Documentation Index

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db.get() Method Documentation

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Method Signature

async db.get(id, callback = null)

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Parameters

1. id (string, required):
   • The unique identifier of the node you want to retrieve.
   • Must be a valid string. If the ID is invalid or not found, the method will return null.
2. callback (function, optional):
   • A function that will be executed when the node is retrieved and whenever its value changes in real-time.
   • If no callback is provided, the method will simply return the node without setting up real-time updates.

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Return Value

• result:
  • The node object corresponding to the provided id.
  • If the node is not found or the id is invalid, this will be null.
• unsubscribe (optional):
  • A function that stops listening for real-time updates.
  • This property is only included if a callback is provided.

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Usage Examples

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1. Retrieve a Node Without Real-Time Updates

const { result } = await db.get('node-id');
console.log(result); // Logs the node object or null if not found

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2. Retrieve a Node With Real-Time Updates

const { result } = await db.get('node-id', (node) => {
  console.log('Node updated:', node);
});

• The callback will be executed immediately with the initial node value.
• It will also be called whenever the node’s value changes in the database.

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3. Stop Listening for Real-Time Updates

const { unsubscribe } = await db.get('node-id', (node) => {
  console.log('Node updated:', node);
});

// Stop listening after some time
setTimeout(() => {
  unsubscribe();
  console.log('Stopped listening for updates.');
}, 5000);

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Error Handling

• If the id is not a valid string, the method logs an error and returns { result: null }.
• If no node is found with the provided id, the method logs an error and returns { result: null }.

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Key Notes

1. Real-Time Updates:
   • Real-time updates are only enabled if a callback is provided.
   • Ensure you call unsubscribe when updates are no longer needed to avoid memory leaks.
2. Asynchronous Nature:
   • The method is asynchronous (async), so always use await or handle it with .then().
3. Data Structure Assumptions:
   • Assumes the underlying data structure (this.graph) is efficient for lookups by id (e.g., a Map).

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Example Use Case

// Fetch and subscribe to updates for a specific node
const { unsubscribe } = await db.get('sensor-123', (node) => {
  console.log(`Sensor value updated: ${node.value}`);
});

// Simulate stopping updates after 10 seconds
setTimeout(() => {
  unsubscribe();
  console.log('Stopped monitoring sensor.');
}, 10000);