Query referenced entries that are referenced elsewhere

Hi Kevin,

Currently, there is no direct way to obtain those result using the CDA API. However, one way you can achieve this is through the following two-step process:

1. Fetch blogs with at least one referenced category: First, get all the blogs that have at least one referenced category. The following query will filter out all the blogs that don't have any categories attached, using the $ne query. 

   https://cdn.contentstack.io/v3/content_types/blog/entries?environment=production&locale=en-us&query={"categories": { "$ne": [] }}&include_count=true

    

2. Extract unique category UIDs and fetch corresponding entries: Next, from the response, extract all the unique UIDs of the category entries. Then, make another API call to retrieve the entry data of the referred categories, using the $in query. 

   https://cdn.contentstack.io/v3/content_types/catagories/entries?environment=production&locale=en-us&include[]=categories&query={"uid": { "$in": ["blt630c4fc00bb50385"] }}

With this, you should be able to retrieve the categories that are referenced at least once. And here's an example of how these steps can be applied:

const response = {
    "entries": [
        {
            "_version": 1,
            "locale": "en-us",
            "uid": "blt03df3d2b38bdc18c",
            "ACL": {},
            "_in_progress": false,
            "categories": [
                {
                    "uid": "blt630c4fc00bb50385",
                    "_content_type_uid": "catagories"
                }
            ],
            "created_at": "2023-08-09T11:37:58.177Z",
            "created_by": "blt829fa9ec1c032475",
            "tags": [],
            "title": "blog2",
            "updated_at": "2023-08-09T11:37:58.177Z",
            "updated_by": "blt829fa9ec1c032475",
            "publish_details": {
                "environment": "blt6ec191271b8120df",
                "locale": "en-us",
                "time": "2023-08-09T11:38:00.424Z",
                "user": "blt829fa9ec1c032475"
            }
        },
        {
            "_version": 1,
            "locale": "en-us",
            "uid": "blt02b3f7da05d5834a",
            "ACL": {},
            "_in_progress": false,
            "categories": [
                {
                    "uid": "blt630c4fc00bb50385",
                    "_content_type_uid": "catagories"
                }
            ],
            "created_at": "2023-08-09T11:37:40.490Z",
            "created_by": "blt829fa9ec1c032475",
            "tags": [],
            "title": "Blog 1",
            "updated_at": "2023-08-09T11:37:40.490Z",
            "updated_by": "blt829fa9ec1c032475",
            "publish_details": {
                "environment": "blt6ec191271b8120df",
                "locale": "en-us",
                "time": "2023-08-09T11:37:42.633Z",
                "user": "blt829fa9ec1c032475"
            }
        }
    ],
    "count": 2
};
​
const uniqueCategoryUids = new Set();
​
response.entries.forEach(entry => {
    entry.categories.forEach(category => {
        uniqueCategoryUids.add(category.uid);
    });
});
​
const categoryUidsArray = Array.from(uniqueCategoryUids);
​
console.log(categoryUidsArray); // Output: ['blt630c4fc00bb50385']