How to use laravel hasManyThrough to parse?

The following tutorial column from Laravel will introduce you to the usage and parameters of laravel hasManyThrough. I hope it will be helpful to you!

The first case, I call it conductive association table (simple mode)

There are many users in the country, and the users have many posts

countries
    id - integer
    name - string

users
    id - integer
    country_id - integer
    name - string

posts
    id - integer
    user_id - integer
    title - string

How to query all posts in a certain country?

countries is this table, posts is the target table to be output, and users is the intermediate table

return $this->hasManyThrough('App\Post', 'App\User', 'country_id', 'user_id');

The second case is the intermediate table (pure intermediate table)

exam_paper(试卷表)id
nameexam_paper_question(试卷与试题中间表)id
exam_paper_id
question_idexam_question(试题表)id
name

We want to query the question through the id of exam_paper

return $this->hasManyThrough('exam_question', 'exam_paper_question', 'exam_paper_id', 'id'，'id'，'question_id');

// 参数1 目标表类名
exam_question,
// 参数2 枢纽表类名
exam_paper_question,
// 参数3 枢纽表中和当前表关联的字段名
'exam_paper_question.exam_paper_id',
// 参数4 目标表和枢纽表关联的字段名
'exam_question.id',
// 参数5 当前表中和枢纽表关联的字段名
'exam_paper.id',
// 参数6 枢纽表和目标表关联的字段名
'exam_paper_question.question_id');

If the current table is marked as A, the target table is marked as B, the intermediate table is marked as C, and the 6 parameters are marked as (B, C, CA, BC, AC, CB)

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