Discover IDBContextFactory at design-time

Fixes #21257

src/EFCore.Design/Design/Internal/DbContextOperations.cs

@@ -180,6 +180,7 @@ where i.IsGenericType
                 contexts.Add(
                     context,
                     FindContextFactory(context)
+                    ?? FindContextFromRuntimeDbContextFactory(appServices, context)
                     ?? (() => (DbContext)ActivatorUtilities.GetServiceOrCreateInstance(appServices, context)));
             }
 
@@ -188,13 +189,15 @@ where i.IsGenericType
             var types = _startupAssembly.GetConstructibleTypes()
                 .Concat(_assembly.GetConstructibleTypes())
                 .ToList();
+
             var contextTypes = types.Where(t => typeof(DbContext).IsAssignableFrom(t)).Select(
                     t => t.AsType())
                 .Concat(
                     types.Where(t => typeof(Migration).IsAssignableFrom(t))
                         .Select(t => t.GetCustomAttribute<DbContextAttribute>()?.ContextType)
                         .Where(t => t != null))
                 .Distinct();
+
             foreach (var context in contextTypes.Where(c => !contexts.ContainsKey(c)))
             {
                 _reporter.WriteVerbose(DesignStrings.FoundDbContext(context.ShortDisplayName()));
@@ -254,6 +257,17 @@ public virtual ContextInfo GetContextInfo([CanBeNull] string contextType)
             return info;
         }
 
+        private Func<DbContext> FindContextFromRuntimeDbContextFactory(IServiceProvider appServices, Type contextType)
+        {
+            var factoryInterface = typeof(IDbContextFactory<>).MakeGenericType(contextType);
+            var service = appServices.GetService(factoryInterface);
+            return service == null
+                ? (Func<DbContext>)null
+                : () => (DbContext)factoryInterface
+                    .GetMethod(nameof(IDbContextFactory<DbContext>.CreateDbContext))
+                    ?.Invoke(service, null);
+        }
+
         private Func<DbContext> FindContextFactory(Type contextType)
         {
             var factoryInterface = typeof(IDesignTimeDbContextFactory<>).MakeGenericType(contextType);

test/EFCore.Design.Tests/Design/Internal/DbContextOperationsTest.cs

@@ -24,6 +24,12 @@ public void CreateContext_gets_service_without_AddDbContext()
             CreateOperations(typeof(TestProgramWithoutAddDbContext)).CreateContext(typeof(TestContext).FullName);
         }
 
+        [ConditionalFact]
+        public void CreateContext_gets_service_when_context_factory_used()
+        {
+            CreateOperations(typeof(TestProgramWithContextFactory)).CreateContext(typeof(TestContextFromFactory).FullName);
+        }
+
         [ConditionalFact]
         public void Can_pass_null_args()
         {
@@ -119,6 +125,15 @@ private static TestWebHost BuildWebHost(string[] args)
                         .BuildServiceProvider());
         }
 
+        private static class TestProgramWithContextFactory
+        {
+            private static TestWebHost BuildWebHost(string[] args)
+                => new TestWebHost(
+                    new ServiceCollection()
+                        .AddDbContextFactory<TestContextFromFactory>(b => b.UseInMemoryDatabase("In-memory test database"))
+                        .BuildServiceProvider());
+        }
+
         private static class TestProgramRelational
         {
             private static TestWebHost BuildWebHost(string[] args)
@@ -163,6 +178,19 @@ public TestContext(DbContextOptions<TestContext> options)
             }
         }
 
+        private class TestContextFromFactory : DbContext
+        {
+            private TestContextFromFactory()
+            {
+                throw new Exception("This isn't the constructor you're looking for.");
+            }
+
+            public TestContextFromFactory(DbContextOptions<TestContextFromFactory> options)
+                : base(options)
+            {
+            }
+        }
+
         private class BaseContext : DbContext
         {
             public BaseContext(string factoryUsed)