Projection management

The various gRPC client APIs include dedicated clients that allow you to manage projections.

WARNING

Currently not all clients fully expose all operations.

For a detailed explanation of projections, see the server documentation.

You can find the full sample code from this documentation page in the respective clients repositoriesopen in new window.

Required packages

Install the client SDK package to your project.

dotnet add package EventStore.Client.Grpc.ProjectionManagement --version 21.*

// This is currently not available in the Go client

# Maven
<dependency>
  <groupId>com.eventstore</groupId>
  <artifactId>db-client-java</artifactId>
  <version>1.0.0</version>
</dependency>

# Gradle
implementation 'com.eventstore:db-client-java:1.0.0'

# SBT
libraryDependencies += "com.eventstore" % "db-client-java" % "1.0.0"

1
2
3
4
5
6
7
8
9
10
11
12

# Yarn
$ yarn add @eventstore/db-client

# NPM
$ npm install --save @eventstore/db-client

1
2
3
4
5

No additional configuration is needed having Rust installed. Go check https://rustup.rs.

# TypeScript Declarations are included in the package.

# Yarn
$ yarn add @eventstore/db-client

# NPM
$ npm install --save @eventstore/db-client

1
2
3
4
5
6
7

Creating a client

Projection management operations are exposed through a dedicated client.

var settings = EventStoreClientSettings.Create(connection);
settings.ConnectionName = "Projection management client";
settings.DefaultCredentials = new UserCredentials("admin", "changeit");
var managementClient = new EventStoreProjectionManagementClient(settings);

1
2
3
4

// This is currently not available in the Go client

Sample available soon

const client = EventStoreDBClient.connectionString`
    esdb+discover://${ADMIN}:${PASSWORD}@${ENDPOINT}?nodePreference=leader
`;

1
2
3

Sample available soon

const client = EventStoreDBClient.connectionString`
    esdb+discover://${ADMIN}:${PASSWORD}@${ENDPOINT}?nodePreference=leader
`;

1
2
3

Create a projection

Creates a projection that runs until the last event in the store, and then continues processing new events as they are appended to the store. The query parameter contains the JavaScript you want created as a projection. Projections have explicit names, and you can enable or disable them via this name.

const string js = @"fromAll()
                    .when({
                        $init: function() {
                            return {
                                count: 0
                            };
                        },
                        $any: function(s, e) {
                            s.count += 1;
                        }
                    })
                    .outputState();";
var name = quot;countEvents_Create_{Guid.NewGuid()}";
await managementClient.CreateContinuousAsync(name, js);

1
2
3
4
5
6
7
8
9
10
11
12
13
14

// This is currently not available in the Go client

Sample available soon

const name = `countEvents_Create_${uuid()}`;
const projection = `
    fromAll()
        .when({
            $init() {
                return {
                    count: 0,
                };
            },
            $any(s, e) {
                s.count += 1;
            }
        })
        .outputState();
`;
await client.createProjection(name, projection);

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

// This is currently not available in the Rust client

const name = `countEvents_Create_${uuid()}`;
const projection = `
    fromAll()
        .when({
            $init() {
                return {
                    count: 0,
                };
            },
            $any(s, e) {
                s.count += 1;
            }
        })
        .outputState();
`;
await client.createProjection(name, projection);

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

Trying to create projections with the same name will result in an error:

await managementClient.CreateContinuousAsync(name, js);
try {

    await managementClient.CreateContinuousAsync(name, js);
} catch (RpcException e) when (e.StatusCode is StatusCode.AlreadyExists) {
    Console.WriteLine(e.Message);
} catch (RpcException e) when (e.Message.Contains("Conflict")) {  // will be removed in a future release
    var format = quot;{name} already exists";
    Console.WriteLine(format);
}

1
2
3
4
5
6
7
8
9
10

// This is currently not available in the Go client

Sample available soon

try {
  await client.createProjection(name, projection);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("Conflict")) throw err;
  console.log(`${name} already exists`);
}

1
2
3
4
5
6

// This is currently not available in the Rust client

try {
  await client.createProjection(name, projection);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("Conflict")) throw err;
  console.log(`${name} already exists`);
}

1
2
3
4
5
6

Restart the subsystem

Restarts the entire projection subsystem. The user must be in the $ops or $admin group to perform this operation

await managementClient.RestartSubsystemAsync();

// This is currently not available in the Go client

// This is currently not available in the java client

await client.restartSubsystem();

Sample available soon

await client.restartSubsystem();

Enable a projection

Enables an existing projection by name. Once enabled, the projection will start to process events even after restarting the server or the projection subsystem. You must have access to a projection to enable it, see the ACL documentation

await managementClient.EnableAsync("$by_category");

// This is currently not available in the Go client

// This is currently not available in the java client

await client.enableProjection("$by_category");

// This is currently not available in the Rust client

await client.enableProjection("$by_category");

You can only enable an existing projection. When you try to enable a non-existing projection, you'll get an error:

try {
    await managementClient.EnableAsync("projection that does not exists");
} catch (RpcException e) when (e.StatusCode is StatusCode.NotFound) {
    Console.WriteLine(e.Message);
} catch (RpcException e) when (e.Message.Contains("NotFound")) {  // will be removed in a future release
    Console.WriteLine(e.Message);
}

1
2
3
4
5
6
7

// This is currently not available in the Go client

// This is currently not available in the java client

const projectionName = "projection that does not exist";

try {
  await client.enableProjection(projectionName);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

// This is currently not available in the Rust client

const projectionName = "projection that does not exist";

try {
  await client.enableProjection(projectionName);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

Disable a projection

Disables a projection, this will save the projection checkpoint. Once disabled, the projection will not process events even after restarting the server or the projection subsystem. You must have access to a projection to disable it, see the ACL documentation

WARNING

The .net clients up to version 21.2 had an incorrect behavior: they will not save the checkpoint

await managementClient.DisableAsync("$by_category");

// This is currently not available in the Go client

// This is currently not available in the java client

await client.disableProjection("$by_category");

// This is currently not available in the Rust client

await client.disableProjection("$by_category");

You can only disable an existing projection. When you try to disable a non-existing projection, you'll get an error:

try {
    await managementClient.DisableAsync("projection that does not exists");
} catch (RpcException e) when (e.StatusCode is StatusCode.NotFound) {
    Console.WriteLine(e.Message);
} catch (RpcException e) when (e.Message.Contains("NotFound")) {  // will be removed in a future release
    Console.WriteLine(e.Message);
}

1
2
3
4
5
6
7

// This is currently not available in the Go client

// This is currently not available in the java client

const projectionName = "projection that does not exist";

try {
  await client.disableProjection(projectionName);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

// This is currently not available in the Rust client

const projectionName = "projection that does not exist";

try {
  await client.disableProjection(projectionName);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

Delete a projection

Deletes a projection

// This is currently not available in the .net client

// This is currently not available in the Go client

// This is currently not available in the java client

// A projection must be disabled to allow it to be deleted.
await client.disableProjection(name);

// The projection can now be deleted
await client.deleteProjection(name);

1
2
3
4
5

// This is currently not available in the Rust client

// A projection must be disabled to allow it to be deleted.
await client.disableProjection(name);

// The projection can now be deleted
await client.deleteProjection(name);

1
2
3
4
5

You can only delete an existing projection. When you try to delete a non-existing projection, you'll get an error:

// This is currently not available in the .net client

// This is currently not available in the Go client

// This is currently not available in the java client

const projectionName = "projection that does not exist";

try {
  await client.deleteProjection(projectionName);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

// This is currently not available in the Rust client

const projectionName = "projection that does not exist";

try {
  await client.deleteProjection(projectionName);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

Abort a projection

Aborts a projection, this will not save the projection's checkpoint.

WARNING

The .net clients up to version 21.2 had an incorrect behavior: they will save the checkpoint.

// The .net clients prior to version 21.6 had an incorrect behavior: they will save the checkpoint.
await managementClient.AbortAsync("countEvents_Abort");

1
2

// This is currently not available in the Go client

// This is currently not available in the java client

await client.abortProjection(name);

// This is currently not available in the Rust client

await client.abortProjection(name);

You can only abort an existing projection. When you try to abort a non-existing projection, you'll get an error:

try {
    await managementClient.AbortAsync("projection that does not exists");
} catch (RpcException e) when (e.StatusCode is StatusCode.NotFound) {
    Console.WriteLine(e.Message);
} catch (RpcException e) when (e.Message.Contains("NotFound")) {  // will be removed in a future release
    Console.WriteLine(e.Message);
}

1
2
3
4
5
6
7

// This is currently not available in the Go client

// This is currently not available in the java client

const projectionName = "projection that does not exist";

try {
  await client.abortProjection(projectionName);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

// This is currently not available in the Rust client

const projectionName = "projection that does not exist";

try {
  await client.abortProjection(projectionName);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

Reset a projection

Resets a projection. This will re-emit events. Streams that are written to from the projection will also be soft deleted.

// Checkpoint will be written prior to resetting the projection
await managementClient.ResetAsync("countEvents_Reset");

1
2

// This is currently not available in the Go client

// This is currently not available in the java client

await client.resetProjection(name);

// This is currently not available in the Rust client

await client.resetProjection(name);

Resetting a projection that does not exist will result in an error.

try {
    await managementClient.ResetAsync("projection that does not exists");
} catch (RpcException e) when (e.StatusCode is StatusCode.NotFound) {
    Console.WriteLine(e.Message);
} catch (RpcException e) when (e.Message.Contains("NotFound")) {  // will be removed in a future release
    Console.WriteLine(e.Message);
}

1
2
3
4
5
6
7

// This is currently not available in the Go client

// This is currently not available in the java client

const projectionName = "projection that does not exist";

try {
  await client.resetProjection(projectionName);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

// This is currently not available in the Rust client

const projectionName = "projection that does not exist";

try {
  await client.resetProjection(projectionName);
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

Update a projection

Updates a projection. The name parameter is the name of the projection to be updated. The query parameter contains the new JavaScript.

const string js = @"fromAll()
                    .when({
                        $init: function() {
                            return {
                                count: 0
                            };
                        },
                        $any: function(s, e) {
                            s.count += 1;
                        }
                    })
                    .outputState();";
var name = quot;countEvents_Update_{Guid.NewGuid()}";

await managementClient.CreateContinuousAsync(name, "fromAll().when()");
await managementClient.UpdateAsync(name, js);

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

// This is currently not available in the Go client

// This is currently not available in the java client

const name = `countEvents_Update_${uuid()}`;
const projection = `
    fromAll()
        .when({
            $init() {
                return {
                    count: 0,
                };
            },
            $any(s, e) {
                s.count += 1;
            }
        })
        .outputState();
`;
await client.createProjection(name, "fromAll().when()");
await client.updateProjection(name, projection);

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

// This is currently not available in the Rust client

const name = `countEvents_Update_${uuid()}`;
const projection = `
    fromAll()
        .when({
            $init() {
                return {
                    count: 0,
                };
            },
            $any(s, e) {
                s.count += 1;
            }
        })
        .outputState();
`;
await client.createProjection(name, "fromAll().when()");
await client.updateProjection(name, projection);

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

You can only update an existing projection. When you try to update a non-existing projection, you'll get an error:

try {
    await managementClient.UpdateAsync("Update Not existing projection", "fromAll().when()");
} catch (RpcException e) when (e.StatusCode is StatusCode.NotFound) {
    Console.WriteLine(e.Message);
} catch (RpcException e) when (e.Message.Contains("NotFound")) {  // will be removed in a future release
    Console.WriteLine("'Update Not existing projection' does not exists and can not be updated");
}

1
2
3
4
5
6
7

// This is currently not available in the Go client

// This is currently not available in the java client

const projectionName = "projection that does not exist";

try {
  await client.updateProjection(projectionName, "fromAll().when()");
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

// This is currently not available in the Rust client

const projectionName = "projection that does not exist";

try {
  await client.updateProjection(projectionName, "fromAll().when()");
} catch (err) {
  if (!isCommandError(err) || !err.message.includes("NotFound")) throw err;
  console.log(`${projectionName} does not exist`);
}

1
2
3
4
5
6
7
8

List all projections

Returns a list of all projections, user defined & system projections. See the projection details section for an explanation of the returned values

var details = managementClient.ListAllAsync();
await foreach (var detail in details) {
    Console.WriteLine(
        $@"{detail.Name}, {detail.Status}, {detail.CheckpointStatus}, {detail.Mode}, {detail.Progress}");
}

1
2
3
4
5

// This is currently not available in the Go client

// This is currently not available in the java client

// This is currently not available in the nodejs client

// This is currently not available in the Rust client

// This is currently not available in the nodejs client

List continuous projections

Returns a list of all continuous projections. See the projection details section for an explanation of the returned values

var details = managementClient.ListContinuousAsync();
await foreach (var detail in details) {
    Console.WriteLine(
        $@"{detail.Name}, {detail.Status}, {detail.CheckpointStatus}, {detail.Mode}, {detail.Progress}");
}

1
2
3
4
5

// This is currently not available in the Go client

// This is currently not available in the java client

const projections = await client.listProjections();

for (const { name, status, checkpointStatus, progress } of projections) {
  console.log(name, status, checkpointStatus, progress);
}

1
2
3
4
5

// This is currently not available in the Rust client

const projections = await client.listProjections();

for (const { name, status, checkpointStatus, progress } of projections) {
  console.log(name, status, checkpointStatus, progress);
}

1
2
3
4
5

Get Status

Gets the status of a named projection. See the projection details section for an explanation of the returned values

await managementClient.CreateContinuousAsync(name, js);
var status = await managementClient.GetStatusAsync(name);
Console.WriteLine(
    $@"{status?.Name}, {status?.Status}, {status?.CheckpointStatus}, {status?.Mode}, {status?.Progress}");

1
2
3
4

// This is currently not available in the Go client

// This is currently not available in the java client

const projection = await client.getProjectionStatus(name);

console.log(
  projection.name,
  projection.status,
  projection.checkpointStatus,
  projection.progress
);

1
2
3
4
5
6
7
8

// This is currently not available in the Rust client

const projection = await client.getProjectionStatus(name);

console.log(
  projection.name,
  projection.status,
  projection.checkpointStatus,
  projection.progress
);

1
2
3
4
5
6
7
8

Get state

Retrieves the state of a projection.

Sample available soon

// This is currently not available in the Go client

// This is currently not available in the java client

const name = `get_state_example`;
const projection = `
    fromAll()
        .when({
            $init() {
                return {
                    count: 0,
                };
            },
            $any(s, e) {
                s.count += 1;
            }
        })
        .transformBy((state) => state.count)
        .outputState();
`;

await client.createProjection(name, projection);

// Give it some time to count event
await delay(500);

const state = await client.getProjectionState(name);

console.log(`Counted ${state.count} events.`);

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

// This is currently not available in the Rust client

interface CountProjectionState {
  count: number;
}

const name = `get_state_example`;
const projection = `
    fromAll()
        .when({
            $init() {
                return {
                    count: 0,
                };
            },
            $any(s, e) {
                s.count += 1;
            }
        })
        .transformBy((state) => state.count)
        .outputState();
`;

await client.createProjection(name, projection);

// Give it some time to count event
await delay(500);

const state = await client.getProjectionState<CountProjectionState>(name);

console.log(`Counted ${state.count} events.`);

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29

Get result

Retrieves the result of the named projection and partition.

const string js = @"fromAll()
                    .when({
                        $init: function() {
                            return {
                                count: 0
                            };
                        },
                        $any: function(s, e) {
                            s.count += 1;
                        }
                    })
                    .outputState();";
var name = quot;countEvents_Result_{Guid.NewGuid()}";

await managementClient.CreateContinuousAsync(name, js);
await Task.Delay(500);  //give it some time to have a result.

// Results are retrieved either as  JsonDocument or a typed result 
var document = await managementClient.GetResultAsync(name);
var result = await managementClient.GetResultAsync<Result>(name);

Console.WriteLine(DocToString(document));
Console.WriteLine(result);

static string DocToString(JsonDocument d) {
    using var stream = new MemoryStream();
    using Utf8JsonWriter writer = new Utf8JsonWriter(stream, new JsonWriterOptions { Indented = false });
    d.WriteTo(writer);
    writer.Flush();
    return Encoding.UTF8.GetString(stream.ToArray());
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31

// This is currently not available in the Go client

Sample available soon

const name = `get_result_example`;
const projection = `
    fromAll()
        .when({
            $init() {
                return {
                    count: 0,
                };
            },
            $any(s, e) {
                s.count += 1;
            }
        })
        .transformBy((state) => state.count)
        .outputState();
`;

await client.createProjection(name, projection);

// Give it some time to have a result.
await delay(500);

const result = await client.getProjectionResult(name);

console.log(`Counted ${result} events.`);

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

// This is currently not available in the Rust client

const name = `get_result_example`;
const projection = `
    fromAll()
        .when({
            $init() {
                return {
                    count: 0,
                };
            },
            $any(s, e) {
                s.count += 1;
            }
        })
        .transformBy((state) => state.count)
        .outputState();
`;

await client.createProjection(name, projection);

// Give it some time to have a result.
await delay(500);

const result = await client.getProjectionResult<number>(name);

console.log(`Counted ${result} events.`);

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

Projection Details

List all, list continuous and get status all return the details and statistics of projections

Field	Description
`Name`, `EffectiveName`	The name of the projection
`Status`	A human readable string of the current statuses of the projection (see below)
`StateReason`	A human readable string explaining the reason of the current projection state
`CheckpointStatus`	A human readable string explaining the current operation performed on the checkpoint : `requested`, `writing`
`Mode`	`Continuous`, `OneTime` , `Transient`
`CoreProcessingTime`	The total time, in ms, the projection took to handle events since the last restart
`Progress`	The progress, in %, indicates how far this projection has processed event, in case of a restart this could be -1% or some number. It will be updated as soon as a new event is appended and processed
`WritesInProgress`	The number of write requests to emitted streams currently in progress, these writes can be batches of events
`ReadsInProgress`	The number of read requests currently in progress
`PartitionsCached`	The number of cached projection partitions
`Position`	The Position of the last processed event
`LastCheckpoint`	The Position of the last checkpoint of this projection
`EventsProcessedAfterRestart`	The number of events processed since the last restart of this projection
`BufferedEvents`	The number of events in the projection read buffer
`WritePendingEventsBeforeCheckpoint`	The number of events waiting to be appended to emitted streams before the pending checkpoint can be written
`WritePendingEventsAfterCheckpoint`	The number of events to be appended to emitted streams since the last checkpoint
`Version`	This is used internally, the version is increased when the projection is edited or reset
`Epoch`	This is used internally, the epoch is increased when the projection is reset

The Status string is a combination of the following values. The first 3 are the most common one, as the other one are transient values while the projection is initialised or stopped

Value	Description
Running	The projection is running and processing events
Stopped	The projection is stopped and is no longer processing new events
Faulted	An error occurred in the projection, `StateReason` will give the fault details, the projection is not processing events
Initial	This is the initial state, before the projection is fully initialised
Suspended	The projection is suspended and will not process events, this happens while stopping the projection
LoadStateRequested	The state of the projection is being retrieved, this happens while the projection is starting
StateLoaded	The state of the projection is loaded, this happens while the projection is starting
Subscribed	The projection has successfully subscribed to its readers, this happens while the projection is starting
FaultedStopping	This happens before the projection is stopped due to an error in the projection
Stopping	The projection is being stopped
CompletingPhase	This happens while the projection is stopping
PhaseCompleted	This happens while the projection is stopping

# Projection management

# Required packages

# Creating a client

# Create a projection

# Restart the subsystem

# Enable a projection

# Disable a projection

# Delete a projection

# Abort a projection

# Reset a projection

# Update a projection

# List all projections

# List continuous projections

# Get Status

# Get state

# Get result

# Projection Details

Projection management

Required packages

Creating a client

Create a projection

Restart the subsystem

Enable a projection

Disable a projection

Delete a projection

Abort a projection

Reset a projection

Update a projection

List all projections

List continuous projections

Get Status

Get state

Get result

Projection Details