DB::Serializable with JOIN?

Help & Support
1

I’m trying to use DB::Serializable to deserialize rows from a Postgres DB into Crystal objects. It works great when a row maps to a single object, but I can’t seem to get it to map to multiple objects:

db.query_all <<-SQL, app_id, as: {App, User}
  SELECT apps.*, users.* -- I specify the columns explicitly but it would just be noise here
  FROM apps
    JOIN app_access ON app_access.app_id = apps.id
    JOIN users ON app_access.user_id = users.id
  WHERE apps.id = $1
SQL

Is there a way to get crystal-db to chop up a result row into two or more different objects?

2

I do this with neo4j like this:

txn.exec_cast <<-CYPHER, {app_id: app_id}, {App, User}
  MATCH (user:User)-[:GRANTED_ACCESS_TO]->(app:App)
  WHERE app.id = $app_id
  RETURN app, user
CYPHER

But with SQL, an ORM has to chop up the row into whole objects. It seems DB::Serializable has enough information to do this, I just don’t know how to invoke that.

3

Db Serializable is very basic: just fetch from a single table. No joins, no nothing. I recommend you use a proper ORM. Maybe we should deprecate and remove serializable because it’s a bit useless.

1 Like
4

You might use include JSON::Serializable, <class>.to_json and <class>.from_json; and then try saving your deserialize objects.