*你能解释一下多重地图中的拆分功能吗 *
我正在尝试使用 Dapper ORM 从数据库中获取数据。我收到以下错误System.ArgumentException:使用多映射 API 时,如果您有 Id 以外的键,请确保设置 splitOn 参数参数名称:拆分上
public abstract class Domain
{
public Guid Id { get; set; }
}
public abstract class ItemBase : Domain
{
private IList<Image> images = new List<Image>();
public Guid? ParentId { get; set; }
public string Name { get; set; }
public IList<Image> Images { get { return images; } }
}
public class Meal : ItemBase
{
}
public class Item : ItemBase
{
private IList<Meal> meals = new List<Meal>();
public IList<Meal> Meals { get { return meals; } };
}
public class Image : Domain
{
public byte Img { get; set; }
public string Description { get; set; }
}
public class MealImageLink : Domain
{
public Guid ItemId { get; set; }
public Guid ImageId { get; set; }
}
/* 搜索功能从表中获取 dat */
private List<Meal> SearchMeals(Guid id)
{
var query = @"SELECT meal.[Name],meal.[Description],meal.
[Price],mealImage.[Image] as Img
FROM [MealItems] as meal
LEFT JOIN [MealImageLink] mealImageLink
on meal.Id= mealImageLink.MealItemId
LEFT JOIN [Images] mealImage on
mealImageLink.ImageId=mealImage.Id
WHERE meal.[ParentId]=@Id";
List<Meal> meals = ( _connection.Query<Meal, MealImageLink, Image, Meal>
(query, (meal, mealLink, mealImage) =>
{
meal.Images.Add(mealImage);
return meal;
}, new { @Id = id })).ToList();
return meals;
}
多地图功能实际上更适用于以下场景:
select foo.Id, foo.whatever, ...,
bar.Id, bar.something, ...,
blap.Id, blap.yada, ...
from foo ...
inner join bar ...
left outer join blap ...
或懒惰但并不少见的:
select foo.*, bar.*, blap.*
from ...
inner join bar ...
left outer join blap ...
但是在这两种情况下,都有一种清晰而明显的方法可以将水平范围拆分为分区;基本上,每当您看到名为 Id
的列时,它就是下一个块。为方便起见,名称Id
是可配置的,对于每个表具有不同主键名称(因此User
可能具有UserId
等)的情况,名称可以是分隔的列列表。
您的方案似乎与此完全不同。看起来您目前只选择了 4 列,没有特定的方法来将它们分开。我建议在这种情况下,通过不同的 API 填充模型会更容易 - 特别是dynamic
API:
var meals = new List<Meal>();
foreach(var row in _connection.Query(sql, new { @Id = id }))
{
string name = row.Name, description = row.Description;
decimal price = row.Price;
// etc
Meal meal = // TODO: build a new Meal object from those pieces
meals.Add(meal);
}
只需不指定任何<...>
即可访问dynamic
API。完成此操作后,可以按名称访问列,其类型由它们被分配给的内容所暗示 - 因此如下所示:
decimal price = row.Price;
注意:如果您想"内联"使用row
数据,那么只需尽快投射,即
// bad: forces everything to use dynamic for too long
new Meal(row.Name, row.Description, row.Price);
// good: types are nailed down immediately
new Meal((string)row.Name, (string)row.Description, (decimal)row.Price);
这有帮助吗?
Tl;dr:我只是认为多映射与您的查询无关。
编辑:这是我对你打算做什么的最佳猜测 - 它根本不适合多地图:
var meals = new List<Meal>();
foreach (var row in _connection.Query(query, new { @Id = id })) {
meals.Add(new Meal {
Name = (string)row.Name,
Images = {
new Image {
Description = (string)row.Description,
Img = (byte)row.Img
}
}
});
}
return meals;