add join()

Author: cherylEnkidu

Firestore/Swift/Source/ExpressionImplementation.swift

@@ -609,6 +609,10 @@ public extension Expression {
 
   // --- Added String Operations ---
 
+  func join(delimiter: String) -> FunctionExpression {
+    return FunctionExpression("join", [self, Constant(delimiter)])
+  }
+
   func length() -> FunctionExpression {
     return FunctionExpression("length", [self])
   }

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

@@ -706,6 +706,19 @@ public protocol Expression: Sendable {
 
   // MARK: String Operations
 
+  /// Creates an expression that joins the elements of an array of strings with a given separator.
+  ///
+  /// Assumes `self` evaluates to an array of strings.
+  ///
+  /// ```swift
+  /// // Join the "tags" array with a ", " separator.
+  /// Field("tags").join(separator: ", ")
+  /// ```
+  ///
+  /// - Parameter delimiter: The string to use as a delimiter.
+  /// - Returns: A new `FunctionExpression` representing the joined string.
+  func join(delimiter: String) -> FunctionExpression
+
   /// Creates an expression that returns the length of a string.
   ///
   /// ```swift

Firestore/Swift/Tests/Integration/PipelineTests.swift

@@ -2878,6 +2878,31 @@ class PipelineIntegrationTests: FSTIntegrationTestCase {
     TestHelper.compare(snapshot: snapshot, expected: expectedResults, enforceOrder: true)
   }
 
+  func testJoinWorks() async throws {
+    let collRef = collectionRef(withDocuments: [
+      "doc1": ["tags": ["a", "b", "c"]],
+      "doc2": ["tags": ["d", "e"]],
+      "doc3": ["tags": []],
+    ])
+    let db = collRef.firestore
+
+    let pipeline = db.pipeline()
+      .collection(collRef.path)
+      .select([
+        Field("tags").join(delimiter: ", ").as("tagsString"),
+      ])
+
+    let snapshot = try await pipeline.execute()
+
+    let expectedResults: [[String: Sendable]] = [
+      ["tagsString": "a, b, c"],
+      ["tagsString": "d, e"],
+      ["tagsString": ""],
+    ]
+
+    TestHelper.compare(snapshot: snapshot, expected: expectedResults, enforceOrder: false)
+  }
+
   func testSupportsRand() async throws {
     let collRef = collectionRef(withDocuments: bookDocs)
     let db = collRef.firestore

Firestore/Swift/Tests/TestHelper/TestHelper.swift

@@ -161,7 +161,7 @@ public enum TestHelper {
 
     for (key, value1) in dict1 {
       guard let value2 = dict2[key], areEqual(value1, value2) else {
-        XCTFail("""
+        print("""
         Dictionary value mismatch for key: '\(key)'
         Actual value: '\(String(describing: value1))' (from dict1)
         Expected value:   '\(String(describing: dict2[key]))' (from dict2)
@@ -180,7 +180,7 @@ public enum TestHelper {
     for (index, value1) in array1.enumerated() {
       let value2 = array2[index]
       if !areEqual(value1, value2) {
-        XCTFail("""
+        print("""
         Array value mismatch.
         Actual array value: '\(String(describing: value1))'
         Expected array value:   '\(String(describing: value2))'