将 IEntityTypeConfiguration 与基本实体一起使用

Question

在 EF Core 2.0 中，我们能够从 IEntityTypeConfiguration 派生以获得更清晰的 Fluent API 映射 (source)。

如何扩展此模式以利用基本实体？在下面的示例中，我如何使用BaseEntityConfiguration 来减少LanguageConfiguration 和MaintainerConfiguration 中的重复，仅修改BaseEntity 中的属性BaseEntityConfiguration？这样的BaseEntityConfiguration 会是什么样子？如果有的话，它将如何在OnModelCreating() 中使用？请参阅示例末尾附近的代码中的 TODO。

例子：

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）？

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

还有一种方法可以解决这个问题，那就是使用模板法设计模式。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，您无需在子配置中编写任何单行代码。

Answer 3

如果您不想为所有继承自同一基本实体的模型重复列定义，则另一种方法是：

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 ");
        // …

}

就是找到所有继承自基础Entity的Entites，遍历它们并调用通用方法，如下图，其中放置了冗余的Logic：

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;
}

在我看来它有点 hacky，但对我来说很好用！

更详细的来源：

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，以实现类似的结果。

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 GETUTCDATE，字符串为“SystemGenerated”。使用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 (4) 属性名称。然后，在我的主要映射设置完成后，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 以查看该类型是否继承自我的 BaseEntity 并在 PropertyBuilder 上设置默认值。

我直接通过 EF Migrations 对此进行了测试，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");
    }
}

这是获取给定类型的属性名称的静态帮助器。

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;
    }
}