Session: How to enable optimistic concurrency?

By default, optimistic concurrency checks are turned off, which means that changes made outside our session object will be overwritten. Checks can be turned on by setting setUseOptimisticConcurrency method from advanced session operations to true and may cause ConcurrencyExceptions to be thrown.

Example I

try (IDocumentSession session = store.openSession()) {
  session.advanced().setUseOptimisticConcurrency(true);

  Product product = new Product();
  product.setName("Some Name");

  session.store(product, "products/999");
  session.saveChanges();

  try (IDocumentSession otherSession = store.openSession()) {
    Product otherProduct = otherSession.load(Product.class, "products/999");
    otherProduct.setName("Other name");

    otherSession.saveChanges();
  }

  product.setName("Better Name");
  session.saveChanges(); // throws ConcurrencyException
}

The above example shows how to enable optimistic concurrency for a particular session. However that can be also turned on globally, that is for all opened sessions by using the convention setDefaultUseOptimisticConcurrency.

Example II

store.getConventions().setDefaultUseOptimisticConcurrency(true);

try (IDocumentSession session = store.openSession()) {
  boolean isSessionUsingOptimisticConcurrency = session.advanced().isUseOptimisticConcurrency(); // will return true
}

Remarks

store.getConventions().setDefaultUseOptimisticConcurrency(true);

try (DocumentSession session = (DocumentSession) store.openSession()) {
  try (CleanCloseable _ = session.getDatabaseCommands().forceReadFromMaster()) {
    // In replicated setup where ONLY reads are load balanced (FailoverBehavior.ReadFromAllServers)
    // and optimistic concurrency checks are turned on
    // you must set 'ForceReadFromMaster' to get the appropriate ETag value for the document
    // when you want to perform document updates (writes)
    // because writes will go to the master server and ETag values between servers are not synchronized

    Product product = session.load(Product.class, "products/999");
    product.setName("New Name");

    session.saveChanges();
  }
}