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ConcurrencyCheck Attribute:

ConcurrencyCheck attribute can be applied to a property of a domain class. Code First takes the value of a column in "where" clause when EF executes update command for the table. You can use ConcurrencyCheck attribute when you want to use existing column for concurrency check and not a separate timestamp column for concurrency.

Consider the following example.

using System.ComponentModel.DataAnnotations;

public class Student
{
    public Student()
    { 
        
    }

    public int StudentId { get; set; }
     
    [ConcurrencyCheck]
    public string StudentName { get; set; }
}

As you can see in the above example, ConcurrencyCheck attribute is applied to existing StudentName property of the Student class. So, Code-First will include StudentName column in update command to check for optimistic concurrency.

exec sp_executesql N‘UPDATE [dbo].[Students]
SET [StudentName] = @0
WHERE (([StudentId] = @1) AND ([StudentName] = @2))
‘,N‘@0 nvarchar(max) ,@1 int,@2 nvarchar(max) ‘,@0=N‘Steve‘,@1=1,@2=N‘Bill‘
go    

Note that TimeStamp attribute can only be applied to a single byte array property in a class, whereas ConcurrencyCheck attribute can be applied to any number of properties with any datatype.

Entity Framework Code-First（9.3）：ConcurrencyCheck Attribute

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原文地址：http://www.cnblogs.com/purplefox2008/p/5644125.html