在ActiveRecord对象中查找(Find in ActiveRecord object)

在ActiveRecord对象中查找(Find in ActiveRecord object)

我有一个页面，我可以显示所有客户的详细信息，或者如果在参数中指定，只显示一个客户的详细信息。

我的控制器看起来像这样。

def display_customers @all_customers = Customer.all if params[:customer_id] @customers = Customer.find(:all, conditions: ["id = ?", params[:customer_id]]) else @customers = @all_customers end end

我使用@all_customers来填充客户的下拉列表。 我使用@customers来完成每个客户的each循环。 然后，如果指定了customer_id参数，则@customers将只是单个客户。

这很好用，但@customers = Customer.find(...)是一个额外的数据库查询。 我已经拥有@all_customers所有客户，所以我可以更好地从那里获取我需要的一条记录 - 而不是再次回到数据库。

I have a page where I can either display all customers' details, or if specified in the params, just one customer's details.

My controller looks something like this.

def display_customers @all_customers = Customer.all if params[:customer_id] @customers = Customer.find(:all, conditions: ["id = ?", params[:customer_id]]) else @customers = @all_customers end end

I use @all_customers to populate a dropdown of customers. I use @customers to perform an each loop through each customer. Then, if the customer_id param is specified, @customers will just be the single customer.

This works just fine but @customers = Customer.find(...) is an extra DB query. I already have all the customers in @all_customers so I though there would be a better way to grab the one record I need from there - instead of going back to the DB again.

最满意答案

你可以使用所有Enumerables内置的find ...

if params[:customer_id] @customer = @all_customers.find { |c| c.id == params[:customer_id] } else #...

......但可能不应该。

根据记录的数量，这可能不会更快，因为您的数据库查询将使用索引，其中上述代码使用线性搜索所有返回的记录。 机会是第二个数据库查询是要走的路。

您还应该重写您的查询。 Rails足够聪明，你不必在通过ID查找记录时传递条件; 你找到它。 这些是相同的：

# BAD: @customers = Customer.find(:all, conditions: ["id = ?", params[:customer_id]]) # BETTER: @customers = Customer.find_by_id(params[:customer_id]) # BEST: @customer = Customer.find(params[:customer_id])

如果你真的想要它是一个数组，只需将结果包装在[] 。

You can use the find which is built in to all Enumerables...

if params[:customer_id] @customer = @all_customers.find { |c| c.id == params[:customer_id] } else #...

... but probably shouldn't.

Depending on the number of records, this may not be any faster, as your database query will use an index, where the above code uses a linear search through all the returned records. Chances are a second database query is the way to go.

You should also rewrite your query. Rails is smart enough that you don't have to pass conditions when finding a record by its ID; you just find it. These are identical:

# BAD: @customers = Customer.find(:all, conditions: ["id = ?", params[:customer_id]]) # BETTER: @customers = Customer.find_by_id(params[:customer_id]) # BEST: @customer = Customer.find(params[:customer_id])

If you really want it to be an array, just wrap the result in [].