A typed C# predicate on generated types, and the Postgres it becomes

[monsieurleberre]

One thing I find handy in the SDK: the type you submit with is the type you query with. Canton.Ledger.Pqs.Client takes a C# expression over the generated bindings and compiles it into a parameterized predicate on PQS's payload JSON.

Here is a query against the Token Standard V2 demo's Asset template (generated by dpm codegen-cs), run on a local LocalNet 0.9.1-1 with PQS:

var assets = await pqs.QueryAsync<Asset>(
    Filter.Where<Asset>(a => a.Name == "GOLD" && a.Amount >= 10m),
    new PqsPage(limit: 3));

With Npgsql logging switched on, this is the statement that went to Postgres:

SELECT contract_id, payload FROM active($1)
WHERE (payload->>'name' = $2 AND (payload->>'amount')::numeric >= $3)
ORDER BY contract_id LIMIT $4 OFFSET $5
-- $1 = canton-mini-demo-h03254a5ede8d:MiniDemo.Asset:Asset, $2 = GOLD, $3 = 10, $4 = 3, $5 = 0

And the rows, decoded back into Asset:

001d116b… GOLD 42.0000000000
00745cf4… GOLD 10.0000000000
00c7ad77… GOLD 42.0000000000

The field names come from the generated record, so a rename in Daml is a compile error rather than a silent empty result. Values are always parameters, and Amount >= 10m is cast to numeric because the compiler knows the field is a Daml Numeric.

The client does not expose the SQL itself, so I read it from Npgsql's debug log via a registered NpgsqlDataSource. Comparisons, nested records, Optional, lists and maps are supported; the PQS client README lists them.

Tell us which predicates you'd like to see next.