Get average from nested eloquent relationship - mysql

Question

I would like to calculate average from nested relationship between eloquent models. So, let's say, I have 3 tables called programs, activities and statistics.
For simplicity sake, I will try to minimize the structure as follows:
program table:
-------------
| id | name |
-------------
| 1 | Foo |
| 2 | Bar |
-------------
activities table:
-----------------------------------
| id | program_id | name |
-----------------------------------
| 1 | 1 | Foo 1 |
| 2 | 1 | Foo 2 |
| 3 | 1 | Foo 3 |
| 4 | 2 | Bar 1 |
| 5 | 2 | Bar 2 |
-----------------------------------
statistics table:
-----------------------------------
| id | activity_id | type | score |
-----------------------------------
| 1 | 1 | A | 25 |
| 2 | 1 | B | 20 |
| 3 | 1 | A | 22 |
| 4 | 2 | A | 27 |
| 5 | 2 | B | 24 |
| 6 | 3 | A | 23 |
-----------------------------------
Now, what I want to get is the average of score of a program with specific type of statistic. I defined relationship in models, and tried following code, but no avail:
$program = Program::find(1);
$avg = $program->activities->where('statistics.type', 'A')->avg('statistics.value');
$avg always 0 or null if there is no activities in program, even without where clause.
i'm sure that i defined the relationship correctly because $program->activities returns a sets of activities and $activity-> statistics return a sets of statistics as well.
Any ideas?

Answer 1

You can use whereHas() like this:
Statistics::whereHas('activity', function ($q) use($programId) {
$q->where('program_id', $programId);
})
->where('type', 'A')
->avg('score');
Make sure you've defined activity relationship which should be "statistics belongsTo() activity".