fix(metrics): addDimensions() documentation and tests (#3964)

Co-authored-by: Andrea Amorosi <dreamorosi@gmail.com>

Author: matteofigus

docs/features/metrics.md

@@ -119,6 +119,18 @@ You can create metrics using the `addMetric` method, and you can create dimensio
     --8<-- "examples/snippets/metrics/customDimensions.ts"
     ```
 
+### Creating dimension sets
+
+You can create separate dimension sets for your metrics using the `addDimensions` method. This allows you to group metrics by different dimension combinations.
+
+When you call `addDimensions()`, it creates a new dimension set rather than adding to the existing dimensions. This is useful when you want to track the same metric across different dimension combinations.
+
+=== "handler.ts"
+
+    ```typescript hl_lines="9 12-15 18-21"
+    --8<-- "examples/snippets/metrics/dimensionSets.ts"
+    ```
+
 !!! tip "Autocomplete Metric Units"
     Use the `MetricUnit` enum to easily find a supported metric unit by CloudWatch. Alternatively, you can pass the value as a string if you already know them e.g. "Count".
 

examples/snippets/metrics/dimensionSets.ts

@@ -0,0 +1,30 @@
+import { MetricUnit, Metrics } from '@aws-lambda-powertools/metrics';
+
+const metrics = new Metrics({
+  namespace: 'serverlessAirline',
+  serviceName: 'orders',
+});
+
+export const handler = async (
+  _event: unknown,
+  _context: unknown
+): Promise<void> => {
+  // Add a single dimension
+  metrics.addDimension('environment', 'prod');
+
+  // Add a new dimension set
+  metrics.addDimensions({
+    dimension1: '1',
+    dimension2: '2',
+  });
+
+  // Add another dimension set
+  metrics.addDimensions({
+    region: 'us-east-1',
+    category: 'books',
+  });
+
+  // Add metrics
+  metrics.addMetric('successfulBooking', MetricUnit.Count, 1);
+  metrics.publishStoredMetrics();
+};

packages/metrics/src/Metrics.ts

@@ -154,6 +154,12 @@ class Metrics extends Utility implements MetricsInterface {
    */
   private dimensions: Dimensions = {};
 
+  /**
+   * Additional dimension sets for the current metrics context
+   * @default []
+   */
+  private dimensionSets: Dimensions[] = [];
+
   /**
    * Service for accessing environment variables
    */
@@ -267,9 +273,35 @@ class Metrics extends Utility implements MetricsInterface {
    * @param dimensions - An object with key-value pairs of dimensions
    */
   public addDimensions(dimensions: Dimensions): void {
-    for (const [name, value] of Object.entries(dimensions)) {
-      this.addDimension(name, value);
+    const newDimensionSet: Dimensions = {};
+    for (const [key, value] of Object.entries(dimensions)) {
+      if (!value) {
+        this.#logger.warn(
+          `The dimension ${key} doesn't meet the requirements and won't be added. Ensure the dimension name and value are non empty strings`
+        );
+        continue;
+      }
+      if (
+        Object.hasOwn(this.dimensions, key) ||
+        Object.hasOwn(this.defaultDimensions, key) ||
+        Object.hasOwn(newDimensionSet, key)
+      ) {
+        this.#logger.warn(
+          `Dimension "${key}" has already been added. The previous value will be overwritten.`
+        );
+      }
+      newDimensionSet[key] = value;
+    }
+
+    const currentCount = this.getCurrentDimensionsCount();
+    const newSetCount = Object.keys(newDimensionSet).length;
+    if (currentCount + newSetCount >= MAX_DIMENSION_COUNT) {
+      throw new RangeError(
+        `The number of metric dimensions must be lower than ${MAX_DIMENSION_COUNT}`
+      );
     }
+
+    this.dimensionSets.push(newDimensionSet);
   }
 
   /**
@@ -447,6 +479,7 @@ class Metrics extends Utility implements MetricsInterface {
    */
   public clearDimensions(): void {
     this.dimensions = {};
+    this.dimensionSets = [];
   }
 
   /**
@@ -692,26 +725,46 @@ class Metrics extends Utility implements MetricsInterface {
       {}
     );
 
-    const dimensionNames = [
-      ...new Set([
+    const dimensionNames = [];
+
+    const allDimensionKeys = new Set([
+      ...Object.keys(this.defaultDimensions),
+      ...Object.keys(this.dimensions),
+    ]);
+
+    if (Object.keys(this.dimensions).length > 0) {
+      dimensionNames.push([...allDimensionKeys]);
+    }
+
+    for (const dimensionSet of this.dimensionSets) {
+      const dimensionSetKeys = new Set([
         ...Object.keys(this.defaultDimensions),
-        ...Object.keys(this.dimensions),
-      ]),
-    ];
+        ...Object.keys(dimensionSet),
+      ]);
+      dimensionNames.push([...dimensionSetKeys]);
+    }
+
+    if (
+      dimensionNames.length === 0 &&
+      Object.keys(this.defaultDimensions).length > 0
+    ) {
+      dimensionNames.push([...Object.keys(this.defaultDimensions)]);
+    }
 
     return {
       _aws: {
         Timestamp: this.#timestamp ?? new Date().getTime(),
         CloudWatchMetrics: [
           {
             Namespace: this.namespace || DEFAULT_NAMESPACE,
-            Dimensions: [dimensionNames],
+            Dimensions: dimensionNames as [string[]],
             Metrics: metricDefinitions,
           },
         ],
       },
       ...this.defaultDimensions,
       ...this.dimensions,
+      ...this.dimensionSets.reduce((acc, dims) => Object.assign(acc, dims), {}),
       ...metricValues,
       ...this.metadata,
     };
@@ -824,9 +877,14 @@ class Metrics extends Utility implements MetricsInterface {
    * Gets the current number of dimensions count.
    */
   private getCurrentDimensionsCount(): number {
+    const dimensionSetsCount = this.dimensionSets.reduce(
+      (total, dimensionSet) => total + Object.keys(dimensionSet).length,
+      0
+    );
     return (
       Object.keys(this.dimensions).length +
-      Object.keys(this.defaultDimensions).length
+      Object.keys(this.defaultDimensions).length +
+      dimensionSetsCount
     );
   }