Multitenancy support

SAP Cloud Platform CF offers the possibility to develop multitenancy applications and CAP has built in support.

• https://cap.cloud.sap/docs/guides/multitenancy#how-it-works
• https://help.sap.com/viewer/65de2977205c403bbc107264b8eccf4b/Cloud/en-US/5e8a2b74e4f2442b8257c850ed912f48.html
• https://blogs.sap.com/2020/08/20/getting-your-head-into-cloud-application-programming-model-multitenancy/

When running on SAP CF, the PostgreSQL adapter should be able to handle the multitenancy. I am currently not sure about all the requirements, but one is to change the schema based on the requests tenant. A possible solution could like this:

class PostgresDatabase extends cds.DatabaseService {
...

  async acquire(arg) {

    // fetch the tenant if available
    const tenant = (typeof arg === 'string' ? arg : arg.user.tenant) || 'anonymous'

    // define the used schema, maybe add some more advanced naming logic
    const schema = tenant === 'anonymous' ? 'public' : tenant;

    // change the PostgreSQL schema for the client
    this._pool.on('connect', (client) => {

      // search_path also supports naming multiple schemas so things can be split across schemas (provider, subscribers)
      client.query(`SET search_path TO ${schema};`)
    })

    const dbc = await this._pool.connect()
    return dbc
  }

...
}

For a future implementation it would be necessary to identify all the internal requirements by analyzing the cds core and come up with a concept for PostgreSQL (that maybe works for other DB adapters as well).

[austinkloske22]

why don’t you put this in a PR? all contributions are welcome!

1st open source PR created! https://github.com/sapmentors/cds-pg/pull/113 - Please let me know if I need to do anything differently next time.

[austinkloske22]

I think that multitenant support will need to be implemented in the cds-dbm module.

I would like to add a multitenant flag and tenant array in the migration options. If the multitenant flag = true, then we also deploy to tenant schemas. Problem is I don’t know how to proberly implement & test this feature yet.