【发布时间】：2017-11-10 12:46:36
【问题描述】：
我正在尝试根据this answer 的想法实现一个枚举列表。我的目标是能够在我的域中使用枚举，并在从数据库中保存和检索它时将其转换为类实例。
按原样使用代码（来源如下），我得到一个带有消息的DbUpdateException：
违反主键约束“PK_dbo.Faculty”。无法在对象“dbo.Faculty”中插入重复键。重复键值为 (0)。 声明已终止。
这是意料之中的，因为我正在更新 Faculty 的每个实例。
为了解决这个问题，我尝试了解决方案
few
questions
on
this,
没有成功。他们建议附加实体或将其状态设置为未更改。所以我尝试覆盖SaveChanges() 并使用：
ChangeTracker.Entries<Faculty>().ToList().ForEach(x => x.State = EntityState.Unchanged);
和
ChangeTracker.Entries<Faculty>().ToList()
.ForEach(x => Entry(x.Entity).State = EntityState.Unchanged);
甚至
ChangeTracker.Entries<Department>().ToList().ForEach(department =>
{
foreach (var faculty in department.Entity.Faculties)
{
Entry(faculty).State = EntityState.Unchanged;
}
});
但是他们都抛出了InvalidOperationException 的消息：
附加信息：保存或接受更改失败，因为多个“TestEnum.Entities.Faculty”类型的实体具有相同的主键值。确保显式设置的主键值是唯一的。确保在数据库和实体框架模型中正确配置了数据库生成的主键。使用实体设计器进行数据库优先/模型优先配置。使用“HasDatabaseGeneratedOption”流式 API 或“DatabaseGeneratedAttribute”进行 Code First 配置。
如何指示 EF 不要尝试将它们插入数据库？我需要此实现在 SaveChanges() 内工作，因为我遵循 DDD 设计规则并将基础架构与域逻辑分开。
代码如下：
class Program
{
static void Main(string[] args)
{
using (var dbContext = new MyContext())
{
var example = new Department();
example.AddFaculty(FacultyEnum.Eng);
example.AddFaculty(FacultyEnum.Math);
dbContext.Department.Add(example);
var example2 = new Department();
example2.AddFaculty(FacultyEnum.Math);
dbContext.Department.Add(example2);
dbContext.SaveChanges();
var exampleFromDb1 = dbContext.Department.Find(1);
var exampleFromDb2 = dbContext.Department.Find(2);
}
}
}
public enum FacultyEnum
{
[Description("English")]
Eng,
[Description("Mathematics")]
Math,
[Description("Economy")]
Eco,
}
public class Department
{
public int Id { get; set; }
public virtual ICollection<Faculty> Faculties { get; set; }
public Department()
{
Faculties = new List<Faculty>();
}
public void AddFaculty(FacultyEnum faculty)
{
Faculties.Add(faculty);
}
}
public class Faculty
{
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
private Faculty(FacultyEnum @enum)
{
Id = (int)@enum;
Name = @enum.ToString();
Description = @enum.GetEnumDescription();
}
protected Faculty() { } //For EF
public static implicit operator Faculty(FacultyEnum @enum) => new Faculty(@enum);
public static implicit operator FacultyEnum(Faculty faculty) => (FacultyEnum)faculty.Id;
}
public class MyContext : DbContext
{
public DbSet<Department> Department { get; set; }
public DbSet<Faculty> Faculty { get; set; }
public MyContext()
: base(nameOrConnectionString: GetConnectionString())
{
Database.SetInitializer(new MyDbInitializer());
}
public int SaveSeed()
{
return base.SaveChanges();
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
modelBuilder.Conventions.Remove<ManyToManyCascadeDeleteConvention>();
modelBuilder.Properties<string>()
.Configure(p => p.HasMaxLength(100));
modelBuilder.Configurations.Add(new DepartmentConfiguration());
modelBuilder.Configurations.Add(new FacultyConfiguration());
base.OnModelCreating(modelBuilder);
}
private static string GetConnectionString()
{
return @"Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=TestEnum;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=True;ApplicationIntent=ReadWrite;MultiSubnetFailover=False;MultipleActiveResultSets=true;";
}
}
public class MyDbInitializer : DropCreateDatabaseIfModelChanges<MyContext>
{
protected override void Seed(MyContext context)
{
context.Faculty.SeedEnumValues<Faculty, FacultyEnum>(@enum => @enum);
context.SaveSeed();
}
}
public class DepartmentConfiguration : EntityTypeConfiguration<Department>
{
public DepartmentConfiguration()
{
HasMany(x => x.Faculties)
.WithMany();
}
}
public class FacultyConfiguration : EntityTypeConfiguration<Faculty>
{
public FacultyConfiguration()
{
Property(x => x.Id)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);
}
}
public static class Extensions
{
public static string GetEnumDescription<TEnum>(this TEnum item)
=> item.GetType()
.GetField(item.ToString())
.GetCustomAttributes(typeof(DescriptionAttribute), false)
.Cast<DescriptionAttribute>()
.FirstOrDefault()?.Description ?? string.Empty;
public static void SeedEnumValues<T, TEnum>(this IDbSet<T> dbSet, Func<TEnum, T> converter)
where T : class => Enum.GetValues(typeof(TEnum))
.Cast<object>()
.Select(value => converter((TEnum)value))
.ToList()
.ForEach(instance => dbSet.AddOrUpdate(instance));
}
【问题讨论】：
标签： c# entity-framework domain-driven-design