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Session: How to Subscribe to Events

The concept of events provides users with a mechanism to perform custom actions in response to operations taken in a session.

The listener is invoked when a particular action is executed on an entity or querying is performed.

Subscribing to an event

Subscribing an event can be done in the DocumentStore object, which will be valid for all future sessions or subscribing in an already opened session with session.advanced which will overwrite the existing event for the current session.

"beforeStore" event

This event is invoked as a part of saveChanges(), but before it is actually sent to the server.

The callback passes the argument BeforeStoreEventArgs that consists of the Session entity's ID and the entity itself.

Example

Say we want to discontinue all of the products that are not in stock. After we add a listener to the event, it's going to emit on every stored entity.

// subscribe to the event
store.on("beforeStore", (args) => {
    if (args.entity instanceof Product) {
        const product = args.entity;
        if (product.unitsInStock === 0) {
            product.discontinued = true;
        }
    }
});

{
    const session = store.openSession();
    const product1 = new Product();
    product1.name = "RavenDB v3.5";
    product1.unitsInStock = 0;

    await session.store(product1);

    const product2 = new Product();
    product2.name = "RavenDB v4.0";
    product2.unitsInStock = 1000;
    await session.store(product2);

    await session.saveChanges();  // Here's where the event is emitted
}

"beforeDelete" event

This event is invoked as a part of saveChanges(), but before it actually sends the deleted entities to the server.

It takes the argument BeforeDeleteEventArgs, that consists of the Session entity's ID and the entity itself.

Example

To prevent anyone from deleting entities we can create a listener as follows:

// subscribe to the event
store.on("beforeDelete", args => {
    throw new Error("Not implemented");
});

// open a session and delete entity
{
    const session = store.openSession();
    const product = await session.load("products/1-A");

    session.delete(product);

    await session.saveChanges(); // "Not implemented" error will be thrown here
}

"afterSaveChanges" event

This event is invoked after the saveChanges() is returned. It takes the argument AfterSaveChangesEventArgs that consists of the Session entity's ID and the entity itself with the updated metadata from the server.

Example

If we want to log each entity that was saved, we can create a method as follows:

store.on("afterSaveChanges", args => {
    log("Document " + args.documentId + " was saved.");
});

"beforeQuery" event

This event is invoked just before the query is sent to the server.

It takes the argument BeforeQueryEventArgs, that consists of the Session and the IDocumentQueryCustomization.

Example I

If you want to disable caching of all query results, you can implement the method as follows:

store.on("beforeQuery", args => {
    args.queryCustomization.noCaching();
});

Example II

If you want each query to wait for non-stale results you can create an event as follows:

store.on("beforeQuery", args => {
    args.queryCustomization
        .waitForNonStaleResults(30000);
});