[gatsby-plugin-feed] Document slug fields creation

[jiahaog]

I noticed that without configuration to create the slug fields, it will result in the following error:

error Plugin gatsby-plugin-feed returned an error


  Error: GraphQLError: Cannot query field "fields" on type "  MarkdownRemark".

  - internals.js:29
    [jiahaog.com]/[gatsby-plugin-feed]/internals.js:29:13

  - es6-promise.js:409 tryCatch
    [jiahaog.com]/[es6-promise]/dist/es6-promise.js:409:12

  - es6-promise.js:424 invokeCallback
    [jiahaog.com]/[es6-promise]/dist/es6-promise.js:424:13

  - es6-promise.js:176
    [jiahaog.com]/[es6-promise]/dist/es6-promise.js:176:14

  - es6-promise.js:128 flush
    [jiahaog.com]/[es6-promise]/dist/es6-promise.js:128:5

  - next_tick.js:131 _combinedTickCallback
    internal/process/next_tick.js:131:7

  - next_tick.js:180 process._tickCallback
    internal/process/next_tick.js:180:9

This has already been implemented in gatsbyjs/gatsby-starter-blog#70 but it's not immediately obvious when starting afresh on a new project, so I just copied the implementation over to the docs.

Cheers!

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[CrowsVeldt]

I just wanted to throw in my two cents, please let me know if this is out of place. I ran into this exact problem today, trying to add an RSS feed to my site. I'm still fairly new at this, and I found looking for the solution to be frustrating. Especially as the docs say that it should just work. A few months ago I probably would have just lost motivation and given up.

I did find the solution, and considered making a pull request myself to update the docs, but then I found this one. I hope this can get merged in quickly to hopefully prevent discouraging other beginners like myself.

[jiahaog]

@KyleAMathews is this okay to be merged? 😄

[jiahaog]

Or perhaps the accompanying logic should be moved into the gatsby-plugin-feed directly, I can try to change that

[KyleAMathews]

Oh sorry, forgot to reply to this. I hestitated to do anything here because @mikefowler has a WIP PR that fixes this another, better way #3413

Could you look through that PR/discussion and try helping it along?

gatsby-plugin-feed shouldn't require that slug exists so we should solve that directly instead of documenting it. Slug isn't a universal way of storing the page path.

[jiahaog]

Ah okay, I'll check it out then 👍