Make GetContainerColumnType() always return the expected type

src/EFCore.Design/Migrations/Design/CSharpSnapshotGenerator.cs

@@ -707,8 +707,7 @@ protected virtual void GenerateComplexPropertyAnnotations(
         if (typeAnnotations.ContainsKey(RelationalAnnotationNames.ContainerColumnName)
             && !typeAnnotations.ContainsKey(RelationalAnnotationNames.ContainerColumnType))
         {
-            var containerColumnType = property.ComplexType.GetContainerColumnType()
-                ?? Dependencies.RelationalTypeMappingSource.FindMapping(typeof(JsonTypePlaceholder))?.StoreType;
+            var containerColumnType = property.ComplexType.GetContainerColumnType();
             if (containerColumnType != null)
             {
                 typeAnnotations[RelationalAnnotationNames.ContainerColumnType] = new Annotation(
@@ -921,8 +920,7 @@ protected virtual void GenerateEntityTypeAnnotations(
         if (annotations.ContainsKey(RelationalAnnotationNames.ContainerColumnName)
             && !annotations.ContainsKey(RelationalAnnotationNames.ContainerColumnType))
         {
-            var containerColumnType = entityType.GetContainerColumnType()
-                ?? Dependencies.RelationalTypeMappingSource.FindMapping(typeof(JsonTypePlaceholder))?.StoreType;
+            var containerColumnType = entityType.GetContainerColumnType();
             if (containerColumnType != null)
             {
                 annotations[RelationalAnnotationNames.ContainerColumnType] = new Annotation(

src/EFCore.Relational/Extensions/RelationalTypeBaseExtensions.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using Microsoft.EntityFrameworkCore.Internal;
+using Microsoft.EntityFrameworkCore.Metadata.Internal;
 
 // ReSharper disable once CheckNamespace
 #pragma warning disable IDE0130 // Namespace does not match folder structure
@@ -416,11 +417,32 @@ public static void SetContainerColumnName(this IMutableTypeBase typeBase, string
     /// <param name="typeBase">The type.</param>
     /// <returns>The database column type.</returns>
     public static string? GetContainerColumnType(this IReadOnlyTypeBase typeBase)
-        => typeBase.FindAnnotation(RelationalAnnotationNames.ContainerColumnType)?.Value is string columnName
-            ? columnName
-            : typeBase is IReadOnlyEntityType entityType
-                ? entityType.FindOwnership()?.PrincipalEntityType.GetContainerColumnType()
-                : ((IReadOnlyComplexType)typeBase).ComplexProperty.DeclaringType.GetContainerColumnType();
+    {
+        if (typeBase.FindAnnotation(RelationalAnnotationNames.ContainerColumnType)?.Value is string columnType)
+        {
+            return columnType;
+        }
+
+        var parentType = typeBase is IReadOnlyEntityType entityType
+            ? entityType.FindOwnership()?.PrincipalEntityType.GetContainerColumnType()
+            : ((IReadOnlyComplexType)typeBase).ComplexProperty.DeclaringType.GetContainerColumnType();
+
+        if (parentType != null)
+        {
+            return parentType;
+        }
+
+        if (typeBase.IsMappedToJson()
+#pragma warning disable EF1001 // Internal EF Core API usage.
+            && (typeBase.Model is not Model model || model.IsReadOnly))
+#pragma warning restore EF1001 // Internal EF Core API usage.
+        {
+            return ((IRelationalTypeMappingSource)((IModel)typeBase.Model).GetModelDependencies().TypeMappingSource)
+                .FindMapping(typeof(JsonTypePlaceholder))?.StoreType;
+        }
+
+        return null;
+    }
 
     /// <summary>
     ///     Sets the type of the container column to which the type is mapped.

test/EFCore.Relational.Tests/Metadata/RelationalModelTest.cs

@@ -3053,6 +3053,60 @@ public void Complex_collection_container_column_type_is_used_in_relational_model
             Assert.Equal("some_json_mapping", column.StoreType);
         }
 
+        [ConditionalFact]
+        public void Complex_property_gets_default_container_column_type_when_not_set_explicitly()
+        {
+            var modelBuilder = CreateConventionModelBuilder();
+
+            modelBuilder.Entity<EntityWithComplexProperty>(eb =>
+            {
+                eb.ComplexProperty(
+                    e => e.ComplexProperty, cb =>
+                    {
+                        cb.ToJson("complex_data");
+                    });
+            });
+
+            var model = Finalize(modelBuilder);
+
+            var entityType = model.Model.FindEntityType(typeof(EntityWithComplexProperty));
+            var complexProperty = entityType.GetComplexProperties().Single();
+            var complexType = complexProperty.ComplexType;
+
+            Assert.Equal("some_json_mapping", complexType.GetContainerColumnType());
+
+            var table = entityType.GetTableMappings().Single().Table;
+            var column = table.Columns.Single(c => c.Name == "complex_data");
+            Assert.Equal("some_json_mapping", column.StoreType);
+        }
+
+        [ConditionalFact]
+        public void Complex_collection_gets_default_container_column_type_when_not_set_explicitly()
+        {
+            var modelBuilder = CreateConventionModelBuilder();
+
+            modelBuilder.Entity<EntityWithComplexCollection>(eb =>
+            {
+                eb.ComplexCollection(
+                    e => e.ComplexCollection, cb =>
+                    {
+                        cb.ToJson("collection_data");
+                    });
+            });
+
+            var model = Finalize(modelBuilder);
+
+            var entityType = model.Model.FindEntityType(typeof(EntityWithComplexCollection));
+            var complexProperty = entityType.GetComplexProperties().Single();
+            var complexType = complexProperty.ComplexType;
+
+            Assert.Equal("some_json_mapping", complexType.GetContainerColumnType());
+
+            var table = entityType.GetTableMappings().Single().Table;
+            var column = table.Columns.Single(c => c.Name == "collection_data");
+            Assert.Equal("some_json_mapping", column.StoreType);
+        }
+
         [ConditionalFact]
         public void Can_use_relational_model_with_functions()
         {