dataPool() function

A connection pool whose arrays of enums and JSON columns can be read.

Signature:

export declare function dataPool(config: PoolConfig, parsers?: TypeParsers): Pool;

Parameters

Returns:

Pool

The pool.

Remarks

node-postgres parses a value by its type's oid, and it knows only the built-in ones. An enum is numbered when it is created, so its array type is numbered too, and neither number can be known ahead of time — the driver therefore hands back the literal text {EMAIL,SMS} where the ORM requires an array, and every read of the column fails with RUNTIME.DECODE_FAILED. A scalar enum is unaffected, because its text *is* its value.

So the oids are asked for, once, and those columns are parsed the way a text[] is — which is what an array of enums is on the wire. The JSON types are corrected at the same time, for the reason on .

The lookup is deferred to the first connection rather than done here, because a pool is built where a client is built and that is not a place where anything can be awaited. It runs once; a query that arrives while it is in flight waits for it rather than starting a second one.

The registry is the one the *runtime* reads, not the one a pool carries: the ORM passes its own types to every query, and that object falls through to pg-types for anything it does not handle itself. A parser set on the pool is therefore never consulted.

Three things follow from the registry being global. A raw pg query in the same process reads a JSON column as text and has to parse it itself, which is the trade for the ORM reading it correctly. An enum type created *after* the first connection is not picked up — which is a migration applied to a running process, and migrations run at start, before anything connects. And a process holding pools onto two different databases would have them share one numbering, which no service here does: a service owns one database.

Example

const db = postgres<Contract>({
    contractJson,
    pg: dataPool({ connectionString }),
});

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