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Troubleshooting undefined data in Next.js and Sanity integration

17 replies
Last updated: Jul 6, 2022
Hello,can anyone tell me how could I get the data (during console.log) I am getting undefined in my [slug.js file] this is my code

const myquery = `*[_type == "post"] {
    title,
    _id,
    mainImage,
   body
    }`

export const Post = ({posts, title, image}) => {

    console.log(posts, title, image);
    return (
        <div>
        <h1>Post</h1>
        </div>
    );
};

export const getServersideprops = async () => {
    const result = await client.fetch(myquery)
    return {
        props: {
            title: result.title,
            posts: result.body,
            image: result.mainImage,
        }
    }
}
AI Update

I can see the issue in your code! There are actually two problems causing the undefined values:

1. Typo in function name

You wrote getServersideprops but it should be getServerSideProps (capital S in Server and capital P in Props). Next.js won't recognize your function with the incorrect casing, so it won't execute at all, leaving your props undefined.

2. Incorrect data structure handling

Your client.fetch(myquery) returns an array of posts (because of the *[_type == "post"] query), but you're treating it like a single object. You're trying to access result.title directly, but result is an array, not an object.

Here's the corrected code:

const myquery = `*[_type == "post"] {
    title,
    _id,
    mainImage,
    body
}`

export default function Post({posts}) {
    console.log(posts); // This will now show your array of posts
    return (
        <div>
            <h1>Post</h1>
            {posts && posts.map(post => (
                <div key={post._id}>
                    <h2>{post.title}</h2>
                </div>
            ))}
        </div>
    );
}

export const getServerSideProps = async () => {
    const result = await client.fetch(myquery)
    return {
        props: {
            posts: result, // result is already the array of posts
        }
    }
}

If you want to fetch a single post (which seems likely since this is a [slug].js file), you should modify your query to filter by the slug parameter:

export const getServerSideProps = async (context) => {
    const { slug } = context.params;
    
    const query = `*[_type == "post" && slug.current == $slug][0] {
        title,
        _id,
        mainImage,
        body
    }`
    
    const post = await client.fetch(query, { slug })
    
    return {
        props: {
            post, // Now this is a single post object
        }
    }
}

export default function Post({post}) {
    console.log(post); // Will show your single post
    return (
        <div>
            <h1>{post?.title}</h1>
        </div>
    );
}

The key differences:

  • Fixed the function name capitalization
  • Used context.params to get the slug from the URL
  • Added a filter && slug.current == $slug to get the specific post
  • Added [0] to get the first (and only) result instead of an array
  • Passed the slug as a parameter using GROQ parameters to prevent GROQ injection

This should resolve your undefined issues!

Your function needs to be 
getServerSideProps()
. The capitalization is important.
Ya mybad I did but still undefinedcan I get a code snippet from where I can find how to properly fetch the data from the sanity??
You should use a default export for your component, not a named export. Next.js cannot guess what your component is called. 🙂
Hello ma'am I tried with the export default still my console is showing undefined below is my code snippet
import Head from 'next/head'
import Image from 'next/image'
import {sanityClient, urlFor} from '../sanity';



export default function Home({posts}) {

    console.log(posts);

  return (
    <h1>Welcome</h1>
  );
}


export const getServerSideprops = async () => {
  const query = `*[_type == "post"] {
    title,
    _id,
    mainImage,
    body
    }`
  const posts = await sanityClient.fetch(query)
  return {
    props: {
      posts,
    }
  }
}
and this is my sanity.js file
import {
    createClient,
    createPortableTextComponent,
    createImageUrlBuilder,
    createPreviewSubscriptionHook
  } from "next-sanity";

export const config = {
    /**
     * Find your project ID and dataset in `sanity.json` in your studio project.
     * These are considered "public", but you can use environment variables
     * if you want differ between local dev and production.
     *
     * <https://nextjs.org/docs/basic-features/environment-variables>
     **/
    dataset: process.env.NEXT_PUBLIC_SANITY_DATASET || "production",
    projectId: process.env.NEXT_PUBLIC_SANITY_PROJECT_ID,
    apiVersion: "2021-08-11", // or today's date for latest
    /**
     * Set useCdn to `false` if your application require the freshest possible
     * data always (potentially slightly slower and a bit more expensive).
     * Authenticated request (like preview) will always bypass the CDN
     **/
    useCdn: process.env.NODE_ENV === "production",
  };

  // setup the client for fetching data in the getProps page functions
  export const sanityClient = createClient(config);

  export const urlFor = (source) =>
  createImageUrlBuilder(config).image(source);


// export const useCurrentUser = createCurrentUserHook(config);
Just double checking but: are you reaching the right page in the browser? 🙂
yes I am trying with the home page only
see I am getting the query but in next.js it is undefined
Oh, I know why. You’re querying an array of posts, not a single one — the query in Vision shows that as well. You need to add 
[0]
to your query if you want a single post, or you need to treat a collection (with a map or something).
I mean, a good way to check that your query works is to log the result of the actual query before you pass it down to your component. I think it would show you tht it works fine. 🙂
still undefined 🥲
I will define it by maps when I will get some json data but I am not getting anything
If you log 
result
right after the definition, it’s undefined?
Like this??
export const getServerSideprops = async () => {
  const query = `*[_type == "post"][0] {
    title,
    _id,
    mainImage,
    body
    }`
  const posts = await sanityClient.fetch(query);
  
  return {
    props: {
      posts,
    },
  }
  console.log({posts});
}
Before the return statement, otherwise it will not fire. 🙂
Also remember that 
[0]
in your query means you pick up the first post, so the variable probably shouldn’t be named 
posts
. 😉
And as
user A
stated above it is important to have the right kind of capitalisation in your functions:
⛔ getServerSideprops()
✅ get*S*erver*S*ide*P*rops()

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