LanguageExternal tables

External tables

An external table lives outside the document: in another service, or another database. Declare it so that references to it are checked and drawn like any other.

orders.erdOpen in playground
external table users "Accounts service" {
  id  bigint  pk
}

table orders {
  id       bigint  pk
  user_id  bigint  ~> users
}
The diagram resin draws for orders.erdThe diagram resin draws for orders.erd

What to list

List only the columns you point at, usually the primary key. An external table receives references and is checked like any other table, with two limits:

  • its columns cannot hold references (-> or ~>);
  • it cannot have audit.

A reference into another service usually has no database constraint behind it, so it is written ~>, a logical reference. Put the external table in a service block named after that service, and the diagram shows where the service boundary is.

In the diagram

External tables have a dashed border and an EXTERNAL tag.

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