Custom primary keys, it works?

[JanStevens]

Hello,

I see the readme stating that custom primary keys is still a work in progress but I managed to get it to work, my fear is that this is wrong and its not yet fully supported. Whats the current state of it?

Schema

  @primary_key {:uuid, :string, []}
  @derive {Phoenix.Param, key: :uuid}

  schema "device_configs" do
    field :environment, :string, default: "staging"
    field :configs, :map, default: %{}
    timestamps()
  end

Migration

    create_if_not_exists table(:device_configs, primary_key: false) do
      add :uuid, :string, primary_key: true
      add :environment, :string, default: "staging"
      add :configs, :map, default: %{}

      timestamps()
    end

DevicesEx.Repo.insert(%DevicesEx.DeviceConfig{uuid: "ACR001"})
{:ok,
 %DevicesEx.DeviceConfig{__meta__: #Ecto.Schema.Metadata<:loaded, "device_configs">,
  configs: %{}, environment: "staging",
  inserted_at: ~N[2016-12-18 15:50:21.840696],
  updated_at: ~N[2016-12-18 15:50:21.847592], uuid: "ACR001"}}
iex(5)> DevicesEx.Repo.all(query)
[debug] Selecting by match specification `[{{:device_configs, :"$1", :"$2", :"$3", :"$4", :"$5"}, [], [[:"$1", :"$2", :"$3", :"$4", :"$5"]]}]` with limit `nil`
[%DevicesEx.DeviceConfig{__meta__: #Ecto.Schema.Metadata<:built, "device_configs">,
  configs: %{}, environment: "staging",
  inserted_at: {{2016, 12, 18}, {15, 50, 21, 840696}},
  updated_at: {{2016, 12, 18}, {15, 50, 21, 847592}}, uuid: "ACR001"}]
iex(6)> DevicesEx.Repo.insert(%DevicesEx.DeviceConfig{uuid: "ACR001"})
** (CaseClauseError) no case clause matching: {:error, :already_exists}
    (ecto) lib/ecto/repo/schema.ex:459: Ecto.Repo.Schema.apply/4
    (ecto) lib/ecto/repo/schema.ex:198: anonymous fn/11 in Ecto.Repo.Schema.do_insert/4

[AndrewDryga]

Your example should work, but only because your primary key will be first in Mnesia record (and Mnesia triggers this field as PK).

[JanStevens]

Great thanks, and what would be the current limitations / possible issues?

[AndrewDryga]

Actually, I can't even guess :). Looks like it should work, but I have never tried this way. And in nearest future I will work on Ecto integrations tests to merge this PR elixir-ecto/ecto#1865, so can't tell when I will be able to get back to PK's.

[JanStevens]

Great ill keep you posted. And that looks awesome :D Great job!

[AndrewDryga]

Thanks for support and testing it :).

[JanStevens]

Allright, first issue that pops up during testing, I'm trying to test that the unique constraint is validated correctly. Kinda knew that it wouldn't work but here is the output I receive:

  1) test changeset validations with non unique uuid (DevicesEx.DeviceConfigTest)
     test/models/device_config_test.exs:20
     ** (CaseClauseError) no case clause matching: {:error, :already_exists}
     stacktrace:
       (ecto) lib/ecto/repo/schema.ex:459: Ecto.Repo.Schema.apply/4
       (ecto) lib/ecto/repo/schema.ex:198: anonymous fn/11 in Ecto.Repo.Schema.do_insert/4
       test/models/device_config_test.exs:23: (test)

It seems the error message from mnesia is not correctly translated to the upper layers

[AndrewDryga]

@JanStevens Can you give more code so I will be able to reproduce this? In meanwhile I have added new case that test insert with duplicate primary key.

[AndrewDryga]

Can you re-run tests against latest adapter version?

[JanStevens]

Hello,

Still same issue, I've setup a repo here with a working project (just run the tests): https://github.com/JanStevens/devices_ex

[kexoth]

Hello @AndrewDryga & @JanStevens

I'm migrating an app from Amnesia to this library, but have a similar issue.
I wanted to use a custom primary key & did as @JanStevens.
It worked at start, i.e. I can insert records & get them, also when I query directly :mnesia the results are as expected.

However I cannot update nor delete them. I get this error:

** (KeyError) key :struct not found in: []
     (elixir) lib/keyword.ex:333: Keyword.fetch!/2
       (ecto) lib/ecto/exceptions.ex:170: Ecto.NoPrimaryKeyValueError.exception/1
(ecto_mnesia) lib/ecto_mnesia/adapter.ex:265: Ecto.Mnesia.Adapter.get_pk!/2
(ecto_mnesia) lib/ecto_mnesia/adapter.ex:238: Ecto.Mnesia.Adapter.delete/4
       (ecto) lib/ecto/repo/schema.ex:459: Ecto.Repo.Schema.apply/4
       (ecto) lib/ecto/repo/schema.ex:352: anonymous fn/9 in Ecto.Repo.Schema.do_delete/4

I'm using :ecto_mnesia, "0.6.10". Doing the same operations directly with :mnesia work.

[scrogson]

However I cannot update nor delete them. I get this error:

I ran into that same error tonight. The error is being raised here. The KeyError is happening because the exception is supposed to be raised with the struct: module passed in.

The get_pk!/2 function will need to become get_pk!/3 and pass in the schema module so that it can be raised properly.

However, even after correcting the error in the source code locally, that didn't fix the error. I ended up needing to switch my options to the following in order to get it to work:

@primary_key {:uuid, :binary_id, autogenerate: true}

This seems like a bug to me. The code seems to be looking for a field that is autogenerated. Shouldn't the primary key be found with module.__schema__(:primary_key)?

[AndrewDryga]

@scrogson you are right, I'll fix it in next release.