c# - 错误 : LINQ to Entities does not recognize the method DataLength

Question

我有一个简短的问题。首先使用 EF6 模型。

var db = new MyEntities(GetEntityConnectionString());

ObjectContext objectContext = ((IObjectContextAdapter)db).ObjectContext;
ObjectSet<DOCUMENT> objectSet = objectContext.CreateObjectSet<DOCUMENT>();
var results = objectSet.Where("SqlServer.DATALENGTH(it.BINARYCONTENT)>50000");
Assert.IsTrue(results.ToList().Count == 9);

var results2 = objectSet.Where(doc=>System.Data.Objects.SqlClient.SqlFunctions.DataLength( doc.BINARYCONTENT)>50000);
Assert.IsTrue(results2.ToList().Count == 9);

var results3 = db.DOCUMENTS.Where(doc => System.Data.Objects.SqlClient.SqlFunctions.DataLength(doc.BINARYCONTENT) > 50000);
Assert.IsTrue(results3.ToList().Count == 9);

第一个assert成功了，为什么results2和results 3执行的时候会出现如下异常？

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

Additional information: LINQ to Entities does not recognize the method 'System.Nullable`1[System.Int32] DataLength(Byte[])' method, and this method cannot be translated into a store expression.

有什么方法可以让其他断言成功吗？

Answer 1

事实证明，答案是我使用了错误的函数。

代替

System.Data.Objects.SqlClient.SqlFunctions.DataLength

我应该用

System.Data.Entity.SqlServer.SqlFunctions.DataLength

位于 EntityFramework.SqlServer.dll 中