vue-rails-form-builder

A custom Rails form builder for Vue.js

<%= vue_form_for User.new do |f| %>
  <%= f.text_field :name %>
<% end %>

<form ...>
  ...
  <input v-model="user.name" type="text" name="user[name]" ... />
</form>

Add the following line to Gemfile:

gem "vue-rails-form-builder"

Run bundle install on the terminal.

<%= vue_form_for User.new do |f| %>
  <%= f.text_field :name %>
  <%= f.submit "Create" %>
<% end %>

The above ERB template will be rendered into the following HTML fragment:

<form class="new_user" id="new_user" action="/users" accept-charset="UTF-8" method="post">
  <input name="utf8" type="hidden" value="&#x2713;" />
  <input type="hidden" name="authenticity_token" value="..." />
  <input v-model="user.name" type="text" name="user[name]" id="user_name" />
  <input type="submit" name="commit" value="Create" />
</form>

Note that the third <input> element has a v-model attriubte, which can be interpreted by Vue.js as the directive to create two-way data bindings between form fields and component's data.

If you are using the Webpacker, create app/javascript/packs/new_user_form.js with following code:

import Vue from 'vue/dist/vue.esm'

document.addEventListener("DOMContentLoaded", () => {
  const NewUserForm = new Vue({
    el: "#new_user",
    data: {
      user: {
        name: ""
      }
    }
  })
})

Add this line to the ERB template:

<%= javascript_pack_tag "new_user_form" %>

Then, you can get the value of user[name] field by the user.name.

If you use Rails 5.1 or above, you can also use vue_form_with:

<%= vue_form_with model: User.new do |f| %>
  <%= f.text_field :name %>
  <%= f.submit "Create" %>
<% end %>

Visit vue-rails-form-builder-demo for a working Rails demo application using the vue-rails-form-builder.

To vue_form_for and vue_form_with methods you can provide the same options as form_for and form_with.

There is a special option:

• :vue_scope - The prefix used to the input field names within the Vue component.

This gem provides two additional helper methods: vue_tag and vue_content_tag.

Basically, they behave like tag and content_tag helpers of Action Views. But, they interpret the HTML options in a different way as explained below.

If the HTML options have a :bind key and its value is a hash, they get transformed into the Vue.js v-bind directives.

In the example below, these two lines have the same result:

<%= vue_content_tag(:span, "Hello", bind: { style: "{ color: textColor }" }) %>
<%= vue_content_tag(:span, "Hello", "v-bind:style" => "{ color: textColor }" }) %>

Note that you should use the latter style if you want to specify modifiers to the v-bind directives. For example:

<%= vue_content_tag(:span, "Hello", "v-bind:text-content.prop" => "message" }) %>

If the HTML options have a :on key and its value is a hash, they get transformed into the Vue.js v-on directives.

In the example below, these two lines have the same result:

<%= vue_content_tag(:span, "Hello", on: { click: "doThis" }) %>
<%= vue_content_tag(:span, "Hello", "v-on:click" => "doThis" }) %>

Note that you should use the latter style if you want to specify modifiers to the v-on directives. For example:

<%= vue_content_tag(:span, "Hello", "v-on:click.once" => "doThis" }) %>
<%= vue_content_tag(:button, "Hello", "v-on:click.prevent" => "doThis" }) %>

If the HTML options have a string value (not a boolean value) for checked, disabled, multiple, readonly or selected key, the key gets transformed by adding v-bind: to its head.

In the example below, these two lines have the same result:

<%= vue_content_tag(:button, "Click me!", disabled: "!clickable") %>
<%= vue_content_tag(:button, "Click me!", "v-bind:disabled" => "!clickable") %>

If you want to add a normal attribute without v-bind: prefix, specify true (boolean) to these keys:

<%= vue_content_tag(:button, "Click me!", disabled: true) %>

This line produces the following HTML fragment:

<button disabled="disabled">Click me!</button>

If the HTML options have one or more of the following keys

text, html, show, if, else, else_if, for, model, pre, cloak, once

then, these keys get transformed by adding v- to their head.

In the example below, these two lines have the same result:

<%= vue_tag(:hr, if: "itemsPresent") %>
<%= vue_tag(:hr, "v-if" => "itemsPresent") %>

Note that the :else_if key is transformed into the v-else-if directive:

<%= vue_tag(:hr, else_if: "itemsPresent") %>
<%= vue_tag(:hr, "v-else-if" => "itemsPresent") %>

When you build HTML forms using vue_form_for, the form building helpers, such as text_field, check_box, etc., have these additional behavior.

Example:

<%= vue_form_for User.new do |f| %>
  <%= f.text_field :name, model: "userName" %>
  <label>
    <%= f.check_box :administrator, on: { click: "doThis" } %> Administrator
  </label>
  <%= f.submit "Create", disabled: "!submittable" %>
<% end %>

When you build HTML forms using vue_form_for, the form builder has the vue_prefix method that returns the prefix string to the Vue.js property names.

See the following code:

<%= vue_form_for User.new do |f| %>
  <%= f.text_field :name %>
  <%= f.submit "Create", disabled: "user.name === ''" %>
<% end %>

The vue_prefix method of the form builder (f) returns the string "user" so that you can rewrite the third line of the example above like this:

  <%= f.submit "Create", disabled: "#{f.vue_prefix}.name === ''" %>

This method is convenient especially when the form has nested attributes:

<%= vue_form_for @user do |f| %>
  <%= f.text_field :name %>
  <%= f.fields_for :emails do |g| %>
    <%= g.text_field :address,
      disabled: "user.emails_attributes[#{g.index}]._destroy" %>
    <%= g.check_box :_destroy if g.object.persisted? %>
  <% end %>
  <%= f.submit "Create", disabled: "#{f.vue_prefix}.name === ''" %>
<% end %>

Using the vue_prefix method, you can rewrite the fifth line more concisely:

      disabled: g.vue_prefix + "._destroy" %>

As the official Vue.js document says:

v-model will ignore the initial value, checked or selected attributes found on any form elements. (https://vuejs.org/v2/guide/forms.html)

Because of this, all form controls get reset after the Vue component is mounted.

However, you can use vue-data-scooper plugin in order to keep the original state of the form.

The vue-rails-form-builder is distributed under the MIT license. (MIT-LICENSE)

Tsutomu Kuroda (t-kuroda@oiax.jp)