带包装键的复杂json到swift结构

JSON文件

{
    "title": "this is a title",
    "children": {
        "attachment": {
            "results": [
                {
                    "id": "att241845336",
                    "metadata": {
                        "mediaType": "application/vnd.ms-excel.sheet.macroEnabled.12"
                    },
                    "extensions": {
                        "fileSize": 430395,
                    }
                },
                {
                    "id": "att241844542",
                    "metadata": {
                        "mediaType": "image/png"
                    },
                    "extensions": {
                        "fileSize": 114781,
                    }
                }
            ],
            "size": 25,
        },
        "_links": {
            "self": "https://example.com/rest/api/content/241845389/child"
        },
        "_expandable": {
            "comment": "/rest/api/content/241845389/child/comment",
            "page": "/rest/api/content/241845389/child/page"
        }
    },
    "_links": {
        "collection": "/rest/api/content",
    }
}

struct MetaMessage : Codable {
    struct Message : Codable {
        let title: String
        let children: [child]
        let _links: [link]
    }

    struct child {
        let attachment: [attachments]
        let _links: [link]
        let _expandable: [expandables]
    }

        struct attachments {
            let results: [result]
            let size: int
        }

            struct result {
                let id: String
                let metadata: [metadataSub]
                let extensions: [extension]
            }

                struct metadataSub {
                    let mediaType: Sting
                }

                struct extension {
                    let fileSize: Long
                }

        struct link {
            let self: URL
        }

        struct expandables {
            let comment: String
            let page: String
        }

    struct expandables {
        let collection: String
    }
}