Elixir: Saving a tuple in Postgres

You can sort of get it working - but should you?

I'm writing a Connect Four game application in Elixir. I wrote game logic which expects to receive the coordinates of a coin position as a tuple. Something like this {0, 1} would mean that the coin is in the first row and second column.

I am saving this information in my Postgres database but of course Postgres does not support the data structure of a tuple. Luckily, Stackoverflow came to the rescue and I learnt that Erlang has a function which converts a term to binary and back again. Great! I can save binary data in Postgres. I decided to convert the coordinates tuple to binary with :erlang.term_to_binary(coordinates) and save it in the database like that.

It works - but the more I'm working with this, the more I realise that this was not the best solution.

Debugging is harder

When I query the database to see which coordinates are saved, I see stuff like this:

connect_game_dev=# select * from moves;

 id | player |       coordinates        
 18 | red    | \x83680261016104         
 19 | red    | \x83680261006d0000000130 
 20 | red    | \x83680261006d0000000131 
(3 rows)

Not super useful when I want to find out if the right coordinates were created!

Input validation

Using Ecto changesets is slightly harder.

Ecto comes with various handy validation functions, for example validate_number. This function allows you to check if a number is greater or less than a specific value. Before saving the coordinates into the database, I want to make sure that the column number isn't less than 0 or more than the size of the game grid. And for rows, I could do a similar check. However, with my tuple data structure I'll need to write a custom validation function. It's possible, but using a provided function is much more convenient!

Improving my data storage

In the end I decided to change my database table and save the two coordinates separately instead. I created two new columns in my database, one for x_coordinate and one for y_coordinate. Each of those can save the coordinate integer. Now it's easy to see the coordinates in the database and I can make use of the validation function provided by Ecto!

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