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; }
}
原文地址：https://codeday.me/bug/20190627/1303508.html
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