How to include child associations when serializing to json? - ruby-on-rails

Question

Before using fast_jsonapi gem I was doing this:
render json: school.to_json(include: [classroom: [:students]])
My SchoolSerializer looks like:
class SchoolSerializer
include FastJsonapi::ObjectSerializer
attributes :name, :description, :classroom
end
How would I get the students included in the JSON result?
Also, the classroom association is including but it is displaying all the properties, is there a way to map the classroom property to a ClassroomSerializer ?
class School < ApplicationRecord
belongs_to :classroom
end
class Classroom < ApplicationRecord
has_many :students
end

Answer 1

class SchoolSerializer
include FastJsonapi::ObjectSerializer
attributes :name, :description
belongs_to :classroom
end
# /serializers/classroom_serializer.rb
class ClassroomSerializer
include FastJsonapi::ObjectSerializer
attributes :.... #attributes you want to show
end
Also you can add additional association to your School model, to access Students.
like this
has_many :students, through: :classroom
and then include it in School serializer directly.
Update: also please note that you can directly point to serializer class you need. (if you want to use class with different name from model as example).
class SchoolSerializer
include FastJsonapi::ObjectSerializer
attributes :name, :description
belongs_to :classroom, serializer: ClassroomSerializer
end

Answer 2

render json: SchoolSerializer.new(school, include: "classrooms.students")
The difference being the use of "include" when rendering the serializer. This tells the Serializer to add a key "included" to the returned JSON object.
class SchoolSerializer
include FastJsonapi::ObjectSerializer
belongs_to :classroom
has_many :students, through: :classroom
attributes :school_name, :description
end
StudentSerializer
include FastJsonapi::ObjectSerializer
belongs_to :classroom
belongs_to :school
attributes :student_name
end
render json: SchoolSerializer.new(school).serialized_json
will return a series of students with only the top level identifiers in the form
data: {
id: "123"
type: "school"
attributes: {
school_name: "Best school for Girls",
description: "Great school!"
...
},
relationships: {
students: [
{
id: "1234",
type: "student"
},
{
id: "5678",
type: "student"
}
]
}
}
whereas the include: "classroom.students" will return the full serialized Student Records in the form:
data: {
id: "123"
type: "school"
attributes: {
school_name: "Best school for Girls"
...
},
relationships: {
classroom: {
data: {
id: "456",
type: "classroom"
}
},
students: [
{
data: {
id: "1234",
type: "student"
}
},
{
data: {
id: "5678",
type: "student"
}
}
]
},
included: {
students: {
data {
id: "1234",
type: "student",
attributes: {
student_name: "Ralph Wiggum",
...
},
relationships: {
school: {
id: "123",
type: "school"
},
classroom: {
id: "456",
type: "classroom"
}
}
},
data: {
id: "5678",
type: "student",
attributes: {
student_name: "Lisa Simpson",
...
},
relationships: {
school: {
id: "123",
type: "school"
},
classroom: {
id: "456",
type: "classroom"
}
}
}
},
classroom: {
// Effectively
// ClassroomSerializer.new(school.classroom).serialized_json
},
}
}