In this article I will tell how to build "Related Reads" section for a gatsby blog, like the one you can find at the bottom of this page.
As a prerequisite I expect, that you are already familiar with gatsby or even have an app with some source [-plugin]where you pull your articles from.
I use netlify cms and store all my articles next to the source code in git as markdown files. So gatsby-source-filesystem and gatsby-transformer-remark plugins are responsible for making them available in graphql. E.g. here is how I can query all articles:
query BlogPostList {
allMarkdownRemark {
nodes {
frontmatter {
title
}
}
}
}
But enough about me, let's get back to business.
Setup local plugin
First of all, I want to implement this feature as a local plugin (instead of root gatsby-node.js). I find this approach more idiomatic and clear. Creating one is a piece of cake and gatsby has a decent documentation about it, so check it out if you haven't yet.
As a result, we should have /plugins/related-reads/gatsby-node.js along with empty package.json and name (equal to name of the folder!) of our plugin listed in gatsby-config.js.
Extend graphql
The next step would be extending graphql schema, generated by gatsby-transformer-remark. So along with a content of an article, we can also request a list of articles about similar topic[s]. Like this:
query BlogPostList {
allMarkdownRemark {
nodes {
frontmatter {
title
}
// highlight-start
relatedReads {
slug
title
}
// highlight-end
}
}
}
A while ego gatsby team provided very nice way to achieve this - schema customization API. And we are going to leverage it, particularly createResolvers:
exports.createResolvers = ({ createResolvers }) =>
createResolvers({
// node type we want to extend
MarkdownRemark: {
// name of the field we want to add
relatedReads: {
// we return an array of other articles
type: '[MarkdownRemark!]',
// let's allow to specify number of articles returned
args: { limit: 'Int' },
async resolve(
source, // the node we extend
args,
// collection of helpers
// including access to internal store - nodeModel
ctx
) {
return []
},
},
},
})
No we can implement the last bit - the logic of Relative Reads. In my blog each post have a list of tags, so I gonna use it to measure similarity.
const intersection = require('lodash.intersection')
// I've extracted the resolve function just to get rid of extra noise
let resolve = async (source, args, ctx) {
let { frontmatter: { slug, lang, tags } } = source
let { limit = Number.MAX_SAFE_INTEGER } = args
// request all other posts
let otherPosts = await ctx.nodeModel.runQuery({
firstOnly: false, // we want to get an array
type: 'MarkdownRemark',
query: {
filter: {
frontmatter: {
slug: { ne: slug }, // not current article or translation
lang: { eq: lang }, // same lang
},
},
},
})
return otherPosts
.map((p) => ({
...p,
// measure the similarity by the size of tags intersection
similarity: intersection(p.frontmatter.tags, tags).length,
}))
.filter(({ similarity }) => similarity !== 0)
.sort(
(a, b) =>
b.similarity - a.similarity ||
b.frontmatter.date.localeCompare(a.frontmatter.date)
)
.slice(0, limit)
}
That is it! Pretty easy implementation and zero runtime cost - everything is requested ahead of time and build into your html pages, that is the strongest point if gatsby and JAMStack.
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