Logging

It is possible to set up logs for all queries executed by Kysely using the log in the constructor.

There are 2 ways to configure it :

1. Pass an array with the log level

You can give an array of log levels to the log property in the Kysely constructor. The possible values are 'query' and 'error'.

const db = new Kysely({
  dialect: new PostgresDialect(postgresConfig),
  log: ['query', 'error']

2. Pass a function to the log property

Passing function to the Kysely constructor. The function will be called with a log event for each query executed.

The LogEvent interface looks like this :

interface LogEvent {
    level: 'query' | 'error';
    query: CompiledQuery;
    queryDurationMillis: number;
    error: unknown; // only present if level is 'error'
}

you can also use the function signature to have more flexibility on how you want to log the queries.

const db = new Kysely({
  dialect: new PostgresDialect(postgresConfig),
  log(event) {
    // you may want to log only the errored query :
    if (event.level === "error") {
        console.error("Query failed : ", {
          durationMs: event.queryDurationMillis,
          error: event.error,
          sql: event.query.sql,
          params: event.query.parameters,
        });
      }

    // or log all queries :
    console.log("Query executed : ", {
      durationMs: event.queryDurationMillis,
      sql: event.query.sql,
      params: event.query.parameters,
    });
  }
})

For more information check the docs for details on the interfaces KyselyConfig.