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LINQ中公共列的抽象基类

abstract-class linq sql-server .net c#

bevacqua · 技术社区 · 15 年前

这就是我目前所拥有的

using System;
using System.Collections.Generic;
using System.Data.Linq;
using System.Data.Linq.Mapping;
using System.Linq;
using System.Text;

namespace Firelight.Business
{
    public interface IBaseEntity<K>
    {
        K Id { get; }
    }

    /// <summary>
    /// Base business database connection object, primary key is int
    /// </summary>
    /// <typeparam name="T">Table name</typeparam>
    public abstract class BaseEntity<T> : BaseEntity<T, Guid> where T : class, IBaseEntity<Guid>
    {
    }

    /// <summary>
    /// Base business database connection object
    /// </summary>
    /// <typeparam name="T">Table name</typeparam>
    /// <typeparam name="K">Primary key type</typeparam>
    public abstract class BaseEntity<T,K> : IBaseEntity<K> where T : class, IBaseEntity<K>
    {
        // Avoids having to declare IBaseConnection at partial class level
        [Column(Name = "Id", CanBeNull = false, IsPrimaryKey = true, IsDbGenerated = true)]
        public K Id { get; set; } // { return default(K); }

        public static Table<T> Table 
        {
            get { return LinqUtil.Context.GetTable<T>(); } 
        }

        public static T SearchById(K id)
        {
            return Table.Single<T>(t => t.Id.Equals(id));
        }

        public static void DeleteById(K id)
        {
            Table.DeleteOnSubmit(SearchById(id));
            LinqUtil.Context.SubmitChanges();
        }
    }
}

我的问题是映射不起作用:

数据成员'系统.Guid[或系统.Int32]类型的Id' “X” 不是类型映射的一部分继承层次的根?

找不到密钥的密钥成员“Id” 或者“X”上的字段或属性

我试着把K改成Guid,结果成功了,但为什么?我看不出通用类型在这里有什么问题

所以,问题是:我怎样才能让这样的课程成功?我需要它,这样我就可以访问一个通常命名的PK(Id),它总是有类型K[它是Guid或Int32],并重构基本函数,比如select和delete by Id

编辑:

using System;
using System.Collections.Generic;
using System.Data.Linq;
using System.Linq;

namespace Firelight.Business
{
    public interface IBaseEntity<K>
    {
        K Id { get; set; }
    }

    /// <summary>
    /// Base business database connection object
    /// </summary>
    /// <typeparam name="T">Table name</typeparam>
    public abstract class BaseEntity<T> : IBaseEntity<Guid> where T : class, IBaseEntity<Guid>
    {
        // Avoids having to declare IBaseConnection at partial class level
        public Guid Id { get; set; }

        public static Table<T> Table 
        {
            get { return LinqUtil.Context.GetTable<T>(); } 
        }

        public static T SearchById(Guid id)
        {
            return Table.Single<T>(t => t.Id.Equals(id));
        }

        public static void DeleteById(Guid id)
        {
            Table.DeleteOnSubmit(SearchById(id));
            LinqUtil.Context.SubmitChanges();
        }
    }
}

我想要的基本上是相同的,用K替换Guid并使类成为BaseEntity(这样我就可以对Int32和Guid PKs使用相同的类

1 回复 | 直到 15 年前

StaceyGirl 8 年前

您所要做的将不适用于LINQ to SQL。要使用LINQ To SQL的继承,必须在基类上使用[InheritanceMapping]属性。假设有一个基类叫做Vehicle,还有一个子类叫做Motorcycle:

[InheritanceMapping(Type = typeof(Motorcycle), IsDefault = true, Code = 1)]
[Table]
public class Vehicle
{
    [Column]
    public string Make { get; set; }

    [Column]
    public string Model { get; set; }

    [Column(IsDiscriminator = true, Name="VehicleTypeId")]
    public VehicleType VehicleType { get; set; }
}

public class Motorcycle : Vehicle
{
    // implementation here
}

为了使这种继承在LINQ to SQL中工作,必须应用 [InheritanceMapping] 对基阶级您还必须有一个鉴别器列(例如,上面示例中的VehicleType)。注意,InheritanceMapping中的代码是“1”-这意味着如果数据库中的车辆类型是“1”,那么它将创建Motorcycle子类。你申请一个 [继承映射] 每个你支持的子类。

知道

更新这是有效的:

public abstract class BaseEntity<T, K> : IBaseEntity<K> where T : class, IBaseEntity<K>
{
    public abstract K Id { get; set; }

    public static Table<T> Table
    {
        get { return context.GetTable<T>(); }
    }

    public static T SearchById(K id)
    {
        return Table.Single<T>(t => t.Id.Equals(id));
    }

    public static void DeleteById(K id)
    {
        Table.DeleteOnSubmit(SearchById(id));
        context.SubmitChanges();
    }
}

注意区别是我没有 [Column] Id属性的属性。也注意到我把它抽象化了。实现类如下所示:

[Table(Name = "dbo.Contacts")]
public class Contact : BaseEntity<Contact, int>
{
    [Column]
    public override int Id { get; set; }
    [Column]
    public string FirstName { get; set; }
    [Column]
    public string LastName { get; set; }
}

Id 做有一个 [栏]

BaseEntity 具有Id属性和子类(在我的示例中 Contact