如何在两个相关模型中使用PHP Laravel Eloquent groupBy和sum方法？

Question

I have three models Country , Province and District . Country has a one-to-many relationship with both Province and District models. And Province has a one-to-many relationship with District model. The District model has province_id as a foreign key.

In the District model I have a population to sum. I want to get the sum of a population for each province.

$population = Country::where(['name' => $c_name])->first()->districts;
$num = $population->groupBy('province_id')->map(function ($row) {
    return $row->sum('population_m');
});

SQL Query:

SELECT provinces.name, SUM(districts.population_m) AS population_m, SUM(districts.population_f) AS population_f FROM provinces
LEFT JOIN districts ON provinces.id = districts.province_id
GROUP BY provinces.name;

The above returns the province id but I want the province name with it.

Answer 1

You are telling it to group by province_id: $population->groupBy('province_id') . Instead, you can pass a function to the groupBy() collection method to tell it how to group the items inside:

https://laravel.com/docs/5.7/collections#method-groupby

Try something like this:

$population = Country::where(['name' => $c_name])->first()->districts;
$num = $population->groupBy(function($district, $key) {
    return $district->province->name;
})->map(function ($row) {
    return $row->sum('population_m');
});

Answer 2

尝试这个：

$population = Country::where(['name' => $c_name])->first()->districts()->with('province')->get();