rebuild assoc if validation failed

i have Post and Image model. Post has many images. Also have nested form with dinamic images. If validation fails it return changeset without assoc loaded. How i can return user entered data to post and display errors to user?

#Ecto.Changeset<action: :insert,
 changes: %{category: "APET",
   images: [#Ecto.Changeset<action: :insert,
     changes: %{uuid: "a2cf8c14-3cc6-11e8-b152-c85b76d3a09f"},
     errors: [url: {"is invalid",
       [type: Olist.Images.Uploader.Type, validation: :cast]}],
     data: #Olist.Images.Image<>, valid?: false>], user_id: 1},
 errors: [heading: {"can't be blank", [validation: :required]},
  body: {"can't be blank", [validation: :required]},
  price: {"can't be blank", [validation: :required]},
  zipcode: {"can't be blank", [validation: :required]}],
 data: #Olist.Postings.Posting<>, valid?: false>
%Olist.Postings.Posting{__meta__: #Ecto.Schema.Metadata<:built, "postings">,
 address_1: nil, address_2: nil, body: nil, category: nil, heading: nil,
 id: nil,
 images: #Ecto.Association.NotLoaded<association :images is not loaded>,
 inserted_at: nil, price: nil, remote_id: nil, send: nil, updated_at: nil,
 user_id: nil, zipcode: nil}

on my form i try this

<div class="row">
    <div class="col-sm-12" id="image-list">
      <%= for image <- do
        render "image_fields.html", f: f
      end %>

Is it really the case? Do the validations fail and return without assocs or does Repo.insert do that?

I suspect the latter. Although it would help if I could see some more of your code where you call changeset, where you define your validations, and where you call Repo.insert or Repo.update.