queries

export const getSuggestedPostsByTagsQuery = `{
    "similarPosts": *[_type == "post" && slug.current != $slug && $tags in tags[].tag] | order(date desc, _updatedAt desc) [0...2] {
      ${postFields}
    }
  }`;

request.js

  const { similarPosts } = await getClient(preview).fetch(
    getSuggestedPostsByTagsQuery,
    {
      slug: params.slug,
      tags: post.tags.map((tag) => tag.tag),
    }
  );

schema.js

// tag
// post -- line 19

export const tag = {
  name: "tag",
  title: "Tag",
  type: "document",
  fields: [
    {
      name: "tag",
      title: "Tag",
      type: "string",
      validation: (Rule) => Rule.required(),
    },
  ],
};


export const post = {
  name: "post",
  title: "Post",
  type: "document",
  fields: [
    {
      name: "title",
      title: "Title",
      type: "string",
      validation: (Rule) => Rule.required(),
    },
    {
      name: "slug",
      title: "Slug",
      type: "slug",
      options: {
        source: "title",
        maxLength: 96,
      },
      validation: (Rule) => Rule.required(),
    },
    {
      name: "content",
      title: "Content",
      type: "array",
      of: [
        {
          type: "block",
          marks: {
            annotations: [
              {
                name: "footnote",
                type: "object",
                title: "Footnote",
                fields: [
                  {
                    name: "text",
                    type: "array",
                    of: [{ type: "block" }],
                  },
                ],
              },
            ],
          },
          lists: [
            { title: "Bullet", value: "bullet" },
            { title: "Numbered", value: "number" },
          ], // yes please, both bullet and numbered
        },
        {
          type: "image",
        },
        { type: "youtubeOrVimeo" },
      ],
    },
    {
      name: "excerpt",
      title: "Excerpt",
      type: "string",
    },
    {
      name: "coverImage",
      title: "Cover Image",
      type: "image",
      options: {
        hotspot: true,
      },
    },
    {
      name: "date",
      title: "Date",
      type: "datetime",
    },
    {
      name: "author",
      title: "Author",
      type: "reference",
      to: [{ type: "author" }],
    },
    {
      name: "tags",
      title: "Tags",
      type: "array",
      of: [
        {
          type: "reference",
          to: [{ type: "tag" }],
        },
      ],
    },
  ],
  preview: {
    select: {
      title: "title",
      author: "author.name",
      media: "coverImage",
    },
    prepare(selection) {
      const { author } = selection;
      return { ...selection, subtitle: author && `by ${author}` };
    },
  },
};