add length()

Author: cherylEnkidu

Firestore/Swift/Source/ExpressionImplementation.swift

@@ -460,6 +460,10 @@ public extension Expression {
 
   // --- Added String Operations ---
 
+  func length() -> FunctionExpression {
+    return FunctionExpression("length", [self])
+  }
+
   func charLength() -> FunctionExpression {
     return FunctionExpression("char_length", [self])
   }

Firestore/Swift/Source/SwiftAPI/Pipeline/Expressions/Expression.swift

@@ -650,6 +650,16 @@ public protocol Expression: Sendable {
 
   // MARK: String Operations
 
+  /// Creates an expression that returns the length of a string.
+  ///
+  /// ```swift
+  /// // Get the length of the "name" field.
+  /// Field("name").length()
+  /// ```
+  ///
+  /// - Returns: A new `FunctionExpression` representing the length of the string.
+  func length() -> FunctionExpression
+
   /// Creates an expression that calculates the character length of a string in UTF-8.
   /// Assumes `self` evaluates to a string.
   ///

Firestore/Swift/Tests/Integration/PipelineTests.swift

@@ -1918,6 +1918,32 @@ class PipelineIntegrationTests: FSTIntegrationTestCase {
     TestHelper.compare(pipelineSnapshot: snapshot, expected: expectedResults, enforceOrder: true)
   }
 
+  func testLength() async throws {
+    let collRef = collectionRef(withDocuments: [
+      "doc1": ["value": "abc"],
+      "doc2": ["value": ""],
+      "doc3": ["value": "a"],
+    ])
+    let db = collRef.firestore
+
+    let pipeline = db.pipeline()
+      .collection(collRef.path)
+      .select([
+        Field("value").length().as("lengthValue"),
+      ])
+      .sort([Field("lengthValue").ascending()])
+
+    let snapshot = try await pipeline.execute()
+
+    let expectedResults: [[String: Sendable]] = [
+      ["lengthValue": 0],
+      ["lengthValue": 1],
+      ["lengthValue": 3],
+    ]
+
+    TestHelper.compare(pipelineSnapshot: snapshot, expected: expectedResults, enforceOrder: true)
+  }
+
   func testLike() async throws {
     let collRef = collectionRef(withDocuments: bookDocs)
     let db = collRef.firestore