Takehiro Adachi

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08 Jan 2013
Strong Parameters with accepts_nested_attributes_for

In Rails4, there will be a feature called “strong parameters” included in default.

The basic info about the strong parameters could be found here.

So basically you write something like below, and decide which column could be changed when you use mass assignment.

  # Using a private method to encapsulate the permissible parameters is just a good pattern
  # since you'll be able to reuse the same permit list between create and update. Also, you
  # can specialize this method with per-user checking of permissible attributes.
  def person_params
    params.required(:person).permit(:name, :age)

So the important part is the below line.

params.required(:person).permit(:name, :age)

First, you appoint which model you are going to use. Then you permit which column is accessible by using the permit function, by giving the symbol names of columns.

But what are we going to do when we use accepts_nested_attributes_for?( btw, if you don’t know what accepts_nested_attributes_for is, check this post )

When we use accepts_nested_attributes_for and assign nested models, basically the params goes like the below.


So we have the get rid of the keys of the nested model.

There’s a very good way to permit the nested models column.

params.require(:page).permit(:name, :desc, images_attributes: :image_name)

That’s it! :D

Btw the commit of this feature could be found in this Pull Request.

Takehiro Adachi at 17:33

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