Is It possible to query post within the same category in frontmatter?

[sparklesam]

Summary

I'm trying to show related post under the same frontmatter categories. Is it possible to do this within a GraphQL query?

In page template for blog post, I have already setup another query for frontmatter categories, just dunno how to connect two queries together.

  query BlogPostBySlug($slug: String!) {
    post: markdownRemark(fields: { slug: { eq: $slug } }) {
      html
      timeToRead
      excerpt
      frontmatter {
        title
        cover
        date
        category
        tags
      }
      fields {
        nextTitle
        nextSlug
        prevTitle
        prevSlug
        slug
        date
      }
    }
    related: allMarkdownRemark(
      filter: {
        frontmatter: {
          category: {
             eq: { ???} 
          }
        }
      }
    ) {
       edges {
          node {
             id
            frontmatter {
              title
            }
            }
          }
        }
  }

File contents (if changed)

  System:
    OS: macOS 10.14.2
    CPU: x64 Intel(R) Core(TM) i5-7267U CPU @ 3.10GHz
    Shell: 3.2.57 - /bin/bash
  Binaries:
    Node: 10.8.0 - /usr/local/bin/node
    npm: 6.2.0 - /usr/local/bin/npm
  Browsers:
    Chrome: 71.0.3578.98
    Firefox: 65.0
    Safari: 12.0.2
  npmPackages:
    gatsby: 2.0.40 => 2.0.40
    gatsby-image: 2.0.19 => 2.0.19
    gatsby-plugin-catch-links: 2.0.6 => 2.0.6
    gatsby-plugin-feed: 2.0.9 => 2.0.9
    gatsby-plugin-google-analytics: 2.0.7 => 2.0.7
    gatsby-plugin-lodash: 3.0.2 => 3.0.2
    gatsby-plugin-manifest: 2.0.7 => 2.0.7
    gatsby-plugin-nprogress: 2.0.6 => 2.0.6
    gatsby-plugin-offline: 2.0.12 => 2.0.12
    gatsby-plugin-react-helmet: 3.0.1 => 3.0.1
    gatsby-plugin-sharp: 2.0.12 => 2.0.12
    gatsby-plugin-sitemap: 2.0.2 => 2.0.2
    gatsby-plugin-styled-components: ^3.0.4 => 3.0.4
    gatsby-plugin-twitter: 2.0.7 => 2.0.7
    gatsby-plugin-web-font-loader: ^1.0.4 => 1.0.4
    gatsby-remark-autolink-headers: 2.0.10 => 2.0.10
    gatsby-remark-copy-linked-files: 2.0.6 => 2.0.6
    gatsby-remark-images: 2.0.6 => 2.0.6
    gatsby-remark-prismjs: 3.0.3 => 3.0.3
    gatsby-remark-responsive-iframe: 2.0.6 => 2.0.6
    gatsby-source-filesystem: 2.0.7 => 2.0.7
    gatsby-transformer-remark: 2.1.11 => 2.1.11
    gatsby-transformer-sharp: 2.1.8 => 2.1.8
  npmGlobalPackages:
    gatsby-cli: 1.1.58

gatsby-config.js: N/A
package.json: N/A
gatsby-node.js: N/A
gatsby-browser.js: N/A
gatsby-ssr.js: N/A

[pieh]

You can pass category alongside slug in gatsby-node when you use createPages, then you could use adjust query to use it:
query BlogPostBySlug($slug: String!, $category: String!) { and eq: $category

[sparklesam]

Thanks a lot! I have added category: edge.node.frontmatter.category, in the context for createPage. But I was also wondering, how could i add an except condition to avoid duplicate on current article?

query BlogPostBySlug($slug: String!, $category: String!) {
  post: markdownRemark(fields: {slug: {eq: $slug}}) {
    html
    timeToRead
    excerpt
    frontmatter {
      title
      cover
      date
      category
      tags
    }
    fields {
      nextTitle
      nextSlug
      prevTitle
      prevSlug
      slug
      date
    }
  }
  related: allMarkdownRemark(sort: {fields: [fields___date], order: DESC},limit: 3, filter: {frontmatter: {category: {eq: $category}}}) {
    edges {
      node {
        frontmatter {
          title
        }
        fields {
          slug
        }
      }
    }
  }
}

[sidharthachatterjee]

@sparklesam You could add another filter that does a not equal check with the current slug

So then the filter section becomes

filter: {
  frontmatter: {
    category: {
      eq: $category
    }
  },
  fields: {
    slug: {
      ne: $slug
    }
  }
}

[sparklesam]

Thanks a lot for all your help!