How to decode polimorphic relations

[alexandru-calinoiu]

Given the following json

                            {
                                "data": {
                                    "id": "38",
                                    "type": "question_set",
                                    "attributes": {
                                        "position": 33,
                                        "title": "Goal 2: Zero Hunger"
                                    },
                                    "relationships": {
                                        "form_category": {
                                            "data": {
                                                "id": "6",
                                                "type": "form_category"
                                            }
                                        },
                                        "responses": {
                                            "data": []
                                        },
                                        "form_questions": {
                                            "data": [
                                                {
                                                    "id": "43",
                                                    "type": "text_area"
                                                },
                                                {
                                                    "id": "44",
                                                    "type": "text"
                                                }
                                            ]
                                        }
                                    },
                                    "links": {
                                        "self": "http://localhost:4000/v1/cops/1/questions/38",
                                        "next_question": "http://localhost:4000/v1/cops/1/questions/44",
                                        "prev_question": "http://localhost:4000/v1/cops/1/questions/32"
                                    }
                                },
                                "included": [
                                    {
                                        "id": "6",
                                        "type": "form_category",
                                        "attributes": {
                                            "position": 6,
                                            "title": "SDGs"
                                        },
                                        "relationships": {
                                            "form_questions": {
                                                "data": []
                                            }
                                        }
                                    },
                                    {
                                        "id": "43",
                                        "type": "text_area",
                                        "attributes": {
                                            "position": 4,
                                            "title": "Please use this space to describe in more detail the work you are undertaking to contribute to this Goal"
                                        },
                                        "relationships": {
                                            "form_category": {
                                                "data": {
                                                    "id": "6",
                                                    "type": "form_category"
                                                }
                                            },
                                            "responses": {
                                                "data": []
                                            }
                                        },
                                        "links": {
                                            "self": "http://localhost:4000/v1/forms/1/questions/43",
                                            "next_question": null,
                                            "prev_question": null
                                        }
                                    },
                                    {
                                        "id": "44",
                                        "type": "text",
                                        "attributes": {
                                            "position": 5,
                                            "title": "Other question type"
                                        },
                                        "relationships": {
                                            "form_category": {
                                                "data": {
                                                    "id": "6",
                                                    "type": "form_category"
                                                }
                                            },
                                            "responses": {
                                                "data": []
                                            }
                                        },
                                        "links": {
                                            "self": "http://localhost:4000/v1/forms/1/questions/44",
                                            "next_question": null,
                                            "prev_question": null
                                        }
                                    }
                                ]
                            }

How can I decode the form_questions relation? I need some way to access the type so I know what decoder to use.