How to express an array in a swagger definition

I'm almost there.

extension:
        type: array
        items:
          type: object
          properties:
            race:
              $ref: '#/definitions/Race'
            ethnicity:
              $ref: '#/definitions/Ethnicity'
            sex:
              $ref: '#/definitions/Sex'

This includes an extraneous key before each definition

  "extension": [{
    "race": {
      "url": "http://hl7.org/fhir/StructureDefinition/us-core-race",
      "extension": {
        "url": "ombCategory",
        "valueCoding": {
          "system": "http://hl7.org/fhir/v3/Race",
          "code": "2106-3",
          "display": "White"
        }
      }
    },
    "ethnicity": {
      "url": "http://hl7.org/fhir/StructureDefinition/us-core-ethnicity",
      "extension": {
        "url": "ombCategory",
        "valueCoding": {
          "system": "http://hl7.org/fhir/v3/Ethnicity",
          "code": "2135-2",
          "display": "Hispanic or Latino"
        }
      }
    },
    "sex": {
      "url": "http://hl7.org/fhir/StructureDefinition/us-core-birthsex",
      "valueCode": "M"
    }
  }]

But I need it to look like this:

"extension": [
    {
      "url": "http://hl7.org/fhir/StructureDefinition/us-core-race",
      "extension": {
        "url": "ombCategory",
        "valueCoding": {
          "system": "http://hl7.org/fhir/v3/Race",
          "code": "2106-3",
          "display": "White"
        }
      }
    },
    {
      "url": "http://hl7.org/fhir/StructureDefinition/us-core-ethnicity",
      "extension": {
        "url": "ombCategory",
        "valueCoding": {
          "system": "http://hl7.org/fhir/v3/Ethnicity",
          "code": "2135-2",
          "display": "Hispanic or Latino"
        }
      }
    },
    {
      "url": "http://hl7.org/fhir/StructureDefinition/us-core-birthsex",
      "valueCode": "M"
    }
  ]

Thanks RonRatovsky  for any additional help you might be able to offer.