Full Error Message

The code was working fine locally, but I encountered an error when building in the production environment.

error "gatsby-plugin-mdx" threw an error while running the onCreateNode lifecycle:
duplicated mapping key at line 7, column -15:
    product_number:

I checked the error log carefully, but there was no specific file name indicating the cause of the error.

Solution

In this case, the error occurred because there was an .mdx file containing duplicate product_number fields.

By using VS Code's string search to look for product_number, I found the .mdx file that had two occurrences of the same key. After removing the duplicate, everything worked fine.

Files that might cause this error include:

• .yml
• .yaml
• .md
• .mdx
• .json

Additionally, in gatsby-node.js, you can log the file paths during the onCreateNode process:

exports.onCreateNode = ({ node }) => {
  if (node.internal.type === "MarkdownRemark" || node.internal.type === "Mdx") {
    console.log("Processing:", node.fileAbsolutePath)
  }
}

If I had logged the file paths when creating nodes, I could have resolved the issue without searching manually.

Hope this helps!