我在数据库中创建了两个表，products 和 shopping_list。我已经为产品提供了一个外键参考 shopping_list，即 product.shopping_list_id。
我正在尝试在 ruby on rails 中查找购物清单中存在的全部产品，但出现错误。
我给了一个文本框来输入值，该值作为总项目存储在数据库中。
但是当我在数据库中添加新产品时，数据库中的数量没有更新。
我的 shopping_list 表如下：-
CREATE TABLE shopping_lists
(
id serial NOT NULL,
shopping_list_name character varying(255),
shopping_list_status character varying(255) DEFAULT 'OPEN'::character varying,
total_items character varying(255) DEFAULT 0,
created_at timestamp without time zone NOT NULL,
updated_at timestamp without time zone NOT NULL,
deleted integer NOT NULL DEFAULT 0,
CONSTRAINT shopping_lists_pkey PRIMARY KEY (id)
)
我的产品表如下：-
CREATE TABLE products
(
id serial NOT NULL,
shopping_list_id integer NOT NULL,
product_name character varying(255) DEFAULT 'null'::character varying,
product_category character varying(255),
quantity integer,
status character varying(255) DEFAULT 'OPEN'::character varying,
deleted integer NOT NULL DEFAULT 0,
CONSTRAINT products_pkey PRIMARY KEY (id)
)
我的 Html 文档，即我在其中输入值的列表是这样的：-
<head>
<%= javascript_include_tag :application %>
<%= csrf_meta_tag %>
</head>
<% if @shopping_lists.blank? %>
<p>There are no shopping_lists currently in the system.</p>
<% else %>
<p>These are the shopping_lists in the system</p>
<table border="1">
<tr><td>shopping_list No.</td><td>shopping_list Name</td><td>status</td><td>quantity</td><td>Edit</td><td>Delete</td></tr>
<% @shopping_lists.each do |c| %>
<tr>
<td><%= link_to c.id, {:action => 'get_product', :id => c.id} %> </td>
<td><%= c.shopping_list_name %> </td>
<td><%= c.shopping_list_status %> </td>
<td><%= c.total_items %> </td>
<td><%= link_to 'Edit', {:action => 'edit', :id => c.id} %> </td>
<td><%= link_to 'Delete', {:action => 'delete', :id => c.id},
:data => { :confirm => "Are you sure you want to delete this shopping_list?" } %></td>
</tr>
<% end %>
</table>
<% end %>
<p><%= link_to "Add new shopping_list", {:action => 'new' }%></p>
简而言之，我想实现以下查询：-
Select count(*) from products where shopping_list_id = '';
你能帮我么