![npm serverless event store npm serverless event store](https://d2908q01vomqb2.cloudfront.net/1b6453892473a467d07372d45eb05abc2031647a/2020/06/12/ask-3-b-1024x475.png)
This value is used by the next event as it's previousId value to guard against a Lost Event problem. Cannot be null but can be an empty string. Part of a composite foreign key to entity_events.
![npm serverless event store npm serverless event store](https://miro.medium.com/max/1094/1*_GP4Em4b7BscsQrVa7IfjQ.png)
The entity_events table controls the entity and event names that can be used in the events table itself therough the use of composite foreign keys. It must be populated before events can be appended to the main table called events.
![npm serverless event store npm serverless event store](https://miro.medium.com/max/1400/1*vO9zg0LTp6uhh20JpmYG9A.png)
The first, entity_events, contains the event definitions for an entity type. This event store consists of two tables as described in the DDL. Event and entity names must be defined before use. A client cannot insert an event from the wrong entity. Entity and Event Validation Event and Entity names cannot be mispelled or misapplied.Event race conditions are Impossible The event store prevents a client from writing an event to an entity if another event has been inserted after the client has replayed an event stream.Insertion-Ordered Events must be consistently replayable in the order they were inserted.Append-Only Once events are created, they cannot be deleted, updated or otherwise modified.This expression of previous event ID enables SQL Event Store to guarantee that events are written sequentially, without losing any concurrent appends of other events in for the same entity.Īppends to other entities do not affect each other, so many events can be appended to many events concurrently without suffering serialization penalties that “single writer” systems can cause.
![npm serverless event store npm serverless event store](https://twilio-cms-prod.s3.amazonaws.com/original_images/AWS-Lambda-Node-js-Twilio-SMS_GPNFnKv.png)
In this event store, each event has a reference to the previous event, much like a backward-linked list. Events can create new entities, and in that first event, the entity key is presented as the identifying key for newly-created entity.Įvents follow other events in a sequence. In this event store, an event cannot exist without an entity to apply it to. Entities are individually identified by business-relevant keys that uniquely identify one entity from another. It has a name, like food-eaten, and it is scoped to an Entity, or an identifiable existence in the world. Conceptual ModelĪn Event is an unalterable statement of fact that has occurred in the past. The test will dump the test database to test-event-store.sqlite for your examination. The test uses sql.js, the pure Javascript port of SQLite for reliable compilation and test execution. One must have Node and NPM installed (Node 10 is what I used) and then: It will connect to the postgres server defined in the environment variables, according to node-postgres. The postgres version can be tested with the test-postgres.js script. It was built and tested on Postgres 11 but can be ported to earlier versions as needed. The Postgres version of SQL event store has the same behavior as the SQLite version. The project includes a Postgres version of the DDL. This event store can also be ported to most SQL RDBMS and accessed from any number of writers, including high-load serverless functions, without a coordinating “single writer” process. This SQLite event store can be used in highly-constrained environments that require an embedded event store, like a mobile device or an IoT system. This project uses a node test suite and SQLite to ensure the DDL complies with the design requirements. You are assumed to have familiarity with event sourcing. The database rules are intended to prevent incorrect information from entering into an event stream. Demonstration of a SQL event store with deduplication and guaranteed event ordering.