How to Preserve Both [Required] and Nullable Properties in Swashbuckle Schema Output?

[Slys-cmd]

I have a DTO class defined as follows:

public class QuantityDto
{
    [Required]
    public decimal? Value { get; set; }

    [Required]
    public string? Unit { get; set; }
}

My goal is to maintain both the [Required] validation attribute (per project requirements) and the nullable property types in the generated OpenAPI/Swagger schema using Swashbuckle.

Currently, Swashbuckle produces the following output for this class:

"QuantityDto": {
    "required": [
      "unit",
      "value"
    ],
    "type": "object",
    "properties": {
      "value": {
        "type": "number",
        "format": "double"
      },
      "unit": {
        "minLength": 1,
        "type": "string"
      }
    },
    "additionalProperties": false
}

However, I need the schema to reflect the fact that these properties are nullable (for example, to indicate nullable: true), while retaining the required attribute for validation.

I understand that [Required] is typically not recommended with nullable types, but due to project constraints, I cannot change this approach.

Is there an option or workaround in Swashbuckle to generate a schema that marks properties as both required and nullable, or otherwise accurately represents this scenario?

I have tried reviewing the schema generation options and experimenting with custom schema filters, but haven’t found a suitable solution so far.

Any insight or recommended approach would be greatly appreciated!

[martincostello]

You could implement a filter to post-process the schema to make the edits you require.