Sailsjs, using relationship, how to get the value of unrelated models?

Question

I have 3 models called "User, Pet and UserPet".

User model

"user_name" : {
    type: "string",
    required: true
},
"pets" : { 
   collection: 'pet',
   via: 'user',
   through: 'userpet'
}

Pet model

"pet_name" : { 
    type: "string",
    required: true   
}

UserPet Model

user: {
    model: 'user'
},

pet: {
    model: 'pet'
},

user_expected_price: {
  type: "float",
  required: true
}

Query used to retrieve data

User.find().populateAll().exec(function (err, data) { 
   console.log(data);
})

I can get all the data from the above models, except user_expected_price, in the userpet model, because this field is not associated with any model. I need this field value along with another answer. Does any body help me? The Sails document does not help me.