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.None;      // 'None' — no sink

A sink type identifier is 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. The client registers every active projection, reducer, and read model with this sink type. A passive projection is registered with WellKnownSinks.None instead.

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

To persist read models into SQL instead, pass defaultSinkTypeId when creating the options. The kernel must have SQL read-model storage configured; see Sinks.

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'