【EF Core】实体类的依赖注入

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.         };

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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. }

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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

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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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