How can I set castDecimalToDouble in duckdb-wasm

Question

I'm using duckdb-wasm to read parquet files containing decimal values. How can I have duckdb have the converted to double automatically? I have found this documentation, but don't know how to apply it:

https://shell.duckdb.org/docs/interfaces/index.DuckDBQueryConfig.html#castDecimalToDouble

Answer 1

The DuckDBQueryConfig interface you've found is used as the type of the input parameter to AsyncDuckDB.open used to provide configuration options when opening a new DuckDB database.

This is a full example of fetching the bundles from jsDelivr, instantiating the worker, logger, and an AsyncDuckDB binding. The code then opens a new database with the configuration options to do the casting.

import * as duckdb from '@duckdb/duckdb-wasm';

export async function init(): Promise<duckdb.AsyncDuckDB> {
  const JSDELIVR_BUNDLES = duckdb.getJsDelivrBundles();

  const bundle: duckdb.DuckDBBundle = await duckdb.selectBundle(
      JSDELIVR_BUNDLES
  );

  const worker_url = URL.createObjectURL(
    new Blob([`importScripts("${bundle.mainWorker!}");`], {
      type: 'text/javascript',
    })
  );

  const worker = new Worker(worker_url);

  const logger = new duckdb.ConsoleLogger();
  const db = new duckdb.AsyncDuckDB(logger, worker);
  await this.db.instantiate(bundle.mainModule, bundle.pthreadWorker);
  URL.revokeObjectURL(worker_url);

  await db.open({
    query: { castBigIntToDouble: true, castDecimalToDouble: true },
  });

  return db;
}