Custom functions in MyProject.Repo

[Steve Pallen]

I'm trying to get custom functions working in my Repo. 

I have done the following:

```elixir

defmodule Admin.Repo do

  use Ecto.Repo, otp_app: :admin

  use Scrivener, page_size: 10

  defoverridable [update!: 2, update: 2, delete!: 2, delete: 2]

  def update(struct, opts \\ []) do

    #  ...

  end

  # ...

```

This is working. My update and delete functions work, but I'm getting compiler warnings

`warning: this clause cannot match because a previous clause at line 2 always matches`

What am I doing wrong?

Steve

[Paul Clegg]

I think Ecto.Repo already defines update, so when you redefine it, you get the warning.  If you don't want to use the original update, add "except: [update: 2]" to the use Ecto.Repo line (I think that works for use -- I know it works for import...)

...Paul

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[José Valim]

It is due to the optional arguments. Just remove them because Ecto has already defined those.

I also need to go on record and say that overriding functions that were not meant to be overridable is a really bad practice and I would avoid doing so. If you need to do paper trail, I would do changeset based operations or a way you can compose.

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José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

[Steve Pallen]

Thanks José.

Yes, I’m doing paper trail (not sure how you knew I was doing that LOL). Are you suggesting that I build 1 changeset that does the update and inserts a Version record? If so, can I do that without altering the original schema for the versioned model? Or are you suggesting that I add the Version insert in the controller’s update action.

Furthermore, I want to hook into the delete action to insert a Version record on delete. Normally, delete is called with the schema(model) and not a changeset.

Here is my Version schema:

```elixir
defmodule Whatwasit.Version do
use Ecto.Schema
import Ecto
import Ecto.Changeset

schema "versions" do
field :item_type, :string
field :item_id, :integer
field :action, :string # ~w(update delete)
field :object, :map # versioned schema stored as a map
field :whodoneit_name, :string # store name also to track if user is later deleted
belongs_to :whodoneit, Admin.User # TODO: need to get Admin.User from config
timestamps
end

def changeset(model, params \\ %{}) do
params = update_in params, [:object], &(Map.delete(&1, :__meta__) |> Map.delete(:__struct__))
model
|> cast(params, ~w(item_type item_id object whodoneit_id action whodoneit_name))
|> validate_required(~w(item_type item_id object)a)
end
end
```

Steve

[José Valim]

There is a function called prepare_changes or something similar in changesets that you could use to annotate any action. Although it should be also used sparingly, for this case it seems like the perfect solution.

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[Steve Pallen]

Yes, looks like just what I need. May also be able to use that from something I’m trying to solve with ExAdmin :)

Thanks José

[Steve Pallen]

Here is what I ended up with. 

https://github.com/smpallen99/whatwasit/blob/master/lib/whatwasit/schema.ex#L40

Thanks for your help José

Steve

[Steve Pallen]

José, so prepare_changes works well for update and delete actions. However, I would like to now hook into the insert action to create and link a new version record. But it looks like prepare_changes does not have access to the newly inserted schema (which is consistent with the docs saying its run before the database operation). Any suggestions how I hook into the repo operation after the insert so I can get access to it id?

[José Valim]

Unfortunately I don't have any. You would have to use Ecto.Multi but I am not sure if you want to convert to a Multi at this point.

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[Steve Pallen]

Thanks for the quick response José!!

So I guess I have two options:

1. Override insert functions in the repo which you already discouraged :)

2. Add an API to be used on the create action of the controller, to do the insert and Version insert. 

I’ll go with #2.

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[Michał Muskała]

On 31 Jul 2016, at 16:48, Steve Pallen <smpal...@gmail.com> wrote:

Thanks for the quick response José!!

So I guess I have two options:

1. Override insert functions in the repo which you already discouraged :)

2. Add an API to be used on the create action of the controller, to do the insert and Version insert. 

I’ll go with #2.

While overriding insert is probably not a good idea, providing something like insert_versioned that has the same interface as insert and manages the version would probably be quite a good API.

Michał.

[Steve Pallen]

Good idea. Thanks!!