c# - Entity Framework Context 6.1.3 未刷新/销毁？

Question

在此单元测试中，我将验证内容字节列的 MD5 是否已正确计算、保存和提取。

但是， Entity Framework (6.1.3) 上下文似乎没有刷新/销毁，因为在原始 SQL UPDATE 明显生效之后，但在使用新上下文获取行时未显示。

namespace UnitTests
{
    [TestClass]
    public class TestDataPacketServiceDebug
    {
        [TestInitialize]
        public void Setup()
        {
            CommonMethods.ResetDatabase();
            try
            {
                CommonMethods.ResetDataPacketDirectory();
            }
            catch (DirectoryNotFoundException)
            {
            }
        }

        [TestCategory("DataPacketService"), TestMethod]
        public void TestGetLocalFilePathDebug()
        {
            // Persist a DataPacket
            int dataPacketId;
            using (var testDBContext = new TestDBContext())
            {
                DataPacket dataPacket = new DataPacket
                {
                    Content = File.ReadAllBytes(@"Resources\SampleResources.zip"),
                    Description = "DataPacketSample consist of some random found .DLL files on disk",
                    Name = "SampleResources",
                    Version = "1"
                };
                testDBContext.DataPackets.Add(dataPacket);
                testDBContext.SaveChanges();
                dataPacketId = dataPacket.DataPacketId;
            }

            // Verify file path extraction
            using (var testDBContext = new TestDBContext())
            {
                DataPacket dataPacket = DataPacketService.GetByNameAndVersion("SampleResources", "1",
                    testDBContext);

                string extractedFilePath = DataPacketService.GetLocalFilePath(testDBContext,
                    dataPacket, "EntityFramework.dll");

                string validDestinationPath = String.Format(@"{0}\DataPackets\{1}_v{2}\EntityFramework.dll",
                    AppDomain.CurrentDomain.BaseDirectory, dataPacket.Name, dataPacket.Version);

                Assert.AreEqual(validDestinationPath, extractedFilePath);

                if (File.Exists(extractedFilePath) == false)
                {
                    Assert.Fail("SampleResources was not extracted correctly");
                }
            }
            // When setting a breakpoint here and take a look with external SQL Browser
            // (e.g. Microsoft SQL Server Management Studio), following is in order:
            // Note! Not all columns are shown
            // -----------------------------------------------------------------------------------------------
            // DataPacketId | Name            | RowVersion | Content     | MD5                      | Version
            //            1 | SampleResources | NULL       | 0x504B03... | 2zSV8IChaiyf0UfnezDHKg== | 1


            // Manually modify MD5 field in database for MD5 verification
            using (var testDBContext = new TestDBContext())
            {
                string sqlUpdate = String.Format("UPDATE dbo.DataPackets SET MD5 = 'another_MD5' WHERE DataPacketId = {0}",
                    dataPacketId);
                testDBContext.Database.ExecuteSqlCommand(sqlUpdate);
            }
            // When setting a breakpoint here we can clearly see that the row has been changed:
            // Note! Not all columns are shown
            // ----------------------------------------------------------------------------------
            // DataPacketId | Name            | RowVersion | Content     | MD5         | Version
            //            1 | SampleResources | NULL       | 0x504B03... | another_MD5 | 1

            // Verify MD5
            using (var testDBContext = new TestDBContext())
            {   
                // Fetch dataPacket with modified MD5
                DataPacket dataPacket = DataPacketService.GetByNameAndVersion("SampleResources", "1", testDBContext);

                // Verify that the raw SQL command has been successful:
                Assert.AreEqual("another_MD5", dataPacket.MD5);
                // BANG!!!!!!!!!!!!!!
                // Result Message:  Assert.AreEqual failed. Expected:< another_MD5 >.Actual:< 2zSV8IChaiyf0UfnezDHKg== >.
            }
        }
    }
}

实体:

public class DataPacket
{
    /// <summary>
    /// Identifier
    /// </summary>
    public int DataPacketId { get; set; }

    /// <summary>
    /// Concurrency Token
    /// </summary>
    public byte[] RowVersion { get; set; }

    /// <summary>
    /// Name
    /// </summary>
    public string Name { get; set; }

    /// <summary>
    /// Description of data packet
    /// </summary>
    public string Description { get; set; }

    /// <summary>
    /// Version of data packet
    /// </summary>
    public string Version { get; set; }

    /// <summary>
    /// MD5 of the data packet (i.e. MD5 of Content byte array)
    /// </summary>
    public string MD5 { get; private set; }

    private byte[] content;

    /// <summary>
    /// Byte content of the data packet (i.e. 
    /// </summary>
    public byte[] Content
    {
        get { return content; }
        set
        {
            content = value;
            UpdateMD5();
        }
    }

    /// <summary>
    /// TestCase navigation DataPacket <== One-To-Many ==> TestCases
    /// </summary>
    public ICollection<TestCase> TestCases { get; set; } // DataPacket <== One-To-Many ==> TestCases

    /// <summary>
    /// Update MD5 checksum depending on content
    /// </summary>
    private void UpdateMD5()
    {
        if (content != null)
        {
            this.MD5 = GetMD5ForBytes(content);
        }
    }

    /// <summary>
    /// Get MD5 checksum for content byte array
    /// </summary>
    /// <param name="content">Content byte array</param>
    /// <returns>MD5 checksum</returns>
    public static String GetMD5ForBytes(byte[] content)
    {
        if (content != null)
        {
            System.Security.Cryptography.MD5 md5Object = System.Security.Cryptography.MD5.Create();
            return System.BitConverter.ToString(md5Object.ComputeHash(content)).Replace("-", "");
        }

        return null;
    }
}

GetByNameAndVersion

public static DataPacket GetByNameAndVersion(string name, string version, TestDBContext testDBContext)
        {
            IQueryable<DataPacket> query = testDBContext.Set<DataPacket>();
            query = query.Where(t => t.Name == name).Where(t => t.Version == version);
            return query.Single();
        }

注意!我正在使用 localDB 数据库。

Answer 1

这不是 EF 上下文问题(它按预期工作)，而是您的 DataPacket 类中的错误测试/逻辑。

您有两个相关属性，都映射到数据库表列:

/// <summary>
/// MD5 of the data packet (i.e. MD5 of Content byte array)
/// </summary>
public string MD5 { get; private set; }

private byte[] content;

/// <summary>
/// Byte content of the data packet (i.e. 
/// </summary>
public byte[] Content
{
    get { return content; }
    set
    {
        content = value;
        UpdateMD5();
    }
}

客户端 C# 代码只能设置 Content 进而更新 MD5 - 没问题。但是当 EF 从数据库加载实体时会发生什么？实际上，它使用相同的属性 setter (private 不是问题，因为 EF 使用反射/代码生成，因此它可以从外部调用任何类型的 setter )。

现在一切都取决于调用 setter 的顺序。在您的情况下，首先调用 MD5，然后调用 Content。由于您的 SQL 命令更新了 MD5 列，但保持 Content 不变，因此第一个 setter 将从数据库中设置 MD5 值，第二个setter 将从 Content 更新回来。当然是哪个导致断言报告失败。

由您决定通过 SQL 更新数据库中的 MD5 列是否是有效操作(基本上将 MD5 和 Content 排除在外的同步)。在未定义的情况下调用属性 setter 的顺序 - 目前，如果您将 MD5 属性声明移动到 Content 属性之后，测试将通过，但这是您不能依赖的。