Reading from a stream

When using EventStoreDB it's possible to read events from a given stream.

Reading forwards

The simplest way to read a stream forwards is to supply a stream name, direction and revision to start from. This can either be a stream position Start or a an big int (unsigned 64 bit integer):

var events = client.ReadStreamAsync(
	Direction.Forwards,
	"some-stream",
	StreamPosition.Start);

const events = await client.readStream("some-stream", 10, {
  direction: FORWARDS,
  fromRevision: START,
});

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This will return an enumerable that can be iterated on:

await foreach (var @event in events) {
	Console.WriteLine(Encoding.UTF8.GetString(@event.Event.Data.ToArray()));
}

for (var resolvedEvent of events) {
  console.log(resolvedEvent.event.data);
}

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There are a number of additional arguments you can provide when reading a stream

maxCount

Passing in the max count allows you to limit the number of events that returned.

resolveLinkTos

When using projections to create new events you can set whether the generated events are pointers to existing events. Setting this value to true will tell EventStoreDB to return the event as well as the event linking to it.

configureOperationOptions

This argument is generic setting class for all operations that can be set on all operations executed against EventStoreDB.

userCredentials

The credentials used to read the data can be supplied. to be used by the subscription as follows. This will override the default credentials set on the connection.

var result = client.ReadStreamAsync(
    Direction.Forwards,
    "some-stream",
    StreamPosition.Start,
    userCredentials: new UserCredentials("admin", "changeit"),
    cancellationToken: cancellationToken);

const credentials = {
  username: "admin",
  password: "changeit",
};
const events = await client.readStream("some-stream", 10, {
  direction: FORWARDS,
  fromRevision: START,
  credentials,
});

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Reading from a revision

As well as providing a StreamPosition you can also provide a specific stream revision in the form of a big int (unsigned 64 bit integer).

var events = client.ReadStreamAsync(
	Direction.Forwards,
	"some-stream",
	revision: 10,
	maxCount: 20);

const events = await client.readStream("some-stream", 20, {
  direction: FORWARDS,
  fromRevision: BigInt(10),
});

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Reading backwards

As well as being able to read a stream forwards you can also go backwards. When reading backwards is the stream position will have to be set to the end if you want to read all the events:

var events = client.ReadStreamAsync(
	Direction.Backwards,
	"some-stream",
	StreamPosition.End);

await foreach (var e in events) {
	Console.WriteLine(Encoding.UTF8.GetString(e.Event.Data.ToArray()));
}

const events = await client.readStream("some-stream", 10, {
  direction: BACKWARDS,
  fromRevision: END,
});

for (var resolvedEvent of events) {
  console.log(resolvedEvent.event.data);
}

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TIP

You can use reading backwards to find the last position in the stream. Just read backwards one event and get the position.

Checking for stream presence

Reading a stream returns a ReadStreamResult this contains a property ReadState. This property can have the value StreamNotFound and Ok.

It is important to check the value of this field before attempting to iterate an empty stream as it will throw an exception. For example.

var result = client.ReadStreamAsync(
	Direction.Forwards,
	"some-stream",
	revision: 10,
	maxCount: 20);

if (await result.ReadState == ReadState.StreamNotFound) {
	return;
}

await foreach (var e in result) {
	Console.WriteLine(Encoding.UTF8.GetString(e.Event.Data.ToArray()));
}

let events = [];
try {
  events = await client.readStream("some-stream", 20, {
    direction: FORWARDS,
    fromRevision: BigInt(10),
  });
} catch (error) {
  if (error.type == ErrorType.STREAM_NOT_FOUND) return;

  throw error;
}

for (var resolvedEvent of events) {
  console.log(resolvedEvent.event.data);
}

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