Sinks

See Sinks for what a sink is and the storage backends Chronicle ships with. By default the client uses MongoDB, so most applications never need to think about sinks at all. You only configure a sink type when you want your read models stored somewhere else — for example, a SQL database.

Well-Known Sink Types

The WellKnownSinks constant exposes the sink types Chronicle ships with:

import { WellKnownSinks } from '@cratis/chronicle';

WellKnownSinks.MongoDB;   // 'MongoDB' — the default
WellKnownSinks.SQL;       // 'SQL'
WellKnownSinks.InMemory;  // 'InMemory'
WellKnownSinks.NotSet;    // 'NotSet' — no sink

A sink type identifier is just a string, so you can also pass the identifier of a custom sink registered in your Chronicle Kernel.

Configuring the Default Sink Type

The default sink type is configured on ChronicleOptions through defaultSinkTypeId. Every projection, reducer, and read model registered by the client uses this sink type unless overridden by the Kernel configuration.

When you don’t set it, it defaults to WellKnownSinks.MongoDB.

To persist read models into SQL instead, pass defaultSinkTypeId when creating the options:

import { ChronicleClient, ChronicleOptions, WellKnownSinks } from '@cratis/chronicle';

const options = ChronicleOptions.fromConnectionString(
    'chronicle://localhost:35000',
    { defaultSinkTypeId: WellKnownSinks.SQL });

const client = new ChronicleClient(options);

The same option works with the development factory:

import { ChronicleClient, ChronicleOptions, WellKnownSinks } from '@cratis/chronicle';

const options = ChronicleOptions.development({ defaultSinkTypeId: WellKnownSinks.SQL });
const client = new ChronicleClient(options);

Reading the Configured Sink Type

The configured value is available on the options as defaultSinkTypeId:

console.log(client.options.defaultSinkTypeId); // 'SQL'