Projections

Reading one projection, and deleting projections in bulk. Projections are written with POST /write. What a projection is, and how versions work, is in Concepts: Projections.

Reading a projection#

curl -i http://127.0.0.1:8085/projections/user-profile/123

HTTP/1.1 200 OK
Content-Type: text/plain; charset=utf-8
X-Tamarackdb-Version: 9f3c2a1e-7b4d-4c8e-a5f6-0d1e2f3a4b5c
X-Tamarackdb-Store: 5b0c7e2a-1f4d-4a9b-8c3e-6d2f1a0b9e47

{"name":"Ada Lovelace"}

• 200 OK: the body is the payload exactly as written, with no JSON envelope around it, since its format is up to the writing application. The version is in the X-Tamarackdb-Version header: keep it to replace or delete the projection later.
• 404 ProjectionNotFound: no projection exists at that type + id. This is an ordinary answer, not a failure: a projector that gets a 404 usually creates the projection.
• Both carry the store ID in the X-Tamarackdb-Store header.
• The read sees committed projections only, and never waits for a write.
• type and id are path segments, so they’re percent-encoded: an id of a/b is /projections/user-profile/a%2Fb, and a space is %20. The same goes for DELETE /projections/{type}.

Bulk delete#

curl -X DELETE http://127.0.0.1:8085/projections/user-profile
curl -X DELETE http://127.0.0.1:8085/projections

• DELETE /projections/{type} deletes every projection of one type. DELETE /projections deletes every projection. Both respond 204 No Content.
• Neither takes a version: they’re meant for a rebuild, and never report a conflict.
• Both wait for their turn like a write (see Writing):
  • a write queued before the delete goes through first, and the delete then removes what it wrote;
  • a later write that replaces or deletes a projection the delete removed gets 409;
  • a delete can get 503 WriteQueueFull;
  • closing the connection while it waits takes it out of the queue, with nothing deleted.
• The store ID doesn’t change.