collection_select with form_for/form_with

collection_select is a ruby on rails form helper method that is used in place writing a form out in html. On the user side it looks like a drop down menu where the user makes a selection. Through my searches I couldn’t quite find a plain explanation for collection_select and what arguments you need to give to it, so here I will attempt to explain it as simply as I can.

In the picture below is a basic form to create a new song that has the attributes: name, artist, and genre. When a user creates a new song I want them to be able to select from pre existing artists and genres. I already have @artists and @genres set equal to Artist.all and Genre.all in my SongsController.

OK so what are the arguments you need for a collection_select method? They go in this order:

  1. The first argument you need to give the collection_select is what you want the key to be inside of your params hash and in my example I am wanting the artist id to be the key(:artist_id). You want to name this what the column is called inside of your database.
  2. The second argument you need to give it is an array of objects to iterate through(@artists or Artist.all could have worked as well).
  3. The third argument you need is what you want to get from that object so in my case it was the id of the artist(:id)
  4. The last argument you need is what you want the user to see when they are looking through the drop down menu. I wanted the user to be able to see the name of the artist(:name)


When not using collection_select within a form helper method there is an argument that must come before the ones I listed above and that is an object argument. Since I was working inside of a form that didn’t need to be included because rails already knew my object was a song.

Also when you are getting the data from the form it will be a nested hash so you will need to employ either a strong_params method or require then permit the data that you want to use.

Here is a link to more on strong_params: