[SPARK-52149] Add String.toExpression extension

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

This PR aims to introduce `String.toExpression` extension to simplify the code.

### Why are the changes needed?

To simplify the code by reducing the repetition.

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

No.

### How was this patch tested?

Pass the CIs.

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

No.

Closes #148 from dongjoon-hyun/SPARK-52149.

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

Author: dongjoon-hyun

Sources/SparkConnect/DataFrameWriterV2.swift

@@ -72,11 +72,7 @@ public actor DataFrameWriterV2: Sendable {
   /// - Parameter columns: Columns to partition
   /// - Returns: A ``DataFrameWriterV2``.
   public func partitionBy(_ columns: String...) -> DataFrameWriterV2 {
-    self.partitioningColumns = columns.map {
-      var expr = Spark_Connect_Expression()
-      expr.expressionString = $0.toExpressionString
-      return expr
-    }
+    self.partitioningColumns = columns.map { $0.toExpression }
     return self
   }
 

Sources/SparkConnect/Extension.swift

@@ -126,6 +126,14 @@ extension String {
     return expression
   }
 
+  var toExpression: Spark_Connect_Expression {
+    var expressionString = ExpressionString()
+    expressionString.expression = self
+    var expression = Spark_Connect_Expression()
+    expression.expressionString = expressionString
+    return expression
+  }
+
   var toExplainMode: ExplainMode {
     let mode = switch self {
     case "codegen": ExplainMode.codegen

Sources/SparkConnect/GroupedData.swift

@@ -32,16 +32,8 @@ public actor GroupedData {
     var aggregate = Aggregate()
     aggregate.input = await (self.df.getPlan() as! Plan).root
     aggregate.groupType = self.groupType
-    aggregate.groupingExpressions = self.groupingCols.map {
-      var expr = Spark_Connect_Expression()
-      expr.expressionString = $0.toExpressionString
-      return expr
-    }
-    aggregate.aggregateExpressions = exprs.map {
-      var expr = Spark_Connect_Expression()
-      expr.expressionString = $0.toExpressionString
-      return expr
-    }
+    aggregate.groupingExpressions = self.groupingCols.map { $0.toExpression }
+    aggregate.aggregateExpressions = exprs.map { $0.toExpression }
     var relation = Relation()
     relation.aggregate = aggregate
     var plan = Plan()

Sources/SparkConnect/SparkConnectClient.swift

@@ -508,11 +508,7 @@ public actor SparkConnectClient {
   static func getProjectExprs(_ child: Relation, _ exprs: [String]) -> Plan {
     var project = Project()
     project.input = child
-    let expressions: [Spark_Connect_Expression] = exprs.map {
-      var expression = Spark_Connect_Expression()
-      expression.exprType = .expressionString($0.toExpressionString)
-      return expression
-    }
+    let expressions: [Spark_Connect_Expression] = exprs.map { $0.toExpression }
     project.expressions = expressions
     var relation = Relation()
     relation.project = project
@@ -908,11 +904,7 @@ public actor SparkConnectClient {
   ) -> Plan {
     var repartitionByExpression = RepartitionByExpression()
     repartitionByExpression.input = child
-    repartitionByExpression.partitionExprs = partitionExprs.map {
-      var expr = Spark_Connect_Expression()
-      expr.expressionString = $0.toExpressionString
-      return expr
-    }
+    repartitionByExpression.partitionExprs = partitionExprs.map { $0.toExpression }
     if let numPartitions {
       repartitionByExpression.numPartitions = numPartitions
     }
@@ -932,18 +924,10 @@ public actor SparkConnectClient {
   ) -> Plan {
     var unpivot = Spark_Connect_Unpivot()
     unpivot.input = child
-    unpivot.ids = ids.map {
-      var expr = Spark_Connect_Expression()
-      expr.expressionString = $0.toExpressionString
-      return expr
-    }
+    unpivot.ids = ids.map { $0.toExpression }
     if let values {
       var unpivotValues = Spark_Connect_Unpivot.Values()
-      unpivotValues.values = values.map {
-        var expr = Spark_Connect_Expression()
-        expr.expressionString = $0.toExpressionString
-        return expr
-      }
+      unpivotValues.values = values.map { $0.toExpression }
       unpivot.values = unpivotValues
     }
     unpivot.variableColumnName = variableColumnName
@@ -958,11 +942,7 @@ public actor SparkConnectClient {
   static func getTranspose(_ child: Relation, _ indexColumn: [String]) -> Plan {
     var transpose = Spark_Connect_Transpose()
     transpose.input = child
-    transpose.indexColumns = indexColumn.map {
-      var expr = Spark_Connect_Expression()
-      expr.expressionString = $0.toExpressionString
-      return expr
-    }
+    transpose.indexColumns = indexColumn.map { $0.toExpression }
     var relation = Relation()
     relation.transpose = transpose
     var plan = Plan()