使用SQLite更新EF Core应用程序中的实体会提供DbUpdateConcurrencyException

Question

我尝试在带有SQLite的EF Core中使用开放式并发检查。最简单的积极情况（甚至没有并发本身）也给了我 Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException: 'Database operation expected to affect 1 row(s) but actually affected 0 row(s). Data may have been modified or deleted since entities were loaded。

实体：

public class Blog
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public byte[] Timestamp { get; set; }
}

内容：

internal class Context : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlite(@"Data Source=D:\incoming\test.db");
        ///optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=Blogging;Trusted_Connection=True;");
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Blog>()
            .HasKey(p => p.Id);

        modelBuilder.Entity<Blog>()
            .Property(p => p.Timestamp)
            .IsRowVersion()
            .HasDefaultValueSql("CURRENT_TIMESTAMP");
    }
}

样品：

internal class Program
{
    public static void Main(string[] args)
    {
        var id = Guid.NewGuid();
        using (var db = new Context())
        {
            db.Database.EnsureDeleted();
            db.Database.EnsureCreated();
            db.Blogs.Add(new Blog { Id = id, Name = "1" });
            db.SaveChanges();
        }

        using (var db = new Context())
        {
            var existing = db.Blogs.Find(id);
            existing.Name = "2";
            db.SaveChanges(); // Exception thrown: 'Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException'
        }

    }
}

我怀疑这与EF和SQLite之间的数据类型有关。日志记录为我提供了有关更新的以下查询：

Executing DbCommand [Parameters=[@p1='2bcc42f5-5fd9-4cd6-b0a0-d1b843022a4b' (DbType = String), @p0='2' (Size = 1), @p2='0x323031382D31302D30372030393A34393A3331' (Size = 19) (DbType = String)], CommandType='Text', CommandTimeout='30']
UPDATE "Blogs" SET "Name" = @p0
WHERE "Id" = @p1 AND "Timestamp" = @p2;

但是列类型对于Id和Timestamp都是BLOB（SQLite不提供UUID和timestamp列类型）：

---

同时，如果我使用SQL Server（使用带注释的连接字符串+ remove .HasDefaultValueSql("CURRENT_TIMESTAMP")），则示例可以正常工作并更新数据库中的时间戳。

二手包装：

<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="2.1.4" />
<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite.Core" Version="2.1.4" />

我是否将并发检查模型配置为错误？这让我发疯，因为我无法在最简单的情况下使用它。

---

更新：我最终如何使其工作。这里仅显示想法，但可能对任何人都有帮助：

public class Blog
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public long Version { get; set; }
}

internal class Context : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlite(@"Data Source=D:\incoming\test.db");
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Blog>()
            .HasKey(p => p.Id);

        modelBuilder.Entity<Blog>()
            .Property(p => p.Version)
            .IsConcurrencyToken();
    }
}

internal class Program
{
    public static void Main(string[] args)
    {
        var id = Guid.NewGuid();
        long ver;
        using (var db = new Context())
        {
            db.Database.EnsureDeleted();
            db.Database.EnsureCreated();
            var res = db.Blogs.Add(new Blog { Id = id, Name = "xxx", Version = DateTime.Now.Ticks});
            db.SaveChanges();
        }

        using (var db = new Context())
        {
            var existing = db.Blogs.Find(id);
            existing.Name = "yyy";
            existing.Version = DateTime.Now.Ticks;
            db.SaveChanges(); // success
        }

        using (var db = new Context())
        {
            var existing = db.Blogs.Find(id);
            existing.Name = "zzz";
            existing.Version = DateTime.Now.Ticks;
            db.SaveChanges(); // success
        }

        var t1 = Task.Run(() =>
        {
            using (var db = new Context())
            {
                var existing = db.Blogs.Find(id);
                existing.Name = "yyy";
                existing.Version = DateTime.Now.Ticks;
                db.SaveChanges();
            }
        });

        var t2 = Task.Run(() =>
        {
            using (var db = new Context())
            {
                var existing = db.Blogs.Find(id);
                existing.Name = "zzz";
                existing.Version = DateTime.Now.Ticks;
                db.SaveChanges();
            }
        });

        Task.WaitAll(t1, t2); // one of the tasks throws DbUpdateConcurrencyException
    }
}

Answer 1

在将它们绑定到SQL查询参数时，似乎EF Core SQLite提供程序无法正确处理[TimeStamp]（或IsRowVersion()）标记的byte[]属性。它使用默认byte[]的十六进制 string转换，在这种情况下不适用- byte[]实际上是一个string。

首先考虑将其报告给他们的问题跟踪器。然后，直到解决（如果有），作为一种解决方法，您可以使用以下定制ValueConverter：

class SqliteTimestampConverter : ValueConverter<byte[], string>
{
    public SqliteTimestampConverter() : base(
        v => v == null ? null : ToDb(v),
        v => v == null ? null : FromDb(v))
    { }
    static byte[] FromDb(string v) =>
        v.Select(c => (byte)c).ToArray(); // Encoding.ASCII.GetString(v)
    static string ToDb(byte[] v) =>
        new string(v.Select(b => (char)b).ToArray()); // Encoding.ASCII.GetBytes(v))
}

不幸的是，没有办法告诉EF Core仅将其用于参数，因此在为其分配后.HasConversion(new SqliteTimestampConverter())，现在考虑使用db类型string，因此您需要添加.HasColumnType("BLOB")。

最终的工作映射为

    modelBuilder.Entity<Blog>()
        .Property(p => p.Timestamp)
        .IsRowVersion()
        .HasConversion(new SqliteTimestampConverter())
        .HasColumnType("BLOB")
        .HasDefaultValueSql("CURRENT_TIMESTAMP");

您可以通过在末尾添加以下自定义SQLite RowVersion“常规”来避免所有这些情况OnModelCreating：

if (Database.IsSqlite())
{
    var timestampProperties = modelBuilder.Model
        .GetEntityTypes()
        .SelectMany(t => t.GetProperties())
        .Where(p => p.ClrType == typeof(byte[])
            && p.ValueGenerated == ValueGenerated.OnAddOrUpdate
            && p.IsConcurrencyToken);

    foreach (var property in timestampProperties)
    {
        property.SetValueConverter(new SqliteTimestampConverter());
        property.Relational().DefaultValueSql = "CURRENT_TIMESTAMP";
    }
}

因此您的媒体资源配置可以调整为

modelBuilder.Entity<Blog>()
    .Property(p => p.Timestamp)
    .IsRowVersion();

或完全删除并替换为数据注释

public class Blog
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    [Timestamp]
    public byte[] Timestamp { get; set; }
}