Using GROQ query result value in another query for filtering

Based on your use case of getting the next blog post after a certain date, you'll want to use the value from your first query as a parameter in your second query. Here's how to approach this:

Basic Approach

First, fetch the current blog post and extract the date:

const currentPost = await sanityClient.fetch(
  `*[_type == "post" && slug.current == $slug][0]{
    title,
    publishedDate
  }`,
  { slug: "my-post-slug" }
)

Then use that date as a parameter in your second query to get the next post:

const nextPost = await sanityClient.fetch(
  `*[_type == "post" && publishedDate > $date] | order(publishedDate asc)[0]`,
  { date: currentPost.publishedDate }
)

More Efficient: Single Query Approach

However, you can actually accomplish this more efficiently with a single query that gets both the current post and the next post. Here's how:

const result = await sanityClient.fetch(
  `*[_type == "post" && slug.current == $slug][0]{
    title,
    publishedDate,
    "nextPost": *[_type == "post" && publishedDate > ^.publishedDate] | order(publishedDate asc)[0]{
      title,
      slug
    }
  }`,
  { slug: "my-post-slug" }
)

The ^ operator references the parent document's field, so ^.publishedDate refers to the current post's date while you're filtering for the next post.

Key Points

As covered in the GROQ Parameters documentation, parameters are passed using the $ syntax and must be JSON literals. This approach is much safer than string concatenation and prevents GROQ injection attacks.

The single-query approach is generally preferable because it:

• Reduces API calls (better performance and lower costs)
• Ensures data consistency (both results from the same point in time)
• Simplifies your code

If you need to get both the previous and next posts, you can extend the single query:

*[_type == "post" && slug.current == $slug][0]{
  title,
  publishedDate,
  "nextPost": *[_type == "post" && publishedDate > ^.publishedDate] | order(publishedDate asc)[0],
  "previousPost": *[_type == "post" && publishedDate < ^.publishedDate] | order(publishedDate desc)[0]
}