Event Listener

Event Listener in KtorAdmin

KtorAdmin provides an event listener system that allows you to handle database-related events dynamically. By extending AdminEventListener, you can execute custom logic when inserting, updating, or deleting records in both relational databases (JDBC) and MongoDB.

Understanding AdminEventListener

The AdminEventListener class provides multiple methods to handle different database operations:

Insert Events

• onInsertJdbcData – Called when a new row is inserted into a relational database table.

  • tableName: The name of the table where data is inserted.

  • objectPrimaryKey: The primary key of the inserted object.

  • events: A list of ColumnEvent representing column changes.

• onInsertMongoData – Called when a new document is inserted into a MongoDB collection.

  • collectionName: The name of the collection where data is inserted.

  • objectPrimaryKey: The primary key of the inserted object.

  • events: A list of FieldEvent representing field changes.

Update Events

• onUpdateJdbcData – Called when a row is updated in a relational database table.

  • tableName: The name of the table where data is updated.

  • objectPrimaryKey: The primary key of the updated object.

  • events: A list of ColumnEvent representing column changes.

• onUpdateMongoData – Called when a document is updated in a MongoDB collection.

  • collectionName: The name of the collection where data is updated.

  • objectPrimaryKey: The primary key of the updated object.

  • events: A list of FieldEvent representing field changes.

Delete Events

• onDeleteJdbcObjects – Called when one or more rows are deleted from a relational database table.

  • tableName: The name of the table where data is deleted.

  • objectPrimaryKeys: A list of primary keys of the deleted objects.

• onDeleteMongoObjects – Called when one or more documents are deleted from a MongoDB collection.

  • collectionName: The name of the collection where data is deleted.

  • objectPrimaryKeys: A list of primary keys of the deleted objects.

ColumnEvent and FieldEvent

Whenever an event occurs, you receive a list of ColumnEvent (for relational databases) or FieldEvent (for MongoDB). Each event contains:

• changed – true if the value has changed.

• columnSet / fieldSet – Metadata about the column/field (e.g., name, type).

• value – The new value of the column or field. The type depends on the column definition.

Handling File Uploads in Events

If a column or field is of type file, its value will be an instance of:

FileEvent(
    val fileName: String,
    val bytes: ByteArray
)

You can access fileName and bytes to process the uploaded file. For example, if a row is inserted into the tasks table and contains a video file, you can generate a thumbnail automatically:

class AdminListener() : AdminEventListener() {
    override suspend fun onInsertJdbcData(
        tableName: String,
        objectPrimaryKey: String,
        events: List<ColumnEvent>
    ) {
        if (tableName == "tasks") {
            events.find { it.columnSet.columnName == "file" }?.let {
                if (it.changed.not()) return
                (it.value as? FileEvent)?.also {
                    println("Processing file: ${it.fileName}")
                    // Handle Save Thumbnail
                }
            }
        }
    }
}

Registering the Event Listener

To activate the custom event listener, register it inside the Ktor module:

install(KtorAdmin) {
    registerEventListener(AdminListener())
}

With this setup, you can dynamically process file uploads, log changes, or execute additional logic based on database events.