通过定制选择导轨订购

Question

I am in the process of moving our admin system over from PHP to Ruby On Rails. There was a part of the old system that used SQL to build a list of customers and then order them by the time at which they was last contacted:

    SELECT 
      `customer`.*, (
        SELECT MAX(`date`)
        FROM `customer_contact`
        WHERE `customer`.`Customer_ID`=`customer_contact`.`customer_id`
        ORDER BY `date` DESC
        LIMIT 1
      ) AS `last_contacted`
    FROM
      `lead_details`
    GROUP BY `customer`.`Company_Name`
    ORDER BY `last_contacted`
    LIMIT 50

The customer table is now in the Customer model and the customer_contact is now in a CustomerCallback model. I want to build a similar list using rails and preferably without using that raw SQL. There's about 10,000 customer records so the way I've figured to do it at the moment (pull all customers, check their last contact and then order an array by that) would be incredibly inefficient.

Any pointers?

So it orders a list of customers by the highest date of its children and then limits that to stop pulling in 10,000 records like the SQL above.

I apoligise if this is tough to understand, but it's hard to put into words

Answer 1

Since that's so customized, I would suggest using select_rows , like:

customers = Customer.connection.select_rows("SELECT 
    `customer`.*, (
      SELECT MAX(`date`)
      FROM `customer_contact`
      WHERE `customer`.`Customer_ID`=`customer_contact`.`customer_id`
      ORDER BY `date` DESC
      LIMIT 1
    ) AS `last_contacted`
  FROM
    `lead_details`
  GROUP BY `customer`.`Company_Name`
  ORDER BY `last_contacted`
  LIMIT 50")