无法弄清楚为什么我会收到以下错误：
{
"title": "Server Error",
"status": 500,
"detail": "The database operation was expected to affect 1 row(s), but actually affected 0 row(s); data may have been modified or deleted since entities were loaded. See https://go.microsoft.com/fwlink/?LinkId=527962 for information on understanding and handling optimistic concurrency exceptions."
}
这是完整的例外：
Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException
HResult=0x80131500
Message=The database operation was expected to affect 1 row(s), but actually affected 0 row(s); data may have been modified or deleted since entities were loaded. See https://go.microsoft.com/fwlink/?LinkId=527962 for information on understanding and handling optimistic concurrency exceptions.
Source=Npgsql.EntityFrameworkCore.PostgreSQL
StackTrace:
at Npgsql.EntityFrameworkCore.PostgreSQL.Update.Internal.NpgsqlModificationCommandBatch.<ThrowAggregateUpdateConcurrencyExceptionAsync>d__10.MoveNext()
at Npgsql.EntityFrameworkCore.PostgreSQL.Update.Internal.NpgsqlModificationCommandBatch.<Consume>d__7.MoveNext()
at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.<ExecuteAsync>d__50.MoveNext()
at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.<ExecuteAsync>d__50.MoveNext()
at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.<ExecuteAsync>d__9.MoveNext()
at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.<ExecuteAsync>d__9.MoveNext()
at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.<ExecuteAsync>d__9.MoveNext()
at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.<SaveChangesAsync>d__111.MoveNext()
at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.<SaveChangesAsync>d__115.MoveNext()
at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlExecutionStrategy.<ExecuteAsync>d__7`2.MoveNext()
at Microsoft.EntityFrameworkCore.DbContext.<SaveChangesAsync>d__63.MoveNext()
at Persistence.IKATDbContext.<SaveEntitiesAsync>d__43.MoveNext() in C:\Users\<user>\source\repos\ikat\Persistence\IKATDbContext.cs:line 54
This exception was originally thrown at this call stack:
[External Code]
Persistence.IKATDbContext.SaveEntitiesAsync(System.Threading.CancellationToken) in IKATDbContext.cs
我是本地环境中唯一进行测试的。我按照文档工作这里
代码似乎也到位，但我肯定遗漏了一些东西。请注意，我通过删除验证等简化了代码。
我有两个实体：
public class Tutor : Entity, IAggregateRoot
{
public Guid Id { get; private set; }
public string FirstName { get; private set; }
public string LastName { get; private set; }
public ICollection<Availability> Availabilities { get; private set; }
public Tutor(string firstName, string lastName)
{
this.Id = Guid.NewGuid();
this.FirstName = firstName;
this.LastName = lastName;
this.Availabilities = [];
}
public static Tutor Create(string firstName, string lastName)
{
return new Tutor(firstName, lastName);
}
public Availability AddAvailability(DateTime startDateTime, DateTime endDateTime, bool recurring)
{
Availability availability = new(this.Id, startDateTime, endDateTime, recurring);
this.Availabilities.Add(availability);
return availability;
}
}
并且：
public class Availability : Entity
{
public Guid Id { get; private set; }
public Guid TutorId { get; private set; }
public Tutor Tutor { get; private set; }
public DateTime StartDateTime { get; private set; }
public DateTime EndDateTime { get; private set; }
public bool Recurring { get; private set; }
public Availability(Guid tutorId, DateTime startDateTime, DateTime endDateTime, bool recurring)
{
this.Id = Guid.NewGuid();
this.TutorId = tutorId;
this.StartDateTime = startDateTime;
this.EndDateTime = endDateTime;
this.Recurring = recurring;
}
}
这些是实体配置：
public class TutorEntityConfiguration : IEntityTypeConfiguration<Tutor>
{
public void Configure(EntityTypeBuilder<Tutor> builder)
{
builder.ToTable("Tutors");
builder.HasKey(t => t.Id);
builder.Property(t => t.FirstName)
.IsRequired();
builder.Property(t => t.LastName)
.IsRequired();
builder.HasMany(t => t.Availabilities)
.WithOne(a => a.Tutor)
.HasForeignKey(a => a.TutorId);
}
}
并且：
public class AvailabilityEntityConfiguration : IEntityTypeConfiguration<Availability>
{
public void Configure(EntityTypeBuilder<Availability> builder)
{
builder.ToTable("Availabilities");
builder.HasKey(a => a.Id);
builder.Property(a => a.StartDateTime)
.IsRequired();
builder.Property(a => a.EndDateTime)
.IsRequired();
builder.Property(a => a.Recurring)
.IsRequired();
builder.HasOne(a => a.Tutor)
.WithMany(t => t.Availabilities)
.HasForeignKey(a => a.TutorId)
.IsRequired();
}
}
这些是我正在使用的
TutorRepositorypublic void Update(Tutor tutor)
{
this.context.Entry(tutor).State = EntityState.Modified;
}
public async Task<Tutor> GetTutorByIdAsync(Guid tutorId, CancellationToken cancellationToken)
{
return await this.context.Tutors
.Include(t => t.Availabilities)
.FirstOrDefaultAsync(t => t.Id == tutorId, cancellationToken);
}
最后是 CommandHandler：
public async Task<Guid> Handle(CreateAvailabilityCommand request, CancellationToken cancellationToken)
{
Tutor tutor = await this.tutorRepository.GetTutorByIdAsync(request.TutorId, cancellationToken) ?? throw new Exception("Tutor not found");
tutor.AddAvailability(request.StartTime, request.EndTime, false);
this.tutorRepository.Update(tutor);
_ = await this.tutorRepository.UnitOfWork.SaveEntitiesAsync(cancellationToken);
return tutor.Id;
}
问题几乎肯定源于您映射关系的方式以及过度执行的步骤，这些步骤可能最终会在尝试插入数据时使 EF 感到困惑。 EF 将尝试遵循诸如期望名为“Id”或“{TEntity}Id”的列作为标识列之类的约定，如果您打算在代码中设置 PK 值，这可能会有点冲突。 （不推荐）存储库模式可能也不会给您带来任何好处。
过度配置关系也会让工作变得糟糕。在处理一对多等关系时，请从一侧或另一侧进行配置，而不是两者都进行配置。
对于实体配置：
public class Tutor : Entity, IAggregateRoot
{
public Guid Id { get; private set; }
public string FirstName { get; private set; }
public string LastName { get; private set; }
public ICollection<Availability> Availabilities { get; private set; } = new [];
private Tutor(string firstName, string lastName)
{
this.FirstName = firstName;
this.LastName = lastName;
}
protected Tutor () { }
public static Tutor Create(string firstName, string lastName)
{
return new Tutor(firstName, lastName);
}
public Availability AddAvailability(DateTime startDateTime, DateTime endDateTime, bool recurring)
{
Availability availability = Availability.Create(startDateTime, endDateTime, recurring);
this.Availabilities.Add(availability);
return availability;
}
}
像上面这样的东西对于工厂方法和更多 DDD 方法来聚合根来说是可以的。您应该避免在代码中分配 PK 甚至 FK。我会扩展静态工厂方法，而不是公开构造函数加工厂方法。您应该有一个受保护的默认构造函数，以使 EF 在读取数据时保持满意。它可以使用简单的值构造函数，但如果您有一个采用任何相关实体的构造函数（您可能需要一些聚合），它会犹豫不决
从那里简化实体配置：
public class TutorEntityConfiguration : IEntityTypeConfiguration<Tutor>
{
public void Configure(EntityTypeBuilder<Tutor> builder)
{
builder.ToTable("Tutors");
builder.HasKey(t => t.Id)
.DatabaseGenerated(DatabaseGeneratedOption.Identity);
builder.Property(t => t.FirstName)
.IsRequired();
builder.Property(t => t.LastName)
.IsRequired();
builder.HasMany(t => t.Availabilities)
.WithOne(a => a.Tutor)
.HasForeignKey(a => a.TutorId);
}
}
这很好，尽管我会将 Id 标记为 DatabaseGenerate Identity，其中数据库设置为默认值
NewIdNewSequentialIdDatabaseGeneratedOption.None然后在可用性配置中删除：
//builder.HasOne(a => a.Tutor)
// .WithMany(t => t.Availabilities)
// .HasForeignKey(a => a.TutorId)
// .IsRequired();
该关系是在另一端配置的，而不是在两端配置的。
现在说到保存，我真的强烈建议重新考虑添加存储库作为 EF 的抽象。您想要的最简单的形式：
var tutor = await _context.Tutors
.Include(x => x.Availabilities)
.SingleAsync(x => x.Id == tutorId);
tutor.AddAvailability(request.StartTime, request.EndTime, false);
await _context.SaveChangesAsync();
就是这样，简单直接。 EF 的
DbContextDbSet<TEntity>如果您确实想使用存储库，则应该出于正确的原因，例如集中公共域规则（如租赁、授权和/或软删除等）或更轻松地促进单元测试，而不是抽象来自您的业务逻辑/域的 EF。我用于存储库的模式是让它们公开
IQueryable<TEntity>IEnumeratble<TEntity>TEntityDbset