使用实体框架阅读时出错

Question

我在使用Entity Framework从表中读取数据时遇到问题.

我想要做的是从表中读取一行Id.

这是我的SQL表定义:

CREATE TABLE [dbo].[Wares] (
    [Ware_ID]       INT           IDENTITY (1, 1) NOT NULL,
    [WareType_ID]   INT           NOT NULL,
    [Model_ID] INT           NOT NULL,
    [Ware_Price]    FLOAT (53)    CONSTRAINT [DF_Wares_Ware_Price] DEFAULT ((0)) NOT NULL,
    [Ware_Count]    INT           CONSTRAINT [DF_Wares_Ware_Count] DEFAULT ((0)) NOT NULL,
    [Ware_Brand]    NVARCHAR (30) CONSTRAINT [DF_Wares_Ware_Brand] DEFAULT (N'') NOT NULL,
    [Ware_Image]    VARCHAR (200) NULL,
    CONSTRAINT [PK_Wares] PRIMARY KEY CLUSTERED ([Ware_ID] ASC),
    CONSTRAINT [FK_Wares_WareTypes] FOREIGN KEY ([WareType_ID]) REFERENCES [dbo].[WareTypes] ([WareType_ID]) ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT [FK_Wares_Models] FOREIGN KEY ([PhoneModel_ID]) REFERENCES [dbo].[Models] ([Model_ID]) ON DELETE CASCADE ON UPDATE CASCADE
);

这是我的班级定义:

public class Ware
{
    [Key]
    public int Ware_ID { get; set; }

    public int WareType_ID { get; set; }

    public int PhoneModel_ID { get; set; }

    public float Ware_Price { get; set; }

    public int Ware_Count { get; set; }

    public string Ware_Brand { get; set; }

    public string Ware_Image { get; set; }

    public virtual WareType WareType { get; set; }
}

我想Id从查询字符串中读取并使用它来选择行:

private Ware ThisWare()
{
    string strid = Request.QueryString["id"];
    int id = Convert.ToInt32(strid);

     var context = EFDBContext.ReturnNewContext();
     var query = from m in context.Wares where m.Ware_ID == id select m;

     if (query.Count() == 1)
         return query.First();
     else return null;
}

我从行中得到错误: return query.First();

这个错误描述:

An exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll but was not handled in user code

Additional information: The 'Ware_Price' property on 'Ware' could not be set to a 'System.Double' value. You must set this property to a non-null value of type 'System.Single'.

有谁知道我怎么解决这个问题？

PS:我已经尝试改变Ware_Price,以System.Single类型,但它仍然没有奏效.

Answer 1

float(53)SQL端的A 是8个字节.甲float(又名SingleC#的一侧)为4个字节.SQL Server和.NET之间的数据类型不匹配.

'Ware'上的'Ware_Price'属性无法设置为'System.Double'值.

这意味着实体框架从表中收到了一个System.Double(double).

您必须将此属性设置为"System.Single"类型的非null值.

这意味着您的属性只能接受type System.Single(float)的值.实体框架认识到了这种差异并与之作出了反应InvalidOperationException.

要修复它,您需要将Ware_Price类中的数据类型Ware提升到a double.

我会进一步建议,对于货币价值,decimal在SQL和.NET中都是正确的数据类型,特别是如果你打算用它做任何数学计算(例如,总结大量的价格).