn参数if 你有Id以外的钥匙

以下是我的课程： -

VMMenuCategory.cs

public class VMMenuCategory
    {
        public int MenuCategoryID { get; set; }
        public string CategoryName { get; set; }
        public System.DateTime CreatedOn { get; set; }
        public DateTime? UpdatedOn { get; set; }


        public List<VMMenu> Menus { get; set; }
    }

VMMenus.cs

 public class VMMenu
    {
        public int MenuID { get; set; }
        public int MenuCategoryID { get; set; }
        public string ProductName { get; set; }
        public int? CostPrice { get; set; }
        public int? SellingPrice { get; set; }
        public System.DateTime CreatedOn { get; set; }
        public DateTime? UpdatedOn { get; set; }

    }

MenuCategoriesRepository.cs

public sealed class MenuCategoryRepository : Connection, IMenuCategoryRepository
    {


        List<VMMenuCategory> IMenuCategoryRepository.GetAllMenuCategories()
        {
            List<VMMenuCategory> _lstVMMenuCategory = new List<VMMenuCategory>();
            string query = "select * from [dbo].[MenuCategories]";
            using (var connection = GetConnection())
            {
                var data = connection.Query<VMMenuCategory, VMMenu, VMMenuCategory>(query, map:(mc,m) => { mc.Menus =new List<VMMenu>() ;return mc; },splitOn: "MenuID").ToList();
                return data;
            }
            //return _lstVMMenuCategory;
        }
    }

Answer 1

为了使用来自两个表的数据填充两个对象，您必须查询两个表。在你的情况下，它很可能是内部联接：

public sealed class MenuCategoryRepository : Connection, IMenuCategoryRepository
{
    List<VMMenuCategory> IMenuCategoryRepository.GetAllMenuCategories()
    {
        List<VMMenuCategory> _lstVMMenuCategory = new List<VMMenuCategory>();
        string query = @"
            select mc.*, m.*
            from [dbo].[MenuCategories] mc,
            join [dbo].[Menus] m on mc.MenuCategoryID = m.MenuCategoryID
        ";
        using (var connection = GetConnection())
        {
            var data = connection.Query<VMMenuCategory, VMMenu, VMMenuCategory>(
               query,
               map:(mc,m) => {
                   var foundMc = _lstVMMenuCategory
                       .FirstOrDefault(x => x.MenuCategoryID = mc.MenuCategoryID);
                   if (foundMc == null) {
                       foundMc = mc;
                       foundMc.Menus = new List<VMMenu>() ;
                   }
                   foundMc.Menus.Add(m);
                   return mc; 
               },
               splitOn: "MenuID").ToList();
        }
        return _lstVMMenuCategory;
    }
}

注意：我猜测了第二个表名，并假设MenuID在Menus表定义中排在第一位。但是，最好在select子句中明确列出所有必需的列。

我还略微修改了mapper函数，以避免在类别集合中出现重复。

Answer 2

我已经更改了方法以填充分层数据。

以下是代码：

public sealed class MenuCategoryRepository : Connection, IMenuCategoryRepository
    {
        List<VMMenuCategory> IMenuCategoryRepository.GetAllMenuCategories()
        {
            List<VMMenuCategory> _lstVMMenuCategory = new List<VMMenuCategory>();
            string query = @"
            select mc.*, m.*
            from [dbo].[MenuCategories] mc
            join [dbo].[Menu] m on mc.MenuCategoryID = m.MenuCategoryID";
            using (var connection = GetConnection())
            {
                var vmMenuCategoryDictionary = new Dictionary<int, VMMenuCategory>();
                var data = connection.Query<VMMenuCategory, VMMenu, VMMenuCategory>(
                   query,
                   map: (mc, m) =>
                   {
                       VMMenuCategory _VMMenuCategory;
                       if(!vmMenuCategoryDictionary.TryGetValue(mc.MenuCategoryID,out _VMMenuCategory))
                       {
                           _VMMenuCategory = mc;
                           _VMMenuCategory.Menus = new List<VMMenu>();
                           vmMenuCategoryDictionary.Add(_VMMenuCategory.MenuCategoryID, _VMMenuCategory);

                       }
                       _VMMenuCategory.Menus.Add(m);                   
                       return _VMMenuCategory;
                   },
                   splitOn: "MenuID").Distinct().ToList();
                _lstVMMenuCategory = data;
            }
            return _lstVMMenuCategory;
        }
    }

splitOn在dapper中使用一对多关系时出错

2 个答案: