向基础模型添加关系/关联模型值

Question

I have two objects, A and B . Each have many of the other, using relationshipA . relationshipA has a property propertyA . Can I merge the properties of relationshipA and either A or B when I perform a fetch?

For example

A.find(params[:id]).relationshipAs

I'd like that to return me Bs , but also append the properties from relationshipA into them, at least when rendering the json.

class A < ActiveRecord::Base

  has_many :relationship_a
  has_many :b, through: :relationship_a

end

class B < ActiveRecord::Base

  has_many :relationship_a
  has_many :a, through: :relationship_a

end

class RelationshipA < ActiveRecord::Base

    belongs_to :A
    belongs_to :B

end

Assuming B has properties prop1 , prop2 and prop3 and RelationshipA has prop4 , I'd like to get a json response from:

render json: A.find(params[:id]).bs

I'd like to expect:

[{
    'prop1' : 'value',
    'prop2' : 'value',
    'prop3' : 'value',
    'prop4' : 'value'
}, ...]

Here's a console example:

a1 = A.create
b1 = B.create
b2 = B.create
a1.bs = [b1, b2]
RelationshipA.where(a_id: a1.id).first.prop4 = 'Hello'
RelationshipA.where(a_id: a1.id).last.prop4 = 'There'
*now output all of a1's bs including the relationships' prop4 value*
#<ActiveRecord::Associations::CollectionProxy [#<B id: 1, prop1: nil, prop2: nil, prop3: nil, created_at: "2014-07-09 20:37:12", updated_at: "2014-07-09 20:37:12", prop4: 'Hello'>, #<B id: 2, prop1: nil, prop2: nil, prop3: nil, created_at: "2014-07-09 20:37:12", updated_at: "2014-07-09 20:37:12", prop4: 'There'>]>

Answer 1

I see 2 questions:

1. How do I generate custom json
2. How do I bring back objects to generate the custom json?

Defining a custom json method:

class A < ActiveRecord::Base
  has_many :relationships, :inverse_of :a
  has_many :bs, :through => :relationships
end

class B < ActiveRecord::Base
  # prop1
  has_many :relationships, :inverse_of :b
  has_many :as, :through => :relationships
end

class Relationship < ActiveRecord::Base
  # prop4
  belongs_to :a, inverse_of: :relationships
  belongs_to :b, inverse_of: :relationships
  def as_json(options: {})
    {
      prop1: b.prop1,
      prop4: prop4
    }
  end
end

relationships = A.includes(relationships: :b).find(params[:id]).relationships
puts relationships.to_json

The question is very abstract. If you can stick with Relationship objects, then that is probably your best bet. Using includes will give you a single or 2 queries.

If you need to have a B with the knowledge of how you brought back B , then you probably want to add attr_accessor :prop4 to B and an "extension" block to Relationship 's has_many clause to set B's :prop4 .

Answer 2

It seems the best that I can do is a hash of the values, but not through the initial query or any built in functions. @kbrock has a solid answer, but I prefer the attributes approach.

class A < ActiveRecord::Base
  has_many :relationships, :inverse_of :a
  has_many :bs, :through => :relationships

  # returns array of hashes, not json string, of all Relationship's and B's attributes
  def relationshipValues
    # get all of a's relationships, including `b`s with only 2 queries
    relationships = Relationship.includes(:b).where(a_id: :id).all
    relationshipValues = []
    # I'm not sure if this is optimal, so please offer some advice
    @relationships.each do |relationship|
        relationshipValues << relationship.attributes.merge(relationship.b.attributes)
    end
    # simple return - is there better way?
    relationshipValues
  #just for spacing :)
  end

end

class B < ActiveRecord::Base
  has_many :relationships, :inverse_of :b
  has_many :as, :through => :relationships
end

class Relationship < ActiveRecord::Base
  belongs_to :a, inverse_of: :relationships
  belongs_to :b, inverse_of: :relationships

  def to_json
    attributes.merge(b.attributes)
  end
end