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Jonathan Reinink: Dynamic relationships in Laravel using subqueries

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[开发(php) 所属分类 开发(php) | 发布者 店小二04 | 时间 2018 | 作者 红领巾 ] 0人收藏点击收藏

In a recent post to his site Jonathan Reinink has written up a guide to using dynamic (Eloquent) relationships in Laravel applications by making use of subquery functionality. In it, he shows how to make use of the selectSub method to select additional information in a single query versus having the overhead of custom, hard-coded relationships.

Developers are typically pretty good at the first goal. We're aware of N+1 style problems, and use techniques like eager-loading to limit database queries. However, we're not always the best at the second goalkeeping memory usage down. In fact, we sometimes do more harm than good trying to reduce database queries at the expense of memory usage.

He starts off with the challenge he's trying to solve: gathering login information for users in a performant way. He includes the schema for the users and logins table and shows the code of how a normal relationship select might look to get login information for each user (creating an N+1 issue ).

To help solve the issue, they try caching the last login information but realize they can do better - this is where subqueries come in. They provide an example of using the selectSub method to get the login information, mapping it to a macro for easier use and defining scopes. Finally, the tutorial shows how to use this method to select information via dynamic relationships. It also talks about lazy-loading issues and if the same thing could be accomplished with a "has one" relationship.

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