原生SQL查询转Eloquent关联后续问题：模型预加载咨询

嘿，我注意到你已经给County和Freguesia模型搭好了关联关系，现在想把指定的原生SQL查询转换成对应的Eloquent关联写法对吧？不过你还没贴出具体要转换的原生SQL语句呢😉。先结合你现有的模型代码，我给你举几个常见场景的转换示例，帮你快速上手：

• County模型：通过freguesias()方法和Freguesia建立了一对多关联（一个County对应多个Freguesia）
• Freguesia模型：
  • 通过county()方法和County建立了反向从属关联（每个Freguesia属于一个County）
  • 通过weathers()方法和Weather建立了一对多关联（一个Freguesia对应多条Weather数据）

示例1：关联查询County及其下属Freguesia #

假设你的原生SQL是这样的：

SELECT counties.*, freguesias.id AS freg_id, freguesias.name AS freg_name
FROM counties
LEFT JOIN freguesias ON counties.id = freguesias.id_county
WHERE counties.id = 5

对应的Eloquent写法可以用预加载（with）来实现：

// 简单预加载所有关联字段
$county = County::with('freguesias')->find(5);

// 或者只加载需要的字段，提升性能
$county = County::with(['freguesias' => function($query) {
    $query->select('id', 'id_county', 'name');
}])->find(5);

示例2：多层关联查询（County → Freguesia → Weather） #

如果你的原生SQL涉及三层关联查询：

SELECT counties.name AS county_name, freguesias.name AS freg_name, weathers.temperature, weathers.recorded_at
FROM counties
JOIN freguesias ON counties.id = freguesias.id_county
JOIN weathers ON freguesias.id = weathers.id_freg
WHERE counties.id = 5 AND weathers.recorded_at >= '2024-01-01'

对应的Eloquent可以用嵌套预加载，还能在闭包里添加筛选条件：

$county = County::with(['freguesias' => function($fregQuery) {
    $fregQuery->select('id', 'id_county', 'name')
              ->with(['weathers' => function($weatherQuery) {
                  $weatherQuery->select('id', 'id_freg', 'temperature', 'recorded_at')
                               ->where('recorded_at', '>=', '2024-01-01');
              }]);
}])->find(5);

你把需要转换的具体原生SQL贴出来，我就能帮你精准转换成适配你模型关联的Eloquent写法啦！

内容的提问来源于stack exchange，提问作者Hula Hula