Not if you set up your foreign key constraints and it looks like you have. You can use belongs_to in your schema (Not required but it’s explicit 
) and in your changeset you can use foreign_key_constraint
schema "user_resources" do
belongs_to :resource, Resource
belongs_to :user, User
field :inserted_by, :integer
field :updated_by, :integer
timestamps()
end
def changeset(user_resource, attrs) do
user_resource
|> cast(attrs, [:user_id, :resource_id, :inserted_by, :updated_by])
|> validate_required([:user_id, :resource_id, :inserted_by, :updated_by])
|> foreign_key_constraint(:user_id)
|> foreign_key_constraint(:resource_id)
end
If the resource or user do not exist this will give you an error changeset.
