entity-framework – 为什么EF5代码在将可空日期时间插入数据库时​​首先使用datetime2？

我将Cart对象保存到具有可为空的日期时间的数据库.这是我得到的错误：

The conversion of a datetime2 data type to a datetime data type
resulted in an out-of-range value.

有很多stackoverflow帖子记录了此问题的修复程序.但是,当代码首先创建数据库时,它将创建该字段作为DateTime(允许空值).但由于某种原因,代码首先尝试使用DateTime2字段插入.

我想知道为什么EF以单向方式创建字段,但是为同一字段使用不同类型插入.

这是域对象：

using System;
using System.Collections.Generic;

namespace Core.Domain.Cart
{
    public partial class Cart : BaseEntity,ILocalizedEntity
    {
        private ICollection<Catalog> _catalogs;

        /// <summary>
        /// Gets or sets the name
        /// </summary>
        public virtual string Name { get; set; }

        /// <summary>
        /// Gets or sets the zone identifier
        /// </summary>
        public virtual int ZoneId { get; set; }

        /// <summary>
        /// Gets or sets the brand identifier
        /// </summary>
        public virtual int BrandId { get; set; }

        /// <summary>
        /// Gets or sets the customer type identifier
        /// </summary>
        public virtual int CustomerTypeId { get; set; }

        /// <summary>
        /// Gets or sets the date and time of the opening of a cart
        /// </summary>
        public virtual DateTime? OpeningDateUtc { get; set; }

        /// <summary>
        /// Gets or sets the date and time of the closing of a cart
        /// </summary>
        public virtual DateTime? ClosingDateUtc { get; set; }

        /// <summary>
        /// Gets or sets a value indicating whether the entity is online or not
        /// </summary>
        public virtual bool IsOnline { get; set; }

        /* Truncated for relevance */
    }    
}

该模型：

using FluentValidation.Attributes;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Web.Mvc;
using Telerik.Web.Mvc;


namespace Admin.Models.Cart
{
        [Validator(typeof(CartValidator))]
        public partial class CartModel : BaseNopEntityModel,ILocalizedModel<CartLocalizedModel>
        {            
            public CartModel()
            {
                Locales = new List<CartLocalizedModel>();
                Catalogs = new List<CatalogModel>();
                UnassociatedCatalogs = new List<CatalogModel>();
            }
            [NopResourceDisplayName("Admin.Carts.Fields.Name")]
            [AllowHtml]
            public string Name { get; set; }

            //Zone dropdown
            [NopResourceDisplayName("Admin.Carts.Fields.ZoneList")]
            public SelectList ZoneList { get; set; }        //The dropdown with zones
            public int ZoneId { get; set; }                 //The selected value of the dropdown once the form is submitted
            public string ZoneName { get; set; }            //The name of the zone to display in data-grid List view.

            //Brand dropdown
            [NopResourceDisplayName("Admin.Carts.Fields.BrandList")]
            public SelectList BrandList { get; set; }       //The dropdown with brands
            public int BrandId { get; set; }                //The selected value of the dropdown once the form is submitted
            public string BrandName { get; set; }           //The name of the brand to display in the data-grid List view. 

            //Customer type dropdown
            [NopResourceDisplayName("Admin.Carts.Fields.CustomerTypeList")]
            public SelectList CustomerTypeList { get; set; }//The dropdown with CustomerType
            public int CustomerTypeId { get; set; }         //The selected value of the dropdown once the form is submitted
            public string CustomerTypeName { get; set; }    //The name of the CustomerType to display in the data-grid List view. 

            [NopResourceDisplayName("Admin.Carts.Fields.OpeningDateUtc")]
            [UIHint("DateNullable")]
            public DateTime? OpeningDateUtc { get; set; }

            [NopResourceDisplayName("Admin.Carts.Fields.ClosingDateUtc")]
            [UIHint("DateNullable")]
            public DateTime? ClosingDateUtc { get; set; }

            [NopResourceDisplayName("Admin.Carts.Fields.IsOnline")]
            public bool IsOnline { get; set; }

            /* Truncated for relevance */
        }

}

那么OpeningDateUtc和ClosingDateUtc的类型都是DateTime？.

这是EF代码首先生成数据库的方式：

OpeningDateUtc和ClosingDateUtc创建为可为空的DateTime字段.

那么为什么当我使用IDBContext.SaveChanges()进行保存时,为查询生成的SQL是：

exec sp_executesql N'update [dbo].[Cart]
set [Name] = @0,[ZoneId] = @1,[BrandId] = @2,[CustomerTypeId] = @3,[OpeningDateUtc] = @4,[ClosingDateUtc] = @5,[IsOnline] = @6,[IsReadonly] = @7,[IsPreviewMode] = @8,[CreatedOnUtc] = @9
where ([Id] = @10)
',N'@0 nvarchar(100),@1 int,@2 int,@3 int,@4 datetime2(7),@5 datetime2(7),@6 bit,@7 bit,@8 bit,@9 datetime2(7),@10 int',@0=N'Cart1',@1=7,@2=4,@3=5,@4='2013-01-09 00:00:00',@5='2013-01-18 00:00:00',@6=0,@7=0,@8=1,@9='0001-01-01 00:00:00',@10=1

有趣的部分是@ 4 datetime2(7),@ 5 datetime2(7).

我知道我可以通过在购物车地图中添加.HasColumnType(“datetime2”)来解决这个问题,但它没有回答为什么EF5(可能还有旧版本)将它们设置为可以为空的日期时间.

解决方法

.NET中的DateTime类型与SQL Server中的datetime2具有相同的范围和精度.当EF在SQL Server中插入或更新datetime或datetime2列时,它会将model属性转换为可以在.NET中保存整个DateTime范围的类型,即datetime2.如果DateTime属性不在SQL Server中的datetime范围内,则转换为datetime将失败.

顺便说一下,导致异常的问题不是两个可空的OpeningDateUtc和ClosingDateUtc列,而是SQL片段中的CreatedOnUtc值’0001-01-01 00:00:00′,即CreatedOnUtc显然未初始化在您的模型实体中. SQL Server中可以存储的日期时间最早的日期是1750年,因此0001年不适合该类型(但它适合datetime2).

因此,解决方案是将CreatedOnUtc设置为有效的日期时间值,或者 – 如您所知 – 在映射中将类型定义为datetime2.

但我同意,如果EF默认将DateTime属性映射到datetime2,则会产生更少的混淆.