markdown Rails中的分页

Posted 2021-05-06

### Pagination
* Useful when your model contains many items that you would like to organize by displaying a 
few items at a time
* Accomplished by using the ruby gem, kaminari

```ruby
#add gem to gemfile
gem 'kaminari'
```

* Run `bundle`
* Kaminari provides a `page` scope that can be used on any ActiveReccord model (use the 
params `params[:page]` for this scope)

```ruby
#usage 
class ProductsController < ApplicationController
  def index
    @products = Product.order("name").page(params[:page])
  end
end
```

* In the index view page where you are listing the items of the model:

```ruby
# before any relevant code
<%= paginate @products %>

# other relevant code ...
```

* The **default** item count per page is **25**!
* This can be adjusted using another scope method that can be chained on to `page`,
called `per`. You can pass in the number of items per page as it's arguments.
* Must call `page` first on the ActiveRecord model.

```ruby
#usage 
class ProductsController < ApplicationController
  def index
    @products = Product.order("name").page(params[:page]).per(5)
  end
end
```

* For more customizations (changing the word "prev" to something else)
    * locate the`en.yml` file in `config/locales/en.yml`

```ruby
# should contain the following
en:
  hello: "Hello world"

# you can add the following:
  views:
    pagination:
      previous: "&lt; Previous"
      next: "Next &gt;"
      truncate: "..." # default style is 3 dots
      
```

#### Using Kaminari on non ActiveRecord array:

```ruby
# if the array you are using is not an ActiveRecord array, but a generic ruby array
# you can still paginate the array by ading on the following:
@array = Kaminari.paginate_array(generic_array).page(params[:page]).per(4)
```

### Incorporate AJAX inside Pagination
* Set the Kaminari gem (follow instructions above)
* For the main action (for example index) that contains the table (or thing to be paginated), make sure it `responds_to` a format block with options for html and js
* Make sure there are views index.html and index.js!
* In the action that does an ajax call that manipulates the DOM, (ex. `table_sort`), make sure that it `respond_to :js`!

```ruby
# in your .js.erb file:
$("#team-quote-table-body").html("<%= j render partial: 'team_quotes', locals: {team_quotes: @team_quotes} %>");

$('#paginator').html("<%= escape_javascript(paginate(@team_quotes, :remote => true).to_s) %>");
```

* IMPORTANT: Make sure to wrap `<%= paginate @model %>` is WRAPPED in a div with an id of paginator!

```ruby
<div id="paginator">
	<% if @team_quotes && @team_quotes.length > 0 %>
		<%= paginate @team_quotes, :remote => true %>
	<% end %>
</div>
```

* If you error `undefined method current_page for #`: this means the `page` method is not being called on the collection being returned, recheck to see if your
later sql calls alter the results:

```ruby
@team_quotes = Fsi::Quote.where(quote_manager_id: @quote_manager.id).page(params[:page]).per(2)    #calling it here is safe

# Click on the icon, check for header and sort
if !params["header"].blank? && !params["sort"].blank?
	# check for the search param
	if !params["search_term"].blank? 
		search = !params["search_term"].blank? ? params["search_term"] : ""
		@team_quotes = @team_quotes.quick_search(search)

	end

	db_fields = {
		"Created" => "created_at",
		"Sales Rep" => "sales_rep"
	}

	header = db_fields[params["header"]]
	sort = params["sort"].upcase if params["sort"]
	@team_quotes = @team_quotes.order_by_created(sort) if header == "created_at"
	@team_quotes = @team_quotes.order_by_sales_rep(sort) if header == "sales_rep"
else
	# ONLY SEARCH
	if !params["search_term"].blank? 
		search = !params["search_term"].blank? ? params["search_term"] : ""
		@team_quotes = @team_quotes.quick_search(search)
	end

end
```