[SPARK-51702] Revise sparkSession/read/write/columns/schema/dtypes/storageLevel API

### What changes were proposed in this pull request?

This PR aims to revise `sparkSession/read/write/columns/schema/dtypes/storageLevel` API to resemble the other language clients' APIs.

### Why are the changes needed?

To provide a consistent UX to the users.

### Does this PR introduce _any_ user-facing change?

- Change `func` to `var` like the following.
```swift
- public func schema() async throws -> String {
+ public var schema: String {
+   get async throws {
```

- Add `public` explicitly.
- Revise test cases accordingly.

### How was this patch tested?

Pass the CIs and manual review.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #39 from dongjoon-hyun/SPARK-51702.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

Sources/SparkConnect/DataFrame.swift

@@ -29,7 +29,7 @@ import Synchronization
 public actor DataFrame: Sendable {
   var spark: SparkSession
   var plan: Plan
-  var schema: DataType? = nil
+  private var _schema: DataType? = nil
   private var batches: [RecordBatch] = [RecordBatch]()
 
   /// Create a new `DataFrame`instance with the given Spark session and plan.
@@ -57,7 +57,7 @@ public actor DataFrame: Sendable {
   /// Set the schema. This is used to store the analized schema response from `Spark Connect` server.
   /// - Parameter schema: <#schema description#>
   private func setSchema(_ schema: DataType) {
-    self.schema = schema
+    self._schema = schema
   }
 
   /// Add `Apache Arrow`'s `RecordBatch`s to the internal array.
@@ -67,9 +67,10 @@ public actor DataFrame: Sendable {
   }
 
   /// Return the `SparkSession` of this `DataFrame`.
-  /// - Returns: A `SparkSession`
-  public func sparkSession() -> SparkSession {
-    return self.spark
+  public var sparkSession: SparkSession {
+    get async throws {
+      return self.spark
+    }
   }
 
   /// A method to access the underlying Spark's `RDD`.
@@ -82,32 +83,35 @@ public actor DataFrame: Sendable {
   }
 
   /// Return an array of column name strings
-  /// - Returns: a string array
-  public func columns() async throws -> [String] {
-    var columns: [String] = []
-    try await analyzePlanIfNeeded()
-    for field in self.schema!.struct.fields {
-      columns.append(field.name)
+  public var columns: [String] {
+    get async throws {
+      var columns: [String] = []
+      try await analyzePlanIfNeeded()
+      for field in self._schema!.struct.fields {
+        columns.append(field.name)
+      }
+      return columns
     }
-    return columns
   }
 
   /// Return a `JSON` string of data type because we cannot expose the internal type ``DataType``.
-  /// - Returns: a `JSON` string.
-  public func schema() async throws -> String {
-    try await analyzePlanIfNeeded()
-    return try self.schema!.jsonString()
+  public var schema: String {
+    get async throws {
+      try await analyzePlanIfNeeded()
+      return try self._schema!.jsonString()
+    }
   }
 
-  var dtypes: [(String, String)] {
+  /// Returns all column names and their data types as an array.
+  public var dtypes: [(String, String)] {
     get async throws {
       try await analyzePlanIfNeeded()
-      return try self.schema!.struct.fields.map { ($0.name, try $0.dataType.simpleString) }
+      return try self._schema!.struct.fields.map { ($0.name, try $0.dataType.simpleString) }
     }
   }
 
   private func analyzePlanIfNeeded() async throws {
-    if self.schema != nil {
+    if self._schema != nil {
       return
     }
     try await withGRPCClient(
@@ -224,7 +228,7 @@ public actor DataFrame: Sendable {
   public func show() async throws {
     try await execute()
 
-    if let schema = self.schema {
+    if let schema = self._schema {
       var columns: [TextTableColumn] = []
       for f in schema.struct.fields {
         columns.append(TextTableColumn(header: f.name))
@@ -342,7 +346,7 @@ public actor DataFrame: Sendable {
     return self
   }
 
-  var storageLevel: StorageLevel {
+  public var storageLevel: StorageLevel {
     get async throws {
       try await withGRPCClient(
         transport: .http2NIOPosix(
@@ -403,7 +407,7 @@ public actor DataFrame: Sendable {
   }
 
   /// Returns a ``DataFrameWriter`` that can be used to write non-streaming data.
-  var write: DataFrameWriter {
+  public var write: DataFrameWriter {
     get {
       return DataFrameWriter(df: self)
     }

Sources/SparkConnect/SparkSession.swift

@@ -75,7 +75,7 @@ public actor SparkSession {
   var serverSideSessionID: String = ""
 
   /// A variable for ``SparkContext``. This is designed to throw exceptions by Apache Spark.
-  var sparkContext: SparkContext {
+  public var sparkContext: SparkContext {
     get throws {
       // SQLSTATE: 0A000
       // [UNSUPPORTED_CONNECT_FEATURE.SESSION_SPARK_CONTEXT]
@@ -119,7 +119,7 @@ public actor SparkSession {
 
   /// Returns a ``DataFrameReader`` that can be used to read non-streaming data in as a
   /// `DataFrame`
-  var read: DataFrameReader {
+  public var read: DataFrameReader {
     get {
       return DataFrameReader(sparkSession: self)
     }
@@ -140,7 +140,7 @@ public actor SparkSession {
   /// This is defined as the return type of `SparkSession.sparkContext` method.
   /// This is an empty `Struct` type because `sparkContext` method is designed to throw
   /// `UNSUPPORTED_CONNECT_FEATURE.SESSION_SPARK_CONTEXT`.
-  struct SparkContext {
+  public struct SparkContext: Sendable {
   }
 
   /// A builder to create ``SparkSession``

Tests/SparkConnectTests/DataFrameTests.swift

@@ -26,7 +26,7 @@ struct DataFrameTests {
   @Test
   func sparkSession() async throws {
     let spark = try await SparkSession.builder.getOrCreate()
-    #expect(try await spark.range(1).sparkSession() == spark)
+    #expect(try await spark.range(1).sparkSession == spark)
     await spark.stop()
   }
 
@@ -42,30 +42,30 @@ struct DataFrameTests {
   @Test
   func columns() async throws {
     let spark = try await SparkSession.builder.getOrCreate()
-    #expect(try await spark.sql("SELECT 1 as col1").columns() == ["col1"])
-    #expect(try await spark.sql("SELECT 1 as col1, 2 as col2").columns() == ["col1", "col2"])
-    #expect(try await spark.sql("SELECT CAST(null as STRING) col1").columns() == ["col1"])
-    #expect(try await spark.sql("DROP TABLE IF EXISTS nonexistent").columns() == [])
+    #expect(try await spark.sql("SELECT 1 as col1").columns == ["col1"])
+    #expect(try await spark.sql("SELECT 1 as col1, 2 as col2").columns == ["col1", "col2"])
+    #expect(try await spark.sql("SELECT CAST(null as STRING) col1").columns == ["col1"])
+    #expect(try await spark.sql("DROP TABLE IF EXISTS nonexistent").columns == [])
     await spark.stop()
   }
 
   @Test
   func schema() async throws {
     let spark = try await SparkSession.builder.getOrCreate()
 
-    let schema1 = try await spark.sql("SELECT 'a' as col1").schema()
+    let schema1 = try await spark.sql("SELECT 'a' as col1").schema
     #expect(
       schema1
         == #"{"struct":{"fields":[{"name":"col1","dataType":{"string":{"collation":"UTF8_BINARY"}}}]}}"#
     )
 
-    let schema2 = try await spark.sql("SELECT 'a' as col1, 'b' as col2").schema()
+    let schema2 = try await spark.sql("SELECT 'a' as col1, 'b' as col2").schema
     #expect(
       schema2
         == #"{"struct":{"fields":[{"name":"col1","dataType":{"string":{"collation":"UTF8_BINARY"}}},{"name":"col2","dataType":{"string":{"collation":"UTF8_BINARY"}}}]}}"#
     )
 
-    let emptySchema = try await spark.sql("DROP TABLE IF EXISTS nonexistent").schema()
+    let emptySchema = try await spark.sql("DROP TABLE IF EXISTS nonexistent").schema
     #expect(emptySchema == #"{"struct":{}}"#)
     await spark.stop()
   }
@@ -136,15 +136,15 @@ struct DataFrameTests {
   @Test
   func selectNone() async throws {
     let spark = try await SparkSession.builder.getOrCreate()
-    let emptySchema = try await spark.range(1).select().schema()
+    let emptySchema = try await spark.range(1).select().schema
     #expect(emptySchema == #"{"struct":{}}"#)
     await spark.stop()
   }
 
   @Test
   func select() async throws {
     let spark = try await SparkSession.builder.getOrCreate()
-    let schema = try await spark.range(1).select("id").schema()
+    let schema = try await spark.range(1).select("id").schema
     #expect(
       schema
         == #"{"struct":{"fields":[{"name":"id","dataType":{"long":{}}}]}}"#
@@ -155,7 +155,7 @@ struct DataFrameTests {
   @Test
   func selectMultipleColumns() async throws {
     let spark = try await SparkSession.builder.getOrCreate()
-    let schema = try await spark.sql("SELECT * FROM VALUES (1, 2)").select("col2", "col1").schema()
+    let schema = try await spark.sql("SELECT * FROM VALUES (1, 2)").select("col2", "col1").schema
     #expect(
       schema
         == #"{"struct":{"fields":[{"name":"col2","dataType":{"integer":{}}},{"name":"col1","dataType":{"integer":{}}}]}}"#
@@ -167,7 +167,7 @@ struct DataFrameTests {
   func selectInvalidColumn() async throws {
     let spark = try await SparkSession.builder.getOrCreate()
     try await #require(throws: Error.self) {
-      let _ = try await spark.range(1).select("invalid").schema()
+      let _ = try await spark.range(1).select("invalid").schema
     }
     await spark.stop()
   }