Crate canton_pqs 

A typed read client for the Daml Participant Query Store (PQS, served by Scribe).

PQS streams a participant’s contracts into Postgres and exposes them through a small set of functions — active, creates, archives, exercises, lookup_contract. This crate reads them typed: a query names its template by type, and the row comes back as the generated payload.

No hand-written SQL, and no interpolation

Predicates compile to parameterized statements. Every caller-supplied value is a parameter, and so is every JSON field path — sent as text[] and applied with #>. The statement text depends on the shape of a query and never on its data, so a field name taken from user input is data Postgres never parses.

The payload is the same type the Ledger API gives you

PQS stores payloads in the Daml JSON encoding, which is what canton-daml implements — so a contract read here deserializes into the same generated type as one read from a transaction stream. That is the point of the crate: two ways in, one set of types.

Structs

Contract

A contract as PQS holds it: the typed payload, plus the ledger facts about it.

Exercise

An exercised choice as PQS holds it.

PqsClient

A read client for a PQS database.

Predicate

One condition on a contract’s payload or on its row.

Query

A query over one template, compiled to parameterized SQL.

Sql

A compiled statement: SQL with $n placeholders, and the values for them.

Enums

Op

How a value is compared.

Param

A parameter, in the form tokio-postgres will bind it.

Source

Which PQS function a query reads from.

Constants

DEFAULT_TIMEOUT

How long a connection attempt or a single query may take before it is reported as Error::Timeout instead of left hanging. See PqsClient::with_timeout.

Traits

IntoPath

Anything that names a path into the payload.

Functions

active_signed_by

Convenience: the active contracts of a template that a party signs.