firebase POST url 400 bad request

Question

I am trying to use a very simple method to post requests to firebase realtime DB from my reactjs app. Here is a screenshot of a one entry into my DB . Here the first entry under blogs is the UID of the user and that user can create multiple blogs for example with id b1 in the screenshot.

Here is my code for the POST request:

const id = localStorage.getItem('uid')
 const postData = async () => {
        var num = localStorage.getItem('blogNumber')
        const resp = await fetch(
            'https://assignment-c3557-default-rtdb.asia-southeast1.firebasedatabase.app.firebaseio.com/blogs.json',
            {
             method: 'POST',
             body: {
                id: {
                    num : {
                        title: titleRef.current.value,
                        description: contentRef.current.value,
                        createdAt: new Date(),
                        isPosted: false
                    }
                }
            },
            headers: {
                'Content-Type': 'application/json'
            }
            });
            const data = await resp.json()
           localStorage.setItem('blogNumber', localStorage.getItem('blogNumber') +1)
    }

I get 400 bad request when trying to hit this url

But according to this page, this seems to be the correct url I am hitting

https://retool.com/blog/your-guide-to-crud-in-firebase-realtimedb-with-rest-api/

Answer 1

There are a number of things wrong here:

• You aren't using the value of id or num here, you need to wrap them in square brackets
• The body property of a fetch API call should be passed through JSON.stringify .
• You shouldn't post a Date object in the body of a request. Either convert it to a string, convert it to a plain number, use a timestamp object or use a server value placeholder.
• Your code always assumes that the post was created successfully. The fetch API will not throw an error for bad status codes. You should check the status code to determine what you want to do. As Firebase Database operations usually respond in JSON, I've parsed the body here as JSON before checking the code however you should probably check for empty bodies first.
• Using POST /blogs.json will overwrite your entire /blogs tree each time you write data. You should change the path or use a PATCH request with the proper body for it.

const id = localStorage.getItem('uid')
const postData = async () => {
  const num = localStorage.getItem('blogNumber')
  const reqData = {
    [id]: { // <-- use square brackets for value as key
      [num]: { // <-- use square brackets for value as key
        title: titleRef.current.value,
        description: contentRef.current.value,
        createdAt: Date.now(), // <-- returns milliseconds since epoch
        isPosted: false
      }
    }
  }

  const resp = await fetch(
    'https://assignment-c3557-default-rtdb.asia-southeast1.firebasedatabase.app.firebaseio.com/blogs.json',
    {
      method: 'POST',
      body: JSON.stringify(reqData), // you need to stringify this yourself
      headers: {
        'Content-Type': 'application/json'
      }
    }
  );

  
  const data = await resp.json();

  if (!resp.ok) { // fetch API does not throw errors by itself
    const err = new Error('Unexpected status: ' + resp.status);
    err.data = data;
    err.resp = resp;
    throw err;
  }

  localStorage.setItem('blogNumber', localStorage.getItem('blogNumber')+1)
}

Updated to use deeper path:

const id = localStorage.getItem('uid')
const postData = async () => {
  const num = localStorage.getItem('blogNumber')
  const reqData = {
    title: titleRef.current.value,
    description: contentRef.current.value,
    createdAt: Date.now(), // <-- returns milliseconds since epoch
    isPosted: false
  }

  const resp = await fetch(
    `https://assignment-c3557-default-rtdb.asia-southeast1.firebasedatabase.app.firebaseio.com/blogs/${uid}/${num}.json`,
    {
      method: 'POST',
      body: JSON.stringify(reqData), // you need to stringify this yourself
      headers: {
        'Content-Type': 'application/json'
      }
    }
  );
  
  const data = await resp.json();

  if (!resp.ok) { // fetch API does not throw errors by itself
    const err = new Error('Unexpected status: ' + resp.status);
    err.data = data;
    err.response = resp;
    throw err;
  }

  localStorage.setItem('blogNumber', localStorage.getItem('blogNumber')+1)
}