如何查询Knex.js的多对多关系？

Question

我在 Postgres 中有这样的多对多关系：

// migrations/2020_create_initial_tables.js

exports.up = function(knex) {
  return knex.schema
    .createTable('students', function(table) {
      table.increments('id').primary()
      table
        .string('email')
        .unique()
        .index()
      table.string('password')
    })
    .createTable('courses', function(table) {
      table.increments('id').primary()
      table.string('title').notNullable()
      table.text('description')
    })
    // A student can enroll many courses
    // A course can have many students
    .createTable('student_courses', function(table) {
      table.increments('id').primary()
      table
        .integer('student_id')
        .references('id')
        .inTable('students')
      table
        .integer('course_id')
        .references('id')
        .inTable('courses')
    })
    .catch(err => {
      console.error(err)
      throw err
    })
  // .finally(() => knex.destroy());
}

exports.down = function(knex) {
  return knex.schema
    .dropTableIfExists('students')
    .dropTableIfExists('courses')
    .dropTableIfExists('student_courses')
    .catch(err => {
      console.error(err)
      throw err
    })
}

我需要显示学生已注册的课程。如何通过 student.id 查询 courses 的（all/an 数组）？

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堆栈：打字稿，knex@v0.20.12，Postgres@12-alpine，pg@v7.18.2

Answer 1

const coursesOfSingleStudent = await knex('courses').whereIn('id',
   knex('student_courses').select('course_id').where('student_id', studentId)
)

尽管使用 objection.js 可能会更好，它允许您声明关系映射然后直接查询：

const studentWithCourses = await Student.query().findById(studentId).withGraphFetched('courses');

如何查询Knex.js的多对多关系？

How to query many to many relations with Knex.js?

javascript

sql

node.js

postgresql

knex.js