Property annotations do not generate jsonschema if attributes exists on MetadataType buddy class

[JeffBarnard]

I am using ef-core database first tools (efpt) to generate portable POCO models. I am then extending these classes by adding metadata 'buddy classes' to annotate them for validation rules.

public partial class Model 
{
    public int Id { get; set; }
}

[MetadataType(typeof(ModelMeta))]   
public partial class Model
{
    public class ModelMeta
    {       
        [Range(2,5)]
        public int Id { get; set; }
    }
}

You can also use interfaces:

[MetadataType(typeof(IModelMeta))]   
public partial class Model : IModelMeta
{       
}

public interface IModelMeta
{
    [Range(2,5)]
    int Id { get; set; }
}

Annotations do not work and output the expected jsonschema. Here are some examples I've tried:

[Required]
[Range(2,5)]
[ReadOnly(true)]
[DefaultValue(typeof(int), "1")]

They do work if the annotations are on the original partial class definition, but I cannot do this since they are tool-generated.

Thanks for reading.

[JeffBarnard]

When using the .net ValidationContext to validate our objects, the metadata classes need to be registered in order for that api to detect them. I don't know why they require us to do this, but perhaps this is a useful reference:

foreach (MetadataTypeAttribute attrib in type.GetCustomAttributes(typeof(MetadataTypeAttribute), true))
{
    System.ComponentModel.TypeDescriptor.AddProviderTransparent(
        new AssociatedMetadataTypeTypeDescriptionProvider(type, attrib.MetadataClassType), type);
}

[JeffBarnard]

We've worked around this issue by simply writing code to detect the attributes and applying/mapping them to the schema manually. This means we must maintain our own list of supported attributes so it's not great.

Edited for brevity:

public static void ApplyMetadataToJson(JsonSchema schema, Type type)
{
    var metadataType = type.GetCustomAttribute<MetadataTypeAttribute>()?.MetadataClassType;
    var properties = metadataType?.GetProperties();
    foreach (var property in properties)
    {
        var attributes = property.GetCustomAttributes(true);
        var schemaProperty = schema.Properties[property.Name];

        foreach (var attribute in attributes)
        {
            switch (attribute)
            {
                case RequiredAttribute requiredAtrribute:
                    schemaProperty.IsRequired = true;
                    break;                          
                case DescriptionAttribute descriptionAttribute:
                    schemaProperty.Description = descriptionAttribute.Description;
                    break;
               ...
            }
        }        
    }
}