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[ASP.net教程]分享使用Entity Framework的一个坑:Include无效


如果不想延迟加载,可以通过设置:context.Configuration.LazyLoadingEnabled = false;或查询时加上AsNoTracking()方法即可。

如果不想生成代理,可以通过设置:context.Configuration.ProxyCreationEnabled = false;

注意当context.Configuration.ProxyCreationEnabled = false;时延迟加载也就不生效,原理很简单,因为没有代理。

当禁用延迟加载后,关联属性(导航属性)不会被实例化,这时如果需要实例化该属性,则需要通过Include方法,意为显式加载(也有人称为饥饿加载),具体的用法也可参见我之前的文章:http://www.cnblogs.com/zuowj/p/4514230.html

好了有了上面知识的了解,我们想实现一次性加载所有内容包含关联属性的值,且不要生成代理对象,就很简单了,我项目中的语句如下:

      var context = new LocalDbEntities();      context.Configuration.LazyLoadingEnabled = false;      context.Configuration.ProxyCreationEnabled = false;      result=context.Set<TA_CWTransferRequestInfo>().Where(t => true).Include(t => t.TA_CWBankAccountInfo).GroupBy(t => t.TA_CWBankAccountInfo.bkcode)          .ToDictionary(gp => gp.Key, gp => gp.ToList());

代码简单说明一下,TA_CWTransferRequestInfo有一个关联属性TA_CWBankAccountInfo,我想实现依据TA_CWBankAccountInfo.bkcode来分组并存入Dictionary中,最后我需要用到TA_CWTransferRequestInfo.TA_CWBankAccountInfo属性的信息,原本以为没有问题,但实际使用时,却报错:无法对 null 引用执行运行时绑定,经DEBUG时发现TA_CWTransferRequestInfo.TA_CWBankAccountInfo=null,这就有点不解了,明明我使用了Include,为何没有加载呢?不解之余查看了一下上述LINQ生成的SQL语句如下:

SELECT   [Project2].[C1] AS [C1],   [Project2].[bkcode] AS [bkcode],   [Project2].[C2] AS [C2],   [Project2].[id] AS [id],   [Project2].[fromactacn] AS [fromactacn],   [Project2].[toactacn] AS [toactacn],   [Project2].[toibkn] AS [toibkn],   [Project2].[toname] AS [toname],   [Project2].[toaddr] AS [toaddr],   [Project2].[tobknm] AS [tobknm],   [Project2].[tobkcode] AS [tobkcode],   [Project2].[trnamt] AS [trnamt],   [Project2].[trncur] AS [trncur],   [Project2].[priolv] AS [priolv],   [Project2].[furinfo] AS [furinfo],   [Project2].[trfdate] AS [trfdate],   [Project2].[trftime] AS [trftime],   [Project2].[comacn] AS [comacn],   [Project2].[field1] AS [field1],   [Project2].[field2] AS [field2],   [Project2].[field3] AS [field3],   [Project2].[field4] AS [field4],   [Project2].[field5] AS [field5],   [Project2].[field6] AS [field6],   [Project2].[field7] AS [field7],   [Project2].[field8] AS [field8],   [Project2].[processing] AS [processing],   [Project2].[transtype] AS [transtype],   [Project2].[trfmode] AS [trfmode],   [Project2].[createdt] AS [createdt],   [Project2].[lastupdatedt] AS [lastupdatedt],   [Project2].[lastrspid] AS [lastrspid],   [Project2].[rowversion] AS [rowversion],   [Project2].[lyd_guid] AS [lyd_guid]  FROM ( SELECT     [Distinct1].[bkcode] AS [bkcode],     1 AS [C1],     [Join2].[id] AS [id],     [Join2].[fromactacn] AS [fromactacn],     [Join2].[toactacn] AS [toactacn],     [Join2].[toibkn] AS [toibkn],     [Join2].[toname] AS [toname],     [Join2].[toaddr] AS [toaddr],     [Join2].[tobknm] AS [tobknm],     [Join2].[tobkcode] AS [tobkcode],     [Join2].[trnamt] AS [trnamt],     [Join2].[trncur1] AS [trncur],     [Join2].[priolv] AS [priolv],     [Join2].[furinfo] AS [furinfo],     [Join2].[trfdate] AS [trfdate],     [Join2].[trftime] AS [trftime],     [Join2].[comacn] AS [comacn],     [Join2].[field11] AS [field1],     [Join2].[field21] AS [field2],     [Join2].[field31] AS [field3],     [Join2].[field41] AS [field4],     [Join2].[field51] AS [field5],     [Join2].[field6] AS [field6],     [Join2].[field7] AS [field7],     [Join2].[field8] AS [field8],     [Join2].[processing] AS [processing],     [Join2].[transtype] AS [transtype],     [Join2].[trfmode] AS [trfmode],     [Join2].[createdt] AS [createdt],     [Join2].[lastupdatedt1] AS [lastupdatedt],     [Join2].[lastrspid] AS [lastrspid],     [Join2].[rowversion1] AS [rowversion],     [Join2].[lyd_guid] AS [lyd_guid],     CASE WHEN ([Join2].[priolv] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C2]    FROM  (SELECT DISTINCT       [Extent2].[bkcode] AS [bkcode]      FROM [dbo].[TA_CWTransferRequestInfo] AS [Extent1]      INNER JOIN [dbo].[TA_CWBankAccountInfo] AS [Extent2] ON [Extent1].[fromactacn] = [Extent2].[actacn] ) AS [Distinct1]    LEFT OUTER JOIN (SELECT [Extent3].[id] AS [id], [Extent3].[fromactacn] AS [fromactacn], [Extent3].[toactacn] AS [toactacn], [Extent3].[toibkn] AS [toibkn], [Extent3].[toname] AS [toname], [Extent3].[toaddr] AS [toaddr], [Extent3].[tobknm] AS [tobknm], [Extent3].[tobkcode] AS [tobkcode], [Extent3].[trnamt] AS [trnamt], [Extent3].[trncur] AS [trncur1], [Extent3].[priolv] AS [priolv], [Extent3].[furinfo] AS [furinfo], [Extent3].[trfdate] AS [trfdate], [Extent3].[trftime] AS [trftime], [Extent3].[comacn] AS [comacn], [Extent3].[field1] AS [field11], [Extent3].[field2] AS [field21], [Extent3].[field3] AS [field31], [Extent3].[field4] AS [field41], [Extent3].[field5] AS [field51], [Extent3].[field6] AS [field6], [Extent3].[field7] AS [field7], [Extent3].[field8] AS [field8], [Extent3].[processing] AS [processing], [Extent3].[transtype] AS [transtype], [Extent3].[trfmode] AS [trfmode], [Extent3].[createdt] AS [createdt], [Extent3].[lastupdatedt] AS [lastupdatedt1], [Extent3].[lastrspid] AS [lastrspid], [Extent3].[rowversion] AS [rowversion1], [Extent3].[lyd_guid] AS [lyd_guid], [Extent4].[bkcode] AS [bkcode]      FROM [dbo].[TA_CWTransferRequestInfo] AS [Extent3]      INNER JOIN [dbo].[TA_CWBankAccountInfo] AS [Extent4] ON [Extent3].[fromactacn] = [Extent4].[actacn] ) AS [Join2] ON ([Distinct1].[bkcode] = [Join2].[bkcode]) OR (1 = 0)  ) AS [Project2]  ORDER BY [Project2].[bkcode] ASC, [Project2].[C2] ASC

看到这个SQL语句我也是醉了,与我的本意完全不同,从上面的SQL语句可以看出来:它虽然关联时有用到[TA_CWBankAccountInfo],但最后只查出[TA_CWTransferRequestInfo]的字段,当然也就无法实例化关联的TA_CWBankAccountInfo属性了,最后得出结论,当使用GroupBy+ToDictionary时,Include方法无效。

鉴于上述结论,我将上述语句稍微作了一下调整,就成功通过测试了,更改后的语句:

      var context = new LocalDbEntities();      context.Configuration.LazyLoadingEnabled = false;      context.Configuration.ProxyCreationEnabled = false;      return context.Set<TA_CWTransferRequestInfo>().Where(t => true).Include(t => t.TA_CWBankAccountInfo).ToList().GroupBy(t => t.TA_CWBankAccountInfo.bkcode)          .ToDictionary(gp => gp.Key, gp => gp.ToList());

发现区别了没有?我只是在Include后加了一个ToList()方法就可以了,目的是先从数据库查询出符合条件的数据(包含关联的数据),然后再在本地进行GroupBy操作,可以看一下生成的SQL语句:

SELECT   [Extent1].[priolv] AS [priolv],   [Extent1].[id] AS [id],   [Extent1].[fromactacn] AS [fromactacn],   [Extent1].[toactacn] AS [toactacn],   [Extent1].[toibkn] AS [toibkn],   [Extent1].[toname] AS [toname],   [Extent1].[toaddr] AS [toaddr],   [Extent1].[tobknm] AS [tobknm],   [Extent1].[tobkcode] AS [tobkcode],   [Extent1].[trnamt] AS [trnamt],   [Extent1].[trncur] AS [trncur],   [Extent1].[furinfo] AS [furinfo],   [Extent1].[trfdate] AS [trfdate],   [Extent1].[trftime] AS [trftime],   [Extent1].[comacn] AS [comacn],   [Extent1].[field1] AS [field1],   [Extent1].[field2] AS [field2],   [Extent1].[field3] AS [field3],   [Extent1].[field4] AS [field4],   [Extent1].[field5] AS [field5],   [Extent1].[field6] AS [field6],   [Extent1].[field7] AS [field7],   [Extent1].[field8] AS [field8],   [Extent1].[processing] AS [processing],   [Extent1].[transtype] AS [transtype],   [Extent1].[trfmode] AS [trfmode],   [Extent1].[createdt] AS [createdt],   [Extent1].[lastupdatedt] AS [lastupdatedt],   [Extent1].[lastrspid] AS [lastrspid],   [Extent1].[rowversion] AS [rowversion],   [Extent1].[lyd_guid] AS [lyd_guid],   [Extent2].[actacn] AS [actacn],   [Extent2].[ibknum] AS [ibknum],   [Extent2].[actnam] AS [actnam],   [Extent2].[bknm] AS [bknm],   [Extent2].[bkcode] AS [bkcode],   [Extent2].[addr] AS [addr],   [Extent2].[actacnas] AS [actacnas],   [Extent2].[trncur] AS [trncur1],   [Extent2].[field1] AS [field11],   [Extent2].[field2] AS [field21],   [Extent2].[field3] AS [field31],   [Extent2].[field4] AS [field41],   [Extent2].[field5] AS [field51],   [Extent2].[lastupdatedt] AS [lastupdatedt1],   [Extent2].[rowversion] AS [rowversion1]  FROM [dbo].[TA_CWTransferRequestInfo] AS [Extent1]  INNER JOIN [dbo].[TA_CWBankAccountInfo] AS [Extent2] ON [Extent1].[fromactacn] = [Extent2].[actacn]

这个SQL语句是既简洁又明了,符合我的意图,从遇到的这个坑得到启示,有时不要把问题复杂化,换个角度看问题或许能找到更好的解决办法。