将IEntityTypeConfiguration与基本实体一起使用

Question

在EF Core 2.0中，我们能够从IEntityTypeConfiguration派生出更干净的Fluent API映射(来源)。

如何扩展此模式以利用基本实体？在下面的示例中，如何使用BaseEntityConfiguration来减少LanguageConfiguration和MaintainerConfiguration中的重复，只在BaseEntityConfiguration中修改BaseEntity中的属性？这样的BaseEntityConfiguration会是什么样子；以及在OnModelCreating()中如何使用它(如果有的话)？请参阅示例末尾的代码中的TODO。

示例：

public abstract class BaseEntity
{
public long Id { get; set; }
public DateTime CreatedDateUtc { get; set; }
public DateTime? ModifiedDateUtc { get; set; }
}
public class Language : BaseEntity
{
public string Iso6392 { get; set; }
public string LocalName { get; set; }
public string Name { get; set; }
}
public class Maintainer : BaseEntity
{
public string Email { get; set; }
public string Name { get; set; }
}
public class FilterListsDbContext : DbContext
{
public FilterListsDbContext(DbContextOptions options) : base(options)
{
}
public DbSet<Language> Languages { get; set; }
public DbSet<Maintainer> Maintainers { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
//TODO: Possibly add something like BaseEntityConfiguration?
modelBuilder.ApplyConfiguration(new LanguageConfiguration());
modelBuilder.ApplyConfiguration(new MaintainerConfiguration());
}
}
public class LanguageConfiguration : IEntityTypeConfiguration<Language>
{
public void Configure(EntityTypeBuilder<Language> entityTypeBuilder)
{
//TODO: Move this to something like BaseEntityConfiguration?
entityTypeBuilder.Property(b => b.CreatedDateUtc).HasDefaultValueSql("CURRENT_TIMESTAMP");
}
}
public class MaintainerConfiguration : IEntityTypeConfiguration<Maintainer>
{
public void Configure(EntityTypeBuilder<Maintainer> entityTypeBuilder)
{
//TODO: Move this to something like BaseEntityConfiguration?
entityTypeBuilder.Property(b => b.CreatedDateUtc).HasDefaultValueSql("CURRENT_TIMESTAMP");
}
}

Answer 1

这样的东西可以工作(未经测试)吗？

public abstract class BaseEntityTypeConfiguration<TBase> : IEntityTypeConfiguration<TBase>
where TBase : BaseEntity
{
public virtual void Configure(EntityTypeBuilder<TBase> entityTypeBuilder)
{
//Base Configuration
}
}
public class MaintainerConfiguration : BaseEntityTypeConfiguration<Maintainer>
{
public override void Configure(EntityTypeBuilder<Maintainer> entityTypeBuilder)
{
entityTypeBuilder.Property(b => b.CreatedDateUtc).HasDefaultValueSql("CURRENT_TIMESTAMP");
base.Configure(entityTypeBuilder);
}
}

Answer 2

还有另一种方法可以解决这个问题，那就是使用模板方法设计模式。像这样：

public abstract class BaseEntityTypeConfiguration<TBase> : IEntityTypeConfiguration<TBase>
where TBase : BaseEntity
{
public void Configure(EntityTypeBuilder<TBase> entityTypeBuilder)
{
//Base Configuration
ConfigureOtherProperties(builder);
}
public abstract void ConfigureOtherProperties(EntityTypeBuilder<TEntity> builder);
}
public class MaintainerConfiguration : BaseEntityTypeConfiguration<Maintainer>
{
public override void ConfigureOtherProperties(EntityTypeBuilder<Maintainer> entityTypeBuilder)
{
entityTypeBuilder.Property(b => b.CreatedDateUtc).HasDefaultValueSql("CURRENT_TIMESTAMP");        
}
}

通过这种方式，您不需要在子配置中编写任何单行。

Answer 3

如果您不想重复从相同基本实体继承的所有模型的列定义，另一种方法如下：

protected override void OnModelCreating(ModelBuilder modelBuilder){
modelBuilder.Entity<Order>()
.Property(b => b.CreatedDateTime)
.HasDefaultValueSql("CURRENT_TIMESTAMP ");
modelBuilder.Entity<Adress>()
.Property(b => b.CreatedDateTime)
.HasDefaultValueSql("CURRENT_TIMESTAMP ");
// …
}

是找到从基本实体中嵌入的所有Entite，在它们上循环，并调用如下所示的通用方法，其中放置了冗余逻辑：

protected override void OnModelCreating(ModelBuilder modelBuilder){
foreach (Type type in GetEntityTypes(typeof(BaseEntity))){
var method = SetGlobalQueryMethod.MakeGenericMethod(type);
method.Invoke(this, new object[] { modelBuilder });
}
}
static readonly MethodInfo SetGlobalQueryMethod = typeof(/*your*/Context)
.GetMethods(BindingFlags.Public | BindingFlags.Instance)
.Single(t => t.IsGenericMethod && t.Name == "SetGlobalQuery");
public void SetGlobalQuery<T>(ModelBuilder builder) where T : BaseEntity{
builder.Entity<T>().Property(o => o.CreatedDateTime).HasDefaultValueSql("CURRENT_TIMESTAMP");
// Additional Statements
}

对于"GetEntityTypes"方法，您需要Nuget包"Microsoft.Extensions.DependencyModel">

private static IList<Type> _entityTypeCache;
private static IList<Type> GetEntityTypes(Type type)
{
if (_entityTypeCache != null && _entityTypeCache.First().BaseType == type)
{
return _entityTypeCache.ToList();
}
_entityTypeCache = (from a in GetReferencingAssemblies()
from t in a.DefinedTypes
where t.BaseType == type
select t.AsType()).ToList();
return _entityTypeCache;
}
private static IEnumerable<Assembly> GetReferencingAssemblies()
{
var assemblies = new List<Assembly>();
var dependencies = DependencyContext.Default.RuntimeLibraries;
foreach (var library in dependencies)
{
try
{
var assembly = Assembly.Load(new AssemblyName(library.Name));
assemblies.Add(assembly);
}
catch (FileNotFoundException)
{ }
}
return assemblies;
}

在我看来，这有点古怪，但对我来说效果很好！

更多详细信息来源：

https://www.codingame.com/playgrounds/5514/multi-tenant-asp-net-core-4---applying-tenant-rules-to-all-enitites

Answer 4

我迟到了，但这是我在OnModelCreating方法中所做的，以获得类似的结果。

基本上，我有(4)个从BaseEntity继承的属性。其中两个是日期，为什么两个是字符串。

对于日期，我希望默认为SQL的GEUTCDATE，字符串为"SystemGenerated"。使用一个允许我以强类型方式从BaseEntity检索属性名称的静态帮助程序，我获取了(4)个属性名称。然后，在设置了主映射之后，我对所有ModelBuilder实体进行迭代。这允许modelBuilder.Model.GetEntityTypes返回modelBuidler知道的实体。然后就是查看ClrType.BaseType，看看该类型是否继承自我的BaseEntity，并在PropertyBuilder上设置默认值。

我直接测试了这一点，并通过EF迁移确认生成了正确的SQL。

var createdAtUtc = StaticHelpers.GetPropertyName<BaseEntity>(x => x.CreatedAtUtc);
var lastModifiedAtUtc = StaticHelpers.GetPropertyName<BaseEntity>(x => x.LastModifiedAtUtc);
var createdBy = StaticHelpers.GetPropertyName<BaseEntity>(x => x.CreatedBy);
var lastModifiedBy = StaticHelpers.GetPropertyName<BaseEntity>(x => x.LastModifiedBy);
foreach (var t in modelBuilder.Model.GetEntityTypes())
{
if (t.ClrType.BaseType == typeof(BaseEntity))
{
modelBuilder.Entity(t.ClrType).Property(createdAtUtc).HasDefaultValueSql("GETUTCDATE()");
modelBuilder.Entity(t.ClrType).Property(lastModifiedAtUtc).HasDefaultValueSql("GETUTCDATE()");
modelBuilder.Entity(t.ClrType).Property(createdBy).HasDefaultValueSql("SystemGenerated");
modelBuilder.Entity(t.ClrType).Property(lastModifiedBy).HasDefaultValueSql("SystemGenerated");
}
}

这是用于获取给定类型的属性名称的静态帮助程序。。

public static string GetPropertyName<T>(Expression<Func<T, object>> expression)
{
if (expression.Body is MemberExpression)
{
return ((MemberExpression)expression.Body).Member.Name;
}
else
{
var op = ((UnaryExpression)expression.Body).Operand;
return ((MemberExpression)op).Member.Name;
}
}

Answer 5

具有显式接口实现的增强型解决方案：

这里有一个增强版本，它不需要您在派生配置中调用base.Configure(builder)(如接受的答案中所示)，也不需要您为每一层次结构级别的Configure方法想出一个新名称(如本答案中所述)：

我们可以通过使用显式接口实现来做到这一点：

public abstract class BaseEntityConfiguration<T> : IEntityTypeConfiguration<T> where T : BaseEntity
{
void IEntityTypeConfiguration<T>.Configure(EntityTypeBuilder<T> builder)
{
// Do all the configuration specific to `BaseEntity`
builder.Property(v => v.Id)
.Whatever();
Configure(builder);
}
protected abstract void Configure(EntityTypeBuilder<T> builder);
}

然后：

public class DerivedEntityConfiguration : BaseEntityConfiguration<DerivedEntity>
{
protected override void Configure(EntityTypeBuilder<DerivedEntity> builder)
{
// Do all the configuration specific to `DerivedEntity`
}
}

使用EF Core 7.0进行了测试，工作正常。