【EF Core】实体类的依赖注入

大叹号 發表於 2025-9-6 18:48:00

在使用外部模型那篇水文中，有大伙伴提出：老周，你那个 Ultraman 类和 Speciality 类的的关系是不是有问题，外键不应该在 Speciality 类上吗，怎么会跑到 Ultraman 类上？因为它们是一对一关系，在配置的时候你也可以反过来，主要区别是谁引用谁的问题，由于是一对一引用，所以反过来也可以的。
今天咱们聊聊实体类构造函数的依赖注入。实体类也支持依赖注入，不过，目前版本只支持注入 EF Core 自己的服务类型，你在代码中添加的应用程序级服务类型不能注入（以后可能会支持）。总结一下，以下服务类型可以注入：
1、EF Core 框架内部注册的服务类型；
2、三个补充类型：
　　a、当前 DbContext 实例（你从 DbContext 派生的类）；
　　b、当前实体相关的 IEntityType，可以获取实体模型相关信息；
　　c、ILazyLoader 接口，延时加载时用得上。
 
现在要解决一个问题：我怎么知道 EF Core 框架内部哪些服务可以注入？这个活儿有两个方案：第一个方案是看 EF Core 源代码，在 EFCore\Infrastructure 下，注意看 EntityFrameworkServicesBuilder 类的 CoreServices 字段或 TryAddCoreServices 方法，基本齐全了。
<div class="cnblogs_code">
<pre> public static readonly IDictionary<Type, ServiceCharacteristics> CoreServices
 = new Dictionary<Type, ServiceCharacteristics>
 {
 { typeof(LoggingDefinitions), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IDatabaseProvider), new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true) },
 { typeof(IDbSetFinder), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IDbSetInitializer), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IDbSetSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IEntityFinderSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IStructuralTypeMaterializerSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(ITypeMappingSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IModelCustomizer), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IModelCacheKeyFactory), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IModelSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IModelRuntimeInitializer), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IInternalEntrySubscriber), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IEntityEntryGraphIterator), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IValueGeneratorCache), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(ISingletonOptionsInitializer), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(ILoggingOptions), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(ICoreSingletonOptions), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IModelValidator), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(ICompiledQueryCache), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IValueConverterSelector), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IConstructorBindingFactory), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IRegisteredServices), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IPropertyParameterBindingFactory), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IParameterBindingFactories), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IMemberClassifier), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IMemoryCache), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IEvaluatableExpressionFilter), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(INavigationExpansionExtensibilityHelper), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(ILiftableConstantFactory), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IExceptionDetector), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IJsonValueReaderWriterSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
 { typeof(IProviderConventionSetBuilder), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IConventionSetBuilder), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IDiagnosticsLogger<>), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IInterceptors), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(ILoggerFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IEntityGraphAttacher), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IKeyPropagator), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(INavigationFixer), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(ILocalViewListener), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IStateManager), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IConcurrencyDetector), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IInternalEntityEntryNotifier), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IValueGenerationManager), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IChangeTrackerFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IChangeDetector), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IDbContextServices), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IValueGeneratorSelector), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IExecutionStrategyFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IExecutionStrategy), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IAsyncQueryProvider), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IQueryCompiler), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(ICompiledQueryCacheKeyGenerator), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IModel), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IDesignTimeModel), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IUpdateAdapterFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(ICurrentDbContext), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IDbContextDependencies), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IDatabaseFacadeDependencies), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IDbContextOptions), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IDatabase), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IDatabaseCreator), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IDbContextTransactionManager), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IQueryContextFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IQueryCompilationContextFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IQueryableMethodTranslatingExpressionVisitorFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IQueryTranslationPreprocessorFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IQueryTranslationPostprocessorFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IShapedQueryCompilingExpressionVisitorFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IDbContextLogger), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IAdHocMapper), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(ILiftableConstantProcessor), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(ILazyLoader), new ServiceCharacteristics(ServiceLifetime.Transient) },
 { typeof(ILazyLoaderFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
 { typeof(IParameterBindingFactory), new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true) },
 { typeof(ITypeMappingSourcePlugin), new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true) },
 {
 typeof(IEvaluatableExpressionFilterPlugin),
 new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true)
 },
 { typeof(ISingletonOptions), new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true) },
 { typeof(IConventionSetPlugin), new ServiceCharacteristics(ServiceLifetime.Scoped, multipleRegistrations: true) },
 { typeof(ISingletonInterceptor), new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true) },
 { typeof(IResettableService), new ServiceCharacteristics(ServiceLifetime.Scoped, multipleRegistrations: true) },
 { typeof(IInterceptor), new ServiceCharacteristics(ServiceLifetime.Scoped, multipleRegistrations: true) },
 { typeof(IInterceptorAggregator), new ServiceCharacteristics(ServiceLifetime.Scoped, multipleRegistrations: true) }
 };</pre>
</div>
这个字典的 Key 就是核心服务的类型。Relational 库和数据库提供者可能会补充一些服务，但大都多是替换服务，即接口类型是不变的。
第二个方案是通过一个叫 IRegisteredServices 的服务，它可以列出已注册服务的 Type 列表。
<div class="cnblogs_code">
<pre>using (var c = new DemoContext())
{
IRegisteredServices regsvcs = c.GetService<IRegisteredServices>
();
 foreach (var sv in regsvcs.Services)
{
 Console.WriteLine(sv);
}
……
}</pre>
</div>
这样就会列出内部已注册服务的类型。
<div class="cnblogs_code">
<pre>Microsoft.EntityFrameworkCore.Diagnostics.LoggingDefinitions
Microsoft.EntityFrameworkCore.Storage.IDatabaseProvider
Microsoft.EntityFrameworkCore.ValueGeneration.IValueGeneratorCache
Microsoft.EntityFrameworkCore.Storage.IRelationalTypeMappingSource
Microsoft.EntityFrameworkCore.Storage.ISqlGenerationHelper
Microsoft.EntityFrameworkCore.Metadata.IRelationalAnnotationProvider
Microsoft.EntityFrameworkCore.Migrations.IMigrationsAnnotationProvider
Microsoft.EntityFrameworkCore.Infrastructure.IModelValidator
Microsoft.EntityFrameworkCore.Metadata.Conventions.Infrastructure.IProviderConventionSetBuilder
Microsoft.EntityFrameworkCore.Update.IUpdateSqlGenerator
Microsoft.EntityFrameworkCore.Query.IEvaluatableExpressionFilter
Microsoft.EntityFrameworkCore.Storage.IRelationalTransactionFactory
Microsoft.EntityFrameworkCore.Update.IModificationCommandBatchFactory
Microsoft.EntityFrameworkCore.Update.IModificationCommandFactory
Microsoft.EntityFrameworkCore.ValueGeneration.IValueGeneratorSelector
Microsoft.EntityFrameworkCore.Storage.IRelationalConnection
Microsoft.EntityFrameworkCore.Migrations.IMigrationsSqlGenerator
Microsoft.EntityFrameworkCore.Storage.IRelationalDatabaseCreator
Microsoft.EntityFrameworkCore.Migrations.IHistoryRepository
Microsoft.EntityFrameworkCore.Storage.IExecutionStrategyFactory
Microsoft.EntityFrameworkCore.Query.IRelationalQueryStringFactory
Microsoft.EntityFrameworkCore.Query.ICompiledQueryCacheKeyGenerator
Microsoft.EntityFrameworkCore.Query.IQueryCompilationContextFactory
Microsoft.EntityFrameworkCore.Query.IMethodCallTranslatorProvider
Microsoft.EntityFrameworkCore.Query.IAggregateMethodCallTranslatorProvider
Microsoft.EntityFrameworkCore.Query.IMemberTranslatorProvider
Microsoft.EntityFrameworkCore.Query.IQuerySqlGeneratorFactory
Microsoft.EntityFrameworkCore.Query.IRelationalSqlTranslatingExpressionVisitorFactory
Microsoft.EntityFrameworkCore.Query.ISqlExpressionFactory
Microsoft.EntityFrameworkCore.Query.IQueryTranslationPostprocessorFactory
Microsoft.EntityFrameworkCore.Query.IRelationalParameterBasedSqlProcessorFactory
Microsoft.EntityFrameworkCore.Query.INavigationExpansionExtensibilityHelper
Microsoft.EntityFrameworkCore.Query.IQueryableMethodTranslatingExpressionVisitorFactory
Microsoft.EntityFrameworkCore.Storage.IExceptionDetector
Microsoft.EntityFrameworkCore.Infrastructure.ISingletonOptions
Microsoft.EntityFrameworkCore.SqlServer.Infrastructure.Internal.ISqlServerSingletonOptions
Microsoft.EntityFrameworkCore.SqlServer.ValueGeneration.Internal.ISqlServerValueGeneratorCache
Microsoft.EntityFrameworkCore.SqlServer.Update.Internal.ISqlServerUpdateSqlGenerator
Microsoft.EntityFrameworkCore.SqlServer.ValueGeneration.Internal.ISqlServerSequenceValueGeneratorFactory
Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.ISqlServerConnection
Microsoft.EntityFrameworkCore.Storage.IParameterNameGeneratorFactory
System.Collections.Generic.IComparer`1
Microsoft.EntityFrameworkCore.Migrations.IMigrationsIdGenerator
Microsoft.EntityFrameworkCore.Update.Internal.IRowKeyValueFactoryFactory
Microsoft.EntityFrameworkCore.Update.Internal.IRowForeignKeyValueFactoryFactory
Microsoft.EntityFrameworkCore.Update.Internal.IRowIndexValueFactoryFactory
Microsoft.EntityFrameworkCore.Update.Internal.IRowIdentityMapFactory
Microsoft.EntityFrameworkCore.Infrastructure.IModelCustomizer
Microsoft.EntityFrameworkCore.Infrastructure.IModelRuntimeInitializer
Microsoft.EntityFrameworkCore.Migrations.IMigrator
Microsoft.EntityFrameworkCore.Migrations.IMigrationCommandExecutor
Microsoft.EntityFrameworkCore.Migrations.IMigrationsAssembly
Microsoft.EntityFrameworkCore.Storage.IDatabase
Microsoft.EntityFrameworkCore.Update.IBatchExecutor
Microsoft.EntityFrameworkCore.Storage.IRelationalCommandBuilderFactory
Microsoft.EntityFrameworkCore.Storage.IRawSqlCommandBuilder
Microsoft.EntityFrameworkCore.Update.ICommandBatchPreparer
Microsoft.EntityFrameworkCore.Migrations.IMigrationsModelDiffer
Microsoft.EntityFrameworkCore.Storage.ITypeMappingSource
Microsoft.EntityFrameworkCore.Storage.IDatabaseCreator
Microsoft.EntityFrameworkCore.Storage.IDbContextTransactionManager
Microsoft.EntityFrameworkCore.Query.IQueryContextFactory
Microsoft.EntityFrameworkCore.Storage.Internal.INamedConnectionStringResolver
Microsoft.EntityFrameworkCore.Storage.IDatabaseFacadeDependencies
Microsoft.EntityFrameworkCore.Storage.IRelationalDatabaseFacadeDependencies
Microsoft.EntityFrameworkCore.Diagnostics.IRelationalConnectionDiagnosticsLogger
Microsoft.EntityFrameworkCore.Diagnostics.IDiagnosticsLogger`1
Microsoft.EntityFrameworkCore.Diagnostics.IRelationalCommandDiagnosticsLogger
Microsoft.EntityFrameworkCore.Diagnostics.IDiagnosticsLogger`1
Microsoft.EntityFrameworkCore.Diagnostics.IInterceptorAggregator
Microsoft.EntityFrameworkCore.Query.IShapedQueryCompilingExpressionVisitorFactory
Microsoft.EntityFrameworkCore.Query.IQueryTranslationPreprocessorFactory
Microsoft.EntityFrameworkCore.Metadata.IAdHocMapper
Microsoft.EntityFrameworkCore.Query.ISqlAliasManagerFactory
Microsoft.EntityFrameworkCore.Query.ILiftableConstantFactory
Microsoft.EntityFrameworkCore.Query.IRelationalLiftableConstantFactory
Microsoft.EntityFrameworkCore.Query.ILiftableConstantProcessor
Microsoft.EntityFrameworkCore.Storage.RelationalSqlGenerationHelperDependencies
Microsoft.EntityFrameworkCore.Storage.RelationalTypeMappingSourceDependencies
Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelValidatorDependencies
Microsoft.EntityFrameworkCore.Update.UpdateSqlGeneratorDependencies
Microsoft.EntityFrameworkCore.Metadata.RelationalAnnotationProviderDependencies
Microsoft.EntityFrameworkCore.Migrations.MigrationsAnnotationProviderDependencies
Microsoft.EntityFrameworkCore.Storage.ParameterNameGeneratorDependencies
Microsoft.EntityFrameworkCore.Storage.RelationalTransactionFactoryDependencies
Microsoft.EntityFrameworkCore.Storage.RelationalCommandBuilderDependencies
Microsoft.EntityFrameworkCore.Query.QuerySqlGeneratorDependencies
Microsoft.EntityFrameworkCore.Query.RelationalEvaluatableExpressionFilterDependencies
Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelDependencies
Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelRuntimeInitializerDependencies
Microsoft.EntityFrameworkCore.Query.RelationalLiftableConstantExpressionDependencies
Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGeneratorDependencies
Microsoft.EntityFrameworkCore.Metadata.Conventions.Infrastructure.RelationalConventionSetBuilderDependencies
Microsoft.EntityFrameworkCore.Update.ModificationCommandBatchFactoryDependencies
Microsoft.EntityFrameworkCore.Update.Internal.CommandBatchPreparerDependencies
Microsoft.EntityFrameworkCore.Storage.RelationalDatabaseCreatorDependencies
Microsoft.EntityFrameworkCore.Migrations.HistoryRepositoryDependencies
Microsoft.EntityFrameworkCore.Query.RelationalCompiledQueryCacheKeyGeneratorDependencies
Microsoft.EntityFrameworkCore.Query.RelationalMethodCallTranslatorProviderDependencies
Microsoft.EntityFrameworkCore.Query.RelationalAggregateMethodCallTranslatorProviderDependencies
Microsoft.EntityFrameworkCore.Query.RelationalMemberTranslatorProviderDependencies
Microsoft.EntityFrameworkCore.Query.SqlExpressionFactoryDependencies
Microsoft.EntityFrameworkCore.Query.RelationalSqlTranslatingExpressionVisitorDependencies
Microsoft.EntityFrameworkCore.Query.RelationalQueryableMethodTranslatingExpressionVisitorDependencies
Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitorDependencies
Microsoft.EntityFrameworkCore.Query.RelationalQueryTranslationPreprocessorDependencies
Microsoft.EntityFrameworkCore.Query.RelationalQueryTranslationPostprocessorDependencies
Microsoft.EntityFrameworkCore.Query.RelationalParameterBasedSqlProcessorDependencies
Microsoft.EntityFrameworkCore.Storage.RelationalConnectionDependencies
Microsoft.EntityFrameworkCore.Storage.RelationalDatabaseDependencies
Microsoft.EntityFrameworkCore.Query.RelationalQueryContextDependencies
Microsoft.EntityFrameworkCore.Query.RelationalQueryCompilationContextDependencies
Microsoft.EntityFrameworkCore.Metadata.RelationalAdHocMapperDependencies
Microsoft.EntityFrameworkCore.Infrastructure.IDbSetFinder
Microsoft.EntityFrameworkCore.Internal.IDbSetInitializer
Microsoft.EntityFrameworkCore.Internal.IDbSetSource
Microsoft.EntityFrameworkCore.Internal.IEntityFinderSource
Microsoft.EntityFrameworkCore.Query.IEntityMaterializerSource
Microsoft.EntityFrameworkCore.Metadata.Conventions.Infrastructure.IConventionSetBuilder
Microsoft.EntityFrameworkCore.Infrastructure.IModelCacheKeyFactory
Microsoft.Extensions.Logging.ILoggerFactory
Microsoft.EntityFrameworkCore.Infrastructure.IModelSource
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IInternalEntityEntrySubscriber
Microsoft.EntityFrameworkCore.ChangeTracking.IEntityEntryGraphIterator
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IEntityGraphAttacher
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IKeyPropagator
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.INavigationFixer
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.ILocalViewListener
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IStateManager
Microsoft.EntityFrameworkCore.Infrastructure.IConcurrencyDetector
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IInternalEntityEntryNotifier
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IValueGenerationManager
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IChangeTrackerFactory
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IChangeDetector
Microsoft.EntityFrameworkCore.Internal.IDbContextServices
Microsoft.EntityFrameworkCore.Internal.IDbContextDependencies
Microsoft.EntityFrameworkCore.Storage.IExecutionStrategy
Microsoft.EntityFrameworkCore.Query.Internal.ICompiledQueryCache
Microsoft.EntityFrameworkCore.Query.IAsyncQueryProvider
Microsoft.EntityFrameworkCore.Query.Internal.IQueryCompiler
Microsoft.EntityFrameworkCore.Internal.ISingletonOptionsInitializer
Microsoft.EntityFrameworkCore.Diagnostics.IDiagnosticsLogger`1
Microsoft.EntityFrameworkCore.Diagnostics.IInterceptors
Microsoft.EntityFrameworkCore.Diagnostics.ILoggingOptions
Microsoft.EntityFrameworkCore.Infrastructure.ICoreSingletonOptions
Microsoft.EntityFrameworkCore.Metadata.IModel
Microsoft.EntityFrameworkCore.Metadata.IDesignTimeModel
Microsoft.EntityFrameworkCore.Infrastructure.ICurrentDbContext
Microsoft.EntityFrameworkCore.Infrastructure.IDbContextOptions
Microsoft.EntityFrameworkCore.Infrastructure.IResettableService
Microsoft.EntityFrameworkCore.Storage.ValueConversion.IValueConverterSelector
Microsoft.EntityFrameworkCore.Metadata.IConstructorBindingFactory
Microsoft.EntityFrameworkCore.Infrastructure.Internal.ILazyLoaderFactory
Microsoft.EntityFrameworkCore.Infrastructure.ILazyLoader
Microsoft.EntityFrameworkCore.Metadata.IParameterBindingFactories
Microsoft.EntityFrameworkCore.Metadata.Internal.IMemberClassifier
Microsoft.EntityFrameworkCore.Metadata.IPropertyParameterBindingFactory
Microsoft.EntityFrameworkCore.Metadata.IParameterBindingFactory
Microsoft.Extensions.Caching.Memory.IMemoryCache
Microsoft.EntityFrameworkCore.Update.IUpdateAdapterFactory
Microsoft.EntityFrameworkCore.Storage.Json.IJsonValueReaderWriterSource
Microsoft.EntityFrameworkCore.Diagnostics.IDbContextLogger
System.Diagnostics.DiagnosticSource
Microsoft.EntityFrameworkCore.Metadata.LazyLoaderParameterBindingFactoryDependencies
Microsoft.EntityFrameworkCore.Storage.DatabaseProviderDependencies
Microsoft.EntityFrameworkCore.Infrastructure.ModelSourceDependencies
Microsoft.EntityFrameworkCore.ValueGeneration.ValueGeneratorCacheDependencies
Microsoft.EntityFrameworkCore.Infrastructure.ModelValidatorDependencies
Microsoft.EntityFrameworkCore.Storage.TypeMappingSourceDependencies
Microsoft.EntityFrameworkCore.Infrastructure.ModelCustomizerDependencies
Microsoft.EntityFrameworkCore.Infrastructure.ModelCacheKeyFactoryDependencies
Microsoft.EntityFrameworkCore.Storage.ValueConversion.ValueConverterSelectorDependencies
Microsoft.EntityFrameworkCore.Query.Internal.EntityMaterializerSourceDependencies
Microsoft.EntityFrameworkCore.Query.EvaluatableExpressionFilterDependencies
Microsoft.EntityFrameworkCore.Infrastructure.RuntimeModelDependencies
Microsoft.EntityFrameworkCore.Infrastructure.ModelRuntimeInitializerDependencies
Microsoft.EntityFrameworkCore.Query.NavigationExpansionExtensibilityHelperDependencies
Microsoft.EntityFrameworkCore.Storage.Json.JsonValueReaderWriterSourceDependencies
Microsoft.EntityFrameworkCore.Query.LiftableConstantExpressionDependencies
Microsoft.EntityFrameworkCore.Metadata.Conventions.Infrastructure.ProviderConventionSetBuilderDependencies
Microsoft.EntityFrameworkCore.Query.QueryCompilationContextDependencies
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManagerDependencies
Microsoft.EntityFrameworkCore.Storage.ExecutionStrategyDependencies
Microsoft.EntityFrameworkCore.Query.CompiledQueryCacheKeyGeneratorDependencies
Microsoft.EntityFrameworkCore.Query.QueryContextDependencies
Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitorDependencies
Microsoft.EntityFrameworkCore.Query.QueryTranslationPreprocessorDependencies
Microsoft.EntityFrameworkCore.Query.QueryTranslationPostprocessorDependencies
Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitorDependencies
Microsoft.EntityFrameworkCore.ValueGeneration.ValueGeneratorSelectorDependencies
Microsoft.EntityFrameworkCore.Storage.DatabaseDependencies
Microsoft.EntityFrameworkCore.Infrastructure.ModelDependencies
Microsoft.EntityFrameworkCore.ModelCreationDependencies
Microsoft.EntityFrameworkCore.Metadata.AdHocMapperDependencies</pre>
</div>
严重注意：实体构造函数不能注入 IRegisteredServices  类型的服务，因为 EF Core 内部实现时，本身就是从 IRegisteredServices.Services 集合中查找可以注入的服务的，而 IRegisteredServices.Services 是不包含它自己的。说人话就是：用 IRegisteredServices 类注入是找不到该服务的。
 
然后解决第二个问题：在实体类的构造函数中注入服务有啥用？大多数时候没啥用，但当你要使用某些服务来获取特殊信息，或执行特殊操作（如在实体类中执行 SQL 语句）时就用得上。
咱们举个例子，就用官方文档最喜欢的 Blog 和 Post 实体来演示。其中，Blog 类的构造函数将注入 IEntityType 服务。然后可以利用这个服务来获取 Blog 实体有几个属性，有几个键，有几个导航属性。
<div class="cnblogs_code">
<pre>public class Blog
{
// 私有字段
private IEntityType? _thisEntity;
 // 私有构造器
private Blog(IEntityType t) => _thisEntity = t;

// 公共构造器
public Blog()
{
}

public int BlogID { get; set; }
public string DisplayName { get; set; } = string.Empty;
public string Url { get; set; } = string.Empty;

public List<Post> PostList { get; set; } = new();

// 以下属性通过注入的 IEntityType 获取相关值
public int PropertyCount => _thisEntity?.GetProperties().Count() ?? 0;
public int NavigationCount => _thisEntity?.GetNavigations().Count() ?? 0;
public int KeyCount => _thisEntity?.GetKeys().Count() ?? 0;
}

public class Post
{
public int PostID { get; set; }
public string Header { get; set; } = string.Empty;
public Blog? TheBlog { get; set; }
}</pre>
</div>
注意，你自己 new 一个 Blog 实例是没有注入功能的，所以要定义一个无参数的公共构造函数，以供外部初始化用。另一个私有构造函数有一个 IEntityType 类型的参数，可以接收注入。因为这构造函数只由 EF Core 内部调用，代码中调用无法注入，故声明为私有即可。EF Core 在查找构造函数时，不管你是公有的还是私有的，只要不是静态的，一律能发现。
在访问 Blog 实体时就可以获取键、属性、导航属性的数量。
<div class="cnblogs_code">
<pre>var q = c.Blogs.Include(b => b.PostList).ToArray();
var first = q.FirstOrDefault();
if (first != null)
{
Console.WriteLine($"实体{first.GetType().Name}有{first.
PropertyCount}个属性，{first.KeyCount}个键，{first.
NavigationCount}个导航属性");
}</pre>
</div>
得到的输出如下：
<div class="cnblogs_code">
<pre>实体Blog有3个属性，1个键，1个导航属性</pre>
</div>
 
除了构造函数，也可以从属性注入。例如
<div class="cnblogs_code">
<pre>
public class Screen
{

public int ScrID { get; set; }

public int Width { get; set; }

public int Height { get; set; }

//----------- 注意以下属性 --------------
public MyDBContext? ThisContext { get; set; }
}

public class MyDBContext : DbContext
{
public MyDBContext(DbContextOptions<MyDBContext> options)
 : base(options)
{ }

public DbSet<Screen> Screens { get; set; }
}</pre>
</div>
上面示例中，MyDBContext 实例会注入到每个 Screen 实例的 ThisContext 属性。即每个实体实例的 ThisContext 属性都引用同一个 MyDBContext 对象。
<div class="cnblogs_code">
<pre>var q = dc.Screens.FirstOrDefault();
if (q != null)
{
if (q.ThisContext != null)
{
 Console.WriteLine("ThisContext属性：{0}", q.ThisContext);
}
}

// 输出：
// ThisContext属性：MyDBContext</pre>
</div>
好了，今天就水到这里了。因为这个主题确实太简单了，老周也不必举太多例子。
  
来源：https://www.cnblogs.com/tcjiaan/p/19077173

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【EF Core】实体类的依赖注入