acrolink

How to set id value in code upon entity creation

I have a special need to set the id of newly created entities to some integer relating to UNIX timestamp (not autoincrement based). Any idea how to do this? i am using Phoenix 1.3. Thank you.

19 comments

/phoenix #changesets

0 10224 19

2017-11-10 09:31:00 UTC

Marked As Solved

voger

Hello. Here is the example repo. GitHub - voger/custom_id_test: example phoenix project for custom ids · GitHub
It took me a while to make the pgsql function work and I didn’t have much time to add controllers or example of custom id using changesets. This example demonstrates how to do it using the database with a sequence as in the link from tomconry. Take a look at the migration.

To use it after you clone it in your computer and do the migrations run iex -S mix and try

iex(1)> alias CustomIdTest.Context
CustomIdTest.Context
iex(2)> Context.create_entry(%{entry: "Reandom text"})
[debug] QUERY OK db=28.5ms queue=0.2ms
INSERT INTO "entry_fragment" ("entry") VALUES ($1) ["Reandom text"]
{:ok,
 %CustomIdTest.EntryFragment{__meta__: #Ecto.Schema.Metadata<:loaded, "entry_fragment">,
  entry: "Reandom text", id: nil}}
iex(3)> Context.get_entries
[debug] QUERY OK source="entry_fragment" db=4.6ms decode=18.1ms queue=0.2ms
SELECT e0."id", e0."entry" FROM "entry_fragment" AS e0 []
[%CustomIdTest.EntryFragment{__meta__: #Ecto.Schema.Metadata<:loaded, "entry_fragment">,
  entry: "random", id: 1616258530136822785},
 %CustomIdTest.EntryFragment{__meta__: #Ecto.Schema.Metadata<:loaded, "entry_fragment">,
  entry: "random", id: 1616258765361779714},
 %CustomIdTest.EntryFragment{__meta__: #Ecto.Schema.Metadata<:loaded, "entry_fragment">,
  entry: "Reandom text", id: 1616264079603667971}]

Update:
@acrolink
I added another example on how to set the id from the changeset. This time I used a generator to speed up and you can see the results in a browser. I probably messed up naming and spelling because it was done in a hurry. I hope it doesn’t mind.

To use it go to http://localhost:4000/things_with_changeset

Especially interesting I believe are [the migration] (custom_id_test/priv/repo/migrations/20171002055049_create_things_with_changeset.exs at master · voger/custom_id_test · GitHub ) and the schema

I modified the controller with this line alias CustomIdTest.CustomIdTest, as: CIT and renamed the relevant function calls. This is irrelevant to the problem at hand. I only did this because I messed up the naming. You don’t have to do this in your controllers.

It is not a well thought example but I hope it helps.

Post #12

Also Liked

tomconroy

Try doing it with a Postgres function, like this

http://rob.conery.io/2014/05/28/a-better-id-generator-for-postgresql/

Post #4

idi527

Sorry, I’ve probably confused you …

The example with defstruct that I’ve provided seems to not be what you want. I just wondered if you were asking about ecto or elixir structs.

Judging by the error you get, you were asking about ecto.

To get custom ids you should use @primary_key.

Post #3

voger

@idi527: Sorry, I accidentally hit reply in your post. This reply was meant for the original post.

If your question is about how to do custom primary keys with Ecto then here is a guide in phoenix blog
http://phoenixframework.org/blog/custom-primary-key

Post #5

Last Post!

voger

Hello. I don’t have access to elixir right now so I can’t test what I say is accurate. Anyway here is my attempt

If you need autoincrementing bigint you may not need to do anything. [According to the docs]
(https://hexdocs.pm/ecto/Ecto.Migration.html#content)

:migration_primary_key - Ecto uses the :id column with type :bigserial but you can configure it via:
config :app, App.Repo, migration_primary_key: [id: :uuid, type: :binary_id]

So it seems Ecto already uses an autoincrementing bigint as an :id. Not the full range. Only the positive values

If for some reason you don’t want autoincrementing values then you do this in your schema

 def change do

    create table(:books, primary_key: false) do
      add :id, :bigint, primary_key: true
      add :title, :string

      timestamps()
    end

but now you have to handle the key yourself.

Again, I can’t test the accuracy of the above.

Post #19