c# – 使用SQLite更新EF Core应用程序中的实体会产生DbUpdateConcurrencyException

我尝试使用sqlite在EF Core中使用乐观并发检查.
最简单的积极场景(即使没有并发本身)也给了我
Microsoft.EntityFrameworkCore.dbupdateConcurrencyException：’数据库操作预计会影响1行但实际上影响了0行.自加载实体以来,数据可能已被修改或删除.

实体：

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

语境：

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'
        }

    }
}

我怀疑它与EF和sqlite之间的数据类型有关.
日志记录在我的更新中给出了以下查询：

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Id和Timestamp的列类型都是BLOB(sqlite不提供UUID和时间戳列类型)：

同时,如果我使用sql Server(使用注释连接字符串remove .HasDefaultValuesql(“CURRENT_TIMESTAMP”)),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" />

我是否为并发检查错误配置了模型？
这让我很疯狂,因为我无法使用这个最简单的场景.

更新：我最终如何运作.这里只展示了一个想法,但它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
    }
}

解决方法:

看起来EF Core sqlite提供程序在将它们绑定到SQL查询参数时无法正确处理[TimeStamp](或IsRowVersion())标记的byte []属性.它使用默认的byte []到十六进制字符串转换,在这种情况下不适用 – byte []实际上是一个字符串.

首先考虑将其报告给他们的问题跟踪器.然后,直到它得到解决(如果有的话),作为一种解决方法,您可以使用以下自定义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只将它用于参数,所以在用.HasConversion(new sqliteTimestampConverter())分配后,现在db类型被认为是字符串,所以你需要添加.HasColumnType(“BLOB”) .

最终的工作映射是

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

您可以通过在OnModelCreating的末尾添加以下自定义sqlite RowVersion“约定”来避免所有这些：

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";
    }
}

所以您的房产配置可以减少到

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; }
}