在Rails中手动创建表单字段，rails在编辑时如何自动填充字段？

Question

I am creating a form in Rails by hand, ie:

<input type="number" name="funds_application[product_revenues_attributes][1][amount]">

This works fine when submitting data, but when I am editing a record the fields do not auto populate. Does anyone know how rails does this? Do I need to use a <%= text_field_tag %> to get that part of it working.

This is a small part of a larger form where I am using Simple_form, and the rest works as expected. I find complex forms sort of mind melting in rails, what does it want?

Answer 1

Do you have to do it by hand? Can you still use form helpers ?

Anyways, the way Rails does it is that you always give the form an instance of the model you are working with, and call the getter on its attributes. For a new instance, they'll be blank. For a saved instance, they'll have values. For instance, if you had a User model with a login and name attribute, you could do @user = User.new in your controller, and in your form do (using helper tags):

<%= text_field_tag "login", @user.login %>
<%= text_field_tag "name", @user.name %>

And if you had an actual user ( @user = User.first ), you could still use it with that view.

So no, you don't have to use the form tags, because the underlying principle is always giving an instance of the model you are working with, and deciding what defaults to use if an attribute is nil/blank.

So if you always had an object to work with, and yet still wanted to do it manually, you could type:

<input type="number" name="funds_application[product_revenues_attributes][1][amount]" value=@my_object.amount>

Or whatever the field really is. That way, it gets some default value, but if the object already has something for that attribute, it will output it.

Answer 2

If you're building the form yourself, you can populate the fields yourself from the object passed in, with code along these lines:

<input type="number" name="funds_application[product_revenues_attributes][1][amount]" value="<%= @model.value %>">

The most railsy way to do it is with the form_for construct, though. The guide on this is pretty good.