N 1 query problem refers to the execution of additional query on each piece of data after obtaining a set of data, resulting in a large number of repeated requests. For example, after taking out 100 article records, each article will query the author information separately, and a total of 101 queries will be performed. Discovery methods include using the Laravel Debugbar plug-in, enabling query logs to observe duplicate SQL, and using IDE or static analysis tools to detect unpreloaded relationships. The solution is to use Eager Loading preloading, such as Post::with('author')->get(), which can load the associated data at one time to reduce the number of queries; supports multi-layer nesting with('author.socialMedia'); or load('author') dynamically. Other tips include constraining preload fields, delaying preloading, avoiding overloading, and paying attention to memory usage during big data paging.
You may encounter performance bottlenecks when developing Laravel applications, and one of the most common reasons is the N 1 query problem . It refers to the execution of an additional database query on each piece of data after a set of data is obtained, resulting in a large number of repeated requests.

What is an N 1 query?
Simply put, it is to execute a database query in a loop. For example, you take out 100 article records from the database and then query the author information for each article separately:
$posts = Post::all(); foreach ($posts as $post) { echo $post->author->name; }
This code will first execute a query to obtain all articles (1 time), and then execute a query to obtain the author (100 times), which is a total of 101 queries - this is the origin of "N 1".

How to find N 1 query?
In actual development, N 1 queries are not always so obvious. You can find it in the following ways:
- Use the Laravel Debugbar plugin to view how many SQL queries are executed during the page loading process.
- Turn on the query log in the log to observe whether there are a large number of duplicate SQL statements.
- Use the IDE or static analysis tool to detect if the model relationship call is not preloaded.
If you see a query for an associated model being executed repeatedly, you may encounter N 1 problems.

How to solve it? Preload using Eager Loading
Laravel provides a very convenient function called preloading , which can load associated data at one time and avoid multiple queries in a loop.
Basic usage:
$posts = Post::with('author')->get();
In this way, Laravel will retrieve all relevant authors at once while obtaining the article, and only perform two queries (1 article and 1 author).
Multi-layer nesting:
If the author is also associated with data, such as socialMedia, you can also write it like this:
$posts = Post::with('author.socialMedia')->get();
Dynamic loading:
Sometimes you want to load the associated data later, you can use load()
method:
$posts = Post::all(); $posts->load('author');
Other tips and precautions
In addition to the basic with()
, you can also combine some other methods to optimize:
Constraint preload : only load the required data
Post::with(['author' => function($query) { $query->select('id', 'name'); }])->get();
Delayed preloading : suitable for cases where certain conditions are judged and loaded again
$post = Post::find(1); if ($someCondition) { $post->load('comments'); }
Avoid over-preloading : Don't blindly bring all relationships with you, only loading the fields and models you really need.
Be careful when processing big data by paging : Although preloading is efficient, if the data is large, it may also cause excessive memory usage.
Let's summarize
N 1 query problems are common, but they are also easy to solve. As long as you remember to use with()
when accessing model relationships, it can greatly reduce the number of database requests and improve application performance.
Basically that's it. Just be careful not to trigger model association query in the loop.
The above is the detailed content of What is the N 1 query problem and how to solve it in Laravel?. For more information, please follow other related articles on the PHP Chinese website!

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