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首页 › 业界区 › 业界 ›【EF Core】实体类的依赖注入

【EF Core】实体类的依赖注入

笃迩讦 昨天 19:09
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。
  1.     public static readonly IDictionary<Type, ServiceCharacteristics> CoreServices
  2.         = new Dictionary<Type, ServiceCharacteristics>
  3.         {
  4.             { typeof(<strong>LoggingDefinitions</strong>), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  5.             { typeof(<strong>IDatabaseProvider</strong>), new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true) },
  6.             { typeof(<strong>IDbSetFinder</strong>), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  7.             { typeof(<strong>IDbSetInitializer</strong>), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  8.             { typeof(IDbSetSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  9.             { typeof(IEntityFinderSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  10.             { typeof(IStructuralTypeMaterializerSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  11.             { typeof(ITypeMappingSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  12.             { typeof(IModelCustomizer), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  13.             { typeof(IModelCacheKeyFactory), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  14.             { typeof(IModelSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  15.             { typeof(IModelRuntimeInitializer), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  16.             { typeof(IInternalEntrySubscriber), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  17.             { typeof(IEntityEntryGraphIterator), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  18.             { typeof(IValueGeneratorCache), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  19.             { typeof(ISingletonOptionsInitializer), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  20.             { typeof(ILoggingOptions), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  21.             { typeof(ICoreSingletonOptions), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  22.             { typeof(IModelValidator), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  23.             { typeof(ICompiledQueryCache), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  24.             { typeof(IValueConverterSelector), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  25.             { typeof(IConstructorBindingFactory), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  26.             { typeof(IRegisteredServices), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  27.             { typeof(IPropertyParameterBindingFactory), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  28.             { typeof(IParameterBindingFactories), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  29.             { typeof(IMemberClassifier), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  30.             { typeof(IMemoryCache), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  31.             { typeof(IEvaluatableExpressionFilter), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  32.             { typeof(INavigationExpansionExtensibilityHelper), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  33.             { typeof(ILiftableConstantFactory), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  34.             { typeof(IExceptionDetector), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  35.             { typeof(IJsonValueReaderWriterSource), new ServiceCharacteristics(ServiceLifetime.Singleton) },
  36.             { typeof(IProviderConventionSetBuilder), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  37.             { typeof(IConventionSetBuilder), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  38.             { typeof(IDiagnosticsLogger<>), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  39.             { typeof(IInterceptors), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  40.             { typeof(ILoggerFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  41.             { typeof(IEntityGraphAttacher), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  42.             { typeof(IKeyPropagator), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  43.             { typeof(INavigationFixer), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  44.             { typeof(ILocalViewListener), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  45.             { typeof(IStateManager), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  46.             { typeof(IConcurrencyDetector), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  47.             { typeof(IInternalEntityEntryNotifier), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  48.             { typeof(IValueGenerationManager), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  49.             { typeof(IChangeTrackerFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  50.             { typeof(IChangeDetector), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  51.             { typeof(IDbContextServices), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  52.             { typeof(IValueGeneratorSelector), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  53.             { typeof(IExecutionStrategyFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  54.             { typeof(IExecutionStrategy), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  55.             { typeof(IAsyncQueryProvider), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  56.             { typeof(IQueryCompiler), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  57.             { typeof(ICompiledQueryCacheKeyGenerator), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  58.             { typeof(IModel), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  59.             { typeof(IDesignTimeModel), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  60.             { typeof(IUpdateAdapterFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  61.             { typeof(ICurrentDbContext), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  62.             { typeof(IDbContextDependencies), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  63.             { typeof(IDatabaseFacadeDependencies), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  64.             { typeof(IDbContextOptions), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  65.             { typeof(IDatabase), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  66.             { typeof(IDatabaseCreator), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  67.             { typeof(IDbContextTransactionManager), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  68.             { typeof(IQueryContextFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  69.             { typeof(IQueryCompilationContextFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  70.             { typeof(IQueryableMethodTranslatingExpressionVisitorFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  71.             { typeof(IQueryTranslationPreprocessorFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  72.             { typeof(IQueryTranslationPostprocessorFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  73.             { typeof(IShapedQueryCompilingExpressionVisitorFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  74.             { typeof(IDbContextLogger), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  75.             { typeof(IAdHocMapper), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  76.             { typeof(ILiftableConstantProcessor), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  77.             { typeof(ILazyLoader), new ServiceCharacteristics(ServiceLifetime.Transient) },
  78.             { typeof(ILazyLoaderFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
  79.             { typeof(IParameterBindingFactory), new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true) },
  80.             { typeof(ITypeMappingSourcePlugin), new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true) },
  81.             {
  82.                 typeof(IEvaluatableExpressionFilterPlugin),
  83.                 new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true)
  84.             },
  85.             { typeof(ISingletonOptions), new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true) },
  86.             { typeof(IConventionSetPlugin), new ServiceCharacteristics(ServiceLifetime.Scoped, multipleRegistrations: true) },
  87.             { typeof(ISingletonInterceptor), new ServiceCharacteristics(ServiceLifetime.Singleton, multipleRegistrations: true) },
  88.             { typeof(IResettableService), new ServiceCharacteristics(ServiceLifetime.Scoped, multipleRegistrations: true) },
  89.             { typeof(IInterceptor), new ServiceCharacteristics(ServiceLifetime.Scoped, multipleRegistrations: true) },
  90.             { typeof(IInterceptorAggregator), new ServiceCharacteristics(ServiceLifetime.Scoped, multipleRegistrations: true) }
  91.         };
复制代码
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。
  1. using (var c = new DemoContext())
  2. {
  3.     <strong>IRegisteredServices regsvcs </strong><strong>= c.GetService<IRegisteredServices>
  4. ();
  5. </strong>    foreach (var sv in regsvcs.Services)
  6.     {
  7.         Console.WriteLine(sv);
  8.     }
  9.     ……
  10. }
复制代码
这样就会列出内部已注册服务的类型。
  1. Microsoft.EntityFrameworkCore.Diagnostics.LoggingDefinitions
  2. Microsoft.EntityFrameworkCore.Storage.IDatabaseProvider
  3. Microsoft.EntityFrameworkCore.ValueGeneration.IValueGeneratorCache
  4. Microsoft.EntityFrameworkCore.Storage.IRelationalTypeMappingSource
  5. Microsoft.EntityFrameworkCore.Storage.ISqlGenerationHelper
  6. Microsoft.EntityFrameworkCore.Metadata.IRelationalAnnotationProvider
  7. Microsoft.EntityFrameworkCore.Migrations.IMigrationsAnnotationProvider
  8. Microsoft.EntityFrameworkCore.Infrastructure.IModelValidator
  9. Microsoft.EntityFrameworkCore.Metadata.Conventions.Infrastructure.IProviderConventionSetBuilder
  10. Microsoft.EntityFrameworkCore.Update.IUpdateSqlGenerator
  11. Microsoft.EntityFrameworkCore.Query.IEvaluatableExpressionFilter
  12. Microsoft.EntityFrameworkCore.Storage.IRelationalTransactionFactory
  13. Microsoft.EntityFrameworkCore.Update.IModificationCommandBatchFactory
  14. Microsoft.EntityFrameworkCore.Update.IModificationCommandFactory
  15. Microsoft.EntityFrameworkCore.ValueGeneration.IValueGeneratorSelector
  16. Microsoft.EntityFrameworkCore.Storage.IRelationalConnection
  17. Microsoft.EntityFrameworkCore.Migrations.IMigrationsSqlGenerator
  18. Microsoft.EntityFrameworkCore.Storage.IRelationalDatabaseCreator
  19. Microsoft.EntityFrameworkCore.Migrations.IHistoryRepository
  20. Microsoft.EntityFrameworkCore.Storage.IExecutionStrategyFactory
  21. Microsoft.EntityFrameworkCore.Query.IRelationalQueryStringFactory
  22. Microsoft.EntityFrameworkCore.Query.ICompiledQueryCacheKeyGenerator
  23. Microsoft.EntityFrameworkCore.Query.IQueryCompilationContextFactory
  24. Microsoft.EntityFrameworkCore.Query.IMethodCallTranslatorProvider
  25. Microsoft.EntityFrameworkCore.Query.IAggregateMethodCallTranslatorProvider
  26. Microsoft.EntityFrameworkCore.Query.IMemberTranslatorProvider
  27. Microsoft.EntityFrameworkCore.Query.IQuerySqlGeneratorFactory
  28. Microsoft.EntityFrameworkCore.Query.IRelationalSqlTranslatingExpressionVisitorFactory
  29. Microsoft.EntityFrameworkCore.Query.ISqlExpressionFactory
  30. Microsoft.EntityFrameworkCore.Query.IQueryTranslationPostprocessorFactory
  31. Microsoft.EntityFrameworkCore.Query.IRelationalParameterBasedSqlProcessorFactory
  32. Microsoft.EntityFrameworkCore.Query.INavigationExpansionExtensibilityHelper
  33. Microsoft.EntityFrameworkCore.Query.IQueryableMethodTranslatingExpressionVisitorFactory
  34. Microsoft.EntityFrameworkCore.Storage.IExceptionDetector
  35. Microsoft.EntityFrameworkCore.Infrastructure.ISingletonOptions
  36. Microsoft.EntityFrameworkCore.SqlServer.Infrastructure.Internal.ISqlServerSingletonOptions
  37. Microsoft.EntityFrameworkCore.SqlServer.ValueGeneration.Internal.ISqlServerValueGeneratorCache
  38. Microsoft.EntityFrameworkCore.SqlServer.Update.Internal.ISqlServerUpdateSqlGenerator
  39. Microsoft.EntityFrameworkCore.SqlServer.ValueGeneration.Internal.ISqlServerSequenceValueGeneratorFactory      
  40. Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.ISqlServerConnection
  41. Microsoft.EntityFrameworkCore.Storage.IParameterNameGeneratorFactory
  42. System.Collections.Generic.IComparer`1[Microsoft.EntityFrameworkCore.Update.IReadOnlyModificationCommand]     
  43. Microsoft.EntityFrameworkCore.Migrations.IMigrationsIdGenerator
  44. Microsoft.EntityFrameworkCore.Update.Internal.IRowKeyValueFactoryFactory
  45. Microsoft.EntityFrameworkCore.Update.Internal.IRowForeignKeyValueFactoryFactory
  46. Microsoft.EntityFrameworkCore.Update.Internal.IRowIndexValueFactoryFactory
  47. Microsoft.EntityFrameworkCore.Update.Internal.IRowIdentityMapFactory
  48. Microsoft.EntityFrameworkCore.Infrastructure.IModelCustomizer
  49. Microsoft.EntityFrameworkCore.Infrastructure.IModelRuntimeInitializer
  50. Microsoft.EntityFrameworkCore.Migrations.IMigrator
  51. Microsoft.EntityFrameworkCore.Migrations.IMigrationCommandExecutor
  52. Microsoft.EntityFrameworkCore.Migrations.IMigrationsAssembly
  53. Microsoft.EntityFrameworkCore.Storage.IDatabase
  54. Microsoft.EntityFrameworkCore.Update.IBatchExecutor
  55. Microsoft.EntityFrameworkCore.Storage.IRelationalCommandBuilderFactory
  56. Microsoft.EntityFrameworkCore.Storage.IRawSqlCommandBuilder
  57. Microsoft.EntityFrameworkCore.Update.ICommandBatchPreparer
  58. Microsoft.EntityFrameworkCore.Migrations.IMigrationsModelDiffer
  59. Microsoft.EntityFrameworkCore.Storage.ITypeMappingSource
  60. Microsoft.EntityFrameworkCore.Storage.IDatabaseCreator
  61. Microsoft.EntityFrameworkCore.Storage.IDbContextTransactionManager
  62. Microsoft.EntityFrameworkCore.Query.IQueryContextFactory
  63. Microsoft.EntityFrameworkCore.Storage.Internal.INamedConnectionStringResolver
  64. Microsoft.EntityFrameworkCore.Storage.IDatabaseFacadeDependencies
  65. Microsoft.EntityFrameworkCore.Storage.IRelationalDatabaseFacadeDependencies
  66. Microsoft.EntityFrameworkCore.Diagnostics.IRelationalConnectionDiagnosticsLogger
  67. Microsoft.EntityFrameworkCore.Diagnostics.IDiagnosticsLogger`1[Microsoft.EntityFrameworkCore.DbLoggerCategory+Database+Connection]
  68. Microsoft.EntityFrameworkCore.Diagnostics.IRelationalCommandDiagnosticsLogger
  69. Microsoft.EntityFrameworkCore.Diagnostics.IDiagnosticsLogger`1[Microsoft.EntityFrameworkCore.DbLoggerCategory+Database+Command]
  70. Microsoft.EntityFrameworkCore.Diagnostics.IInterceptorAggregator
  71. Microsoft.EntityFrameworkCore.Query.IShapedQueryCompilingExpressionVisitorFactory
  72. Microsoft.EntityFrameworkCore.Query.IQueryTranslationPreprocessorFactory
  73. Microsoft.EntityFrameworkCore.Metadata.IAdHocMapper
  74. Microsoft.EntityFrameworkCore.Query.ISqlAliasManagerFactory
  75. Microsoft.EntityFrameworkCore.Query.ILiftableConstantFactory
  76. Microsoft.EntityFrameworkCore.Query.IRelationalLiftableConstantFactory
  77. Microsoft.EntityFrameworkCore.Query.ILiftableConstantProcessor
  78. Microsoft.EntityFrameworkCore.Storage.RelationalSqlGenerationHelperDependencies
  79. Microsoft.EntityFrameworkCore.Storage.RelationalTypeMappingSourceDependencies
  80. Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelValidatorDependencies
  81. Microsoft.EntityFrameworkCore.Update.UpdateSqlGeneratorDependencies
  82. Microsoft.EntityFrameworkCore.Metadata.RelationalAnnotationProviderDependencies
  83. Microsoft.EntityFrameworkCore.Migrations.MigrationsAnnotationProviderDependencies
  84. Microsoft.EntityFrameworkCore.Storage.ParameterNameGeneratorDependencies
  85. Microsoft.EntityFrameworkCore.Storage.RelationalTransactionFactoryDependencies
  86. Microsoft.EntityFrameworkCore.Storage.RelationalCommandBuilderDependencies
  87. Microsoft.EntityFrameworkCore.Query.QuerySqlGeneratorDependencies
  88. Microsoft.EntityFrameworkCore.Query.RelationalEvaluatableExpressionFilterDependencies
  89. Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelDependencies
  90. Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelRuntimeInitializerDependencies
  91. Microsoft.EntityFrameworkCore.Query.RelationalLiftableConstantExpressionDependencies
  92. Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGeneratorDependencies
  93. Microsoft.EntityFrameworkCore.Metadata.Conventions.Infrastructure.RelationalConventionSetBuilderDependencies  
  94. Microsoft.EntityFrameworkCore.Update.ModificationCommandBatchFactoryDependencies
  95. Microsoft.EntityFrameworkCore.Update.Internal.CommandBatchPreparerDependencies
  96. Microsoft.EntityFrameworkCore.Storage.RelationalDatabaseCreatorDependencies
  97. Microsoft.EntityFrameworkCore.Migrations.HistoryRepositoryDependencies
  98. Microsoft.EntityFrameworkCore.Query.RelationalCompiledQueryCacheKeyGeneratorDependencies
  99. Microsoft.EntityFrameworkCore.Query.RelationalMethodCallTranslatorProviderDependencies
  100. Microsoft.EntityFrameworkCore.Query.RelationalAggregateMethodCallTranslatorProviderDependencies
  101. Microsoft.EntityFrameworkCore.Query.RelationalMemberTranslatorProviderDependencies
  102. Microsoft.EntityFrameworkCore.Query.SqlExpressionFactoryDependencies
  103. Microsoft.EntityFrameworkCore.Query.RelationalSqlTranslatingExpressionVisitorDependencies
  104. Microsoft.EntityFrameworkCore.Query.RelationalQueryableMethodTranslatingExpressionVisitorDependencies
  105. Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitorDependencies
  106. Microsoft.EntityFrameworkCore.Query.RelationalQueryTranslationPreprocessorDependencies
  107. Microsoft.EntityFrameworkCore.Query.RelationalQueryTranslationPostprocessorDependencies
  108. Microsoft.EntityFrameworkCore.Query.RelationalParameterBasedSqlProcessorDependencies
  109. Microsoft.EntityFrameworkCore.Storage.RelationalConnectionDependencies
  110. Microsoft.EntityFrameworkCore.Storage.RelationalDatabaseDependencies
  111. Microsoft.EntityFrameworkCore.Query.RelationalQueryContextDependencies
  112. Microsoft.EntityFrameworkCore.Query.RelationalQueryCompilationContextDependencies
  113. Microsoft.EntityFrameworkCore.Metadata.RelationalAdHocMapperDependencies
  114. Microsoft.EntityFrameworkCore.Infrastructure.IDbSetFinder
  115. Microsoft.EntityFrameworkCore.Internal.IDbSetInitializer
  116. Microsoft.EntityFrameworkCore.Internal.IDbSetSource
  117. Microsoft.EntityFrameworkCore.Internal.IEntityFinderSource
  118. Microsoft.EntityFrameworkCore.Query.IEntityMaterializerSource
  119. Microsoft.EntityFrameworkCore.Metadata.Conventions.Infrastructure.IConventionSetBuilder
  120. Microsoft.EntityFrameworkCore.Infrastructure.IModelCacheKeyFactory
  121. Microsoft.Extensions.Logging.ILoggerFactory
  122. Microsoft.EntityFrameworkCore.Infrastructure.IModelSource
  123. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IInternalEntityEntrySubscriber
  124. Microsoft.EntityFrameworkCore.ChangeTracking.IEntityEntryGraphIterator
  125. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IEntityGraphAttacher
  126. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IKeyPropagator
  127. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.INavigationFixer
  128. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.ILocalViewListener
  129. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IStateManager
  130. Microsoft.EntityFrameworkCore.Infrastructure.IConcurrencyDetector
  131. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IInternalEntityEntryNotifier
  132. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IValueGenerationManager
  133. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IChangeTrackerFactory
  134. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IChangeDetector
  135. Microsoft.EntityFrameworkCore.Internal.IDbContextServices
  136. Microsoft.EntityFrameworkCore.Internal.IDbContextDependencies
  137. Microsoft.EntityFrameworkCore.Storage.IExecutionStrategy
  138. Microsoft.EntityFrameworkCore.Query.Internal.ICompiledQueryCache
  139. Microsoft.EntityFrameworkCore.Query.IAsyncQueryProvider
  140. Microsoft.EntityFrameworkCore.Query.Internal.IQueryCompiler
  141. Microsoft.EntityFrameworkCore.Internal.ISingletonOptionsInitializer
  142. Microsoft.EntityFrameworkCore.Diagnostics.IDiagnosticsLogger`1[TLoggerCategory]
  143. Microsoft.EntityFrameworkCore.Diagnostics.IInterceptors
  144. Microsoft.EntityFrameworkCore.Diagnostics.ILoggingOptions
  145. Microsoft.EntityFrameworkCore.Infrastructure.ICoreSingletonOptions
  146. Microsoft.EntityFrameworkCore.Metadata.IModel
  147. Microsoft.EntityFrameworkCore.Metadata.IDesignTimeModel
  148. Microsoft.EntityFrameworkCore.Infrastructure.ICurrentDbContext
  149. Microsoft.EntityFrameworkCore.Infrastructure.IDbContextOptions
  150. Microsoft.EntityFrameworkCore.Infrastructure.IResettableService
  151. Microsoft.EntityFrameworkCore.Storage.ValueConversion.IValueConverterSelector
  152. Microsoft.EntityFrameworkCore.Metadata.IConstructorBindingFactory
  153. Microsoft.EntityFrameworkCore.Infrastructure.Internal.ILazyLoaderFactory
  154. Microsoft.EntityFrameworkCore.Infrastructure.ILazyLoader
  155. Microsoft.EntityFrameworkCore.Metadata.IParameterBindingFactories
  156. Microsoft.EntityFrameworkCore.Metadata.Internal.IMemberClassifier
  157. Microsoft.EntityFrameworkCore.Metadata.IPropertyParameterBindingFactory
  158. Microsoft.EntityFrameworkCore.Metadata.IParameterBindingFactory
  159. Microsoft.Extensions.Caching.Memory.IMemoryCache
  160. Microsoft.EntityFrameworkCore.Update.IUpdateAdapterFactory
  161. Microsoft.EntityFrameworkCore.Storage.Json.IJsonValueReaderWriterSource
  162. Microsoft.EntityFrameworkCore.Diagnostics.IDbContextLogger
  163. System.Diagnostics.DiagnosticSource
  164. Microsoft.EntityFrameworkCore.Metadata.LazyLoaderParameterBindingFactoryDependencies
  165. Microsoft.EntityFrameworkCore.Storage.DatabaseProviderDependencies
  166. Microsoft.EntityFrameworkCore.Infrastructure.ModelSourceDependencies
  167. Microsoft.EntityFrameworkCore.ValueGeneration.ValueGeneratorCacheDependencies
  168. Microsoft.EntityFrameworkCore.Infrastructure.ModelValidatorDependencies
  169. Microsoft.EntityFrameworkCore.Storage.TypeMappingSourceDependencies
  170. Microsoft.EntityFrameworkCore.Infrastructure.ModelCustomizerDependencies
  171. Microsoft.EntityFrameworkCore.Infrastructure.ModelCacheKeyFactoryDependencies
  172. Microsoft.EntityFrameworkCore.Storage.ValueConversion.ValueConverterSelectorDependencies
  173. Microsoft.EntityFrameworkCore.Query.Internal.EntityMaterializerSourceDependencies
  174. Microsoft.EntityFrameworkCore.Query.EvaluatableExpressionFilterDependencies
  175. Microsoft.EntityFrameworkCore.Infrastructure.RuntimeModelDependencies
  176. Microsoft.EntityFrameworkCore.Infrastructure.ModelRuntimeInitializerDependencies
  177. Microsoft.EntityFrameworkCore.Query.NavigationExpansionExtensibilityHelperDependencies
  178. Microsoft.EntityFrameworkCore.Storage.Json.JsonValueReaderWriterSourceDependencies
  179. Microsoft.EntityFrameworkCore.Query.LiftableConstantExpressionDependencies
  180. Microsoft.EntityFrameworkCore.Metadata.Conventions.Infrastructure.ProviderConventionSetBuilderDependencies   
  181. Microsoft.EntityFrameworkCore.Query.QueryCompilationContextDependencies
  182. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManagerDependencies
  183. Microsoft.EntityFrameworkCore.Storage.ExecutionStrategyDependencies
  184. Microsoft.EntityFrameworkCore.Query.CompiledQueryCacheKeyGeneratorDependencies
  185. Microsoft.EntityFrameworkCore.Query.QueryContextDependencies
  186. Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitorDependencies
  187. Microsoft.EntityFrameworkCore.Query.QueryTranslationPreprocessorDependencies
  188. Microsoft.EntityFrameworkCore.Query.QueryTranslationPostprocessorDependencies
  189. Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitorDependencies
  190. Microsoft.EntityFrameworkCore.ValueGeneration.ValueGeneratorSelectorDependencies
  191. Microsoft.EntityFrameworkCore.Storage.DatabaseDependencies
  192. Microsoft.EntityFrameworkCore.Infrastructure.ModelDependencies
  193. Microsoft.EntityFrameworkCore.ModelCreationDependencies
  194. Microsoft.EntityFrameworkCore.Metadata.AdHocMapperDependencies
复制代码
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。
  1. public class Blog
  2. {
  3.     // 私有字段
  4.     private <strong>IEntityType? _thisEntity;
  5. </strong>    // 私有构造器
  6.     private Blog(IEntityType t) => _thisEntity = t;
  8.     // 公共构造器
  9.     public Blog()
  10.     {
  11.     }
  13.     public int BlogID { get; set; }
  14.     public string DisplayName { get; set; } = string.Empty;
  15.     public string Url { get; set; } = string.Empty;
  17.     public List<Post> PostList { get; set; } = new();
  19.     // 以下属性通过注入的 IEntityType 获取相关值
  20.     public int PropertyCount => _thisEntity?.GetProperties().Count() ?? 0;
  21.     public int NavigationCount => _thisEntity?.GetNavigations().Count() ?? 0;
  22.     public int KeyCount => _thisEntity?.GetKeys().Count() ?? 0;
  23. }
  25. public class Post
  26. {
  27.     public int PostID { get; set; }
  28.     public string Header { get; set; } = string.Empty;
  29.     public Blog? TheBlog { get; set; }
  30. }
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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。
  1. var q = c.Blogs.Include(b => b.PostList).ToArray();
  2. var first = q.FirstOrDefault();
  3. if (first != null)
  4. {
  5.     Console.WriteLine($"实体{first.GetType().Name}有{first.
  6. PropertyCount}个属性，{first.KeyCount}个键，{first.
  7. NavigationCount}个导航属性");
  8. }
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得到的输出如下：
  1. 实体Blog有3个属性，1个键，1个导航属性
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除了构造函数，也可以从属性注入。例如
  1. [PrimaryKey(nameof(Screen.ScrID))]
  2. public class Screen
  3. {
  4.     [Column("scr_id")]
  5.     public int ScrID { get; set; }
  6.     [Column("width")]
  7.     public int Width { get; set; }
  8.     [Column("height")]
  9.     public int Height { get; set; }
  11.     //----------- 注意以下属性 --------------
  12.     public <strong>MyDBContext? ThisContext</strong> { get; set; }
  13. }
  15. public class MyDBContext : DbContext
  16. {
  17.     public MyDBContext(DbContextOptions<MyDBContext> options)
  18.         : base(options)
  19.     { }
  20.         
  21.     public DbSet<Screen> Screens { get; set; }
  22. }
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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。
  1. var q = dc.Screens.FirstOrDefault();
  2. if (q != null)
  3. {
  4.     if (q.ThisContext != null)
  5.     {
  6.         Console.WriteLine("ThisContext属性：{0}", q.ThisContext);
  7.     }
  8. }
  10. // 输出：
  11. // ThisContext属性：MyDBContext
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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。
 

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