How to access forgin key value in react from django api

I have django api in which i have post model which is linked to comments and categories table by forgin key now i am feching data for post detail and when i try to access category of that post it return s id and i want to access name of category this is my post list view

{
        "id": 4,
        "title": "BLOG PAGE",
        "body": "testing",
        "owner": "ankit",
        "comments": [],
        "categories": [
            2
        ],
        "created_at": "2021-05-07T17:22:32.989706Z"
    },
    {
        "id": 5,
        "title": "Test Post",
        "body": "This is a test Post",
        "owner": "ankit",
        "comments": [],
        "categories": [
            2
        ],

and this is my categories

[
    {
        "id": 2,
        "name": "Python",
        "owner": "ankit",
        "posts": [
            4,
            5,
            6,
            8
        ]
    }
]

and this is my post detail component

export class PostDetail extends React.Component {
  
  constructor(props) {
    super(props);
    const ID = this.props.match.params.id
    this.state = {
      data: [],
      loaded: false,
      placeholder: "Loading"
    };
  }

  formatDate(dateString){
      const options = { year: "numeric", month: "long", day: "numeric" }
      return new Date(dateString).toLocaleDateString(undefined, options)
  }

    componentDidMount() {
    fetch(`${Url}posts/${this.props.match.params.id}`)
      .then(response => {
        if (response.status > 400) {
          return this.setState(() => {
            return { placeholder: "Something went wrong!" };
          });
        }
        return response.json();
      })

      .then(data => {
        this.setState(() => {
          return {
            data,
            loaded: true
          };
        });
      });
  }

  render(){
    return(
      <>
      <h1 className="main-title">{this.state.data.title}</h1>
      <div className="container">
        <div className="box1">
          <h2>Categories</h2>
          <div className="categories">{this.state.data.categories}</div>
        </div>
      </>
      );
  }
}

and i am getting output as 2 when i try to get data like mention above i thought i can access it by putting . in front of categories eg. categories.name but it returns TypeError error

TypeError: Cannot read property 'name' of undefined

this are my serializers

class CategorySerializer(serializers.ModelSerializer):
    owner = serializers.ReadOnlyField(source='owner.username')
    posts = serializers.PrimaryKeyRelatedField(many=True, read_only=True)

    class Meta:
        model = Category
        fields = ['id', 'name', 'owner', 'posts']


class PostSerializer(serializers.ModelSerializer):
    owner = serializers.ReadOnlyField(source='owner.username')
    comments = serializers.PrimaryKeyRelatedField(many=True, read_only=True)

    class Meta:
        model = Post
        fields = ['id', 'title', 'body', 'owner', 'comments', 'categories','created_at']