More idiomatic DSL for Kotlin casts

Author: jeffgbutler

src/main/kotlin/org/mybatis/dynamic/sql/util/kotlin/elements/CastDSL.kt

@@ -0,0 +1,37 @@
+/*
+ *    Copyright 2016-2024 the original author or authors.
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *       https://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+package org.mybatis.dynamic.sql.util.kotlin.elements
+
+import org.mybatis.dynamic.sql.BasicColumn
+import org.mybatis.dynamic.sql.SqlBuilder
+import org.mybatis.dynamic.sql.select.function.Cast
+import org.mybatis.dynamic.sql.util.kotlin.assertNull
+
+class CastDSL {
+    internal var cast: Cast? = null
+        private set(value) {
+            assertNull(field, "ERROR.43") //$NON-NLS-1$
+            field = value
+        }
+
+    infix fun String.`as`(targetType: String) {
+        cast = SqlBuilder.cast(this).`as`(targetType)
+    }
+
+    infix fun BasicColumn.`as`(targetType: String) {
+        cast = SqlBuilder.cast(this).`as`(targetType)
+    }
+}

src/main/kotlin/org/mybatis/dynamic/sql/util/kotlin/elements/SqlElements.kt

@@ -23,7 +23,6 @@ import org.mybatis.dynamic.sql.BoundValue
 import org.mybatis.dynamic.sql.Constant
 import org.mybatis.dynamic.sql.SortSpecification
 import org.mybatis.dynamic.sql.SqlBuilder
-import org.mybatis.dynamic.sql.SqlBuilder.CastFinisher
 import org.mybatis.dynamic.sql.SqlColumn
 import org.mybatis.dynamic.sql.StringConstant
 import org.mybatis.dynamic.sql.VisitableCondition
@@ -50,6 +49,7 @@ import org.mybatis.dynamic.sql.select.function.Upper
 import org.mybatis.dynamic.sql.util.kotlin.GroupingCriteriaCollector
 import org.mybatis.dynamic.sql.util.kotlin.GroupingCriteriaReceiver
 import org.mybatis.dynamic.sql.util.kotlin.KotlinSubQueryBuilder
+import org.mybatis.dynamic.sql.util.kotlin.invalidIfNull
 import org.mybatis.dynamic.sql.where.condition.IsBetween
 import org.mybatis.dynamic.sql.where.condition.IsEqualTo
 import org.mybatis.dynamic.sql.where.condition.IsEqualToColumn
@@ -167,11 +167,8 @@ fun <T> subtract(
     vararg subsequentColumns: BasicColumn
 ): Subtract<T> = Subtract.of(firstColumn, secondColumn, subsequentColumns.asList())
 
-fun cast(value: String): CastFinisher = SqlBuilder.cast(value)
-
-fun cast(column: BasicColumn): CastFinisher = SqlBuilder.cast(column)
-
-infix fun CastFinisher.`as`(targetType: String): Cast = this.`as`(targetType)
+fun cast(receiver: CastDSL.() -> Unit): Cast =
+    invalidIfNull(CastDSL().apply(receiver).cast, "ERROR.43")
 
 fun <T> concat(
     firstColumn: BindableColumn<T>,

src/main/resources/org/mybatis/dynamic/sql/util/messages.properties

@@ -59,4 +59,5 @@ ERROR.39=When clauses in case expressions must render (optional conditions are n
 ERROR.40=Case expressions must have at least one "when" clause
 ERROR.41=You cannot call "then" in a Kotlin case expression more than once
 ERROR.42=You cannot call `else` in a Kotlin case expression more than once
+ERROR.43=A Kotlin cast expression must have one, and only one, cast 
 INTERNAL.ERROR=Internal Error {0}

src/test/kotlin/examples/kotlin/animal/data/KCaseExpressionTest.kt

@@ -28,7 +28,6 @@ import org.junit.jupiter.api.Test
 import org.mybatis.dynamic.sql.exception.InvalidSqlException
 import org.mybatis.dynamic.sql.util.Messages
 import org.mybatis.dynamic.sql.util.kotlin.KInvalidSQLException
-import org.mybatis.dynamic.sql.util.kotlin.elements.`as`
 import org.mybatis.dynamic.sql.util.kotlin.elements.case
 import org.mybatis.dynamic.sql.util.kotlin.elements.cast
 import org.mybatis.dynamic.sql.util.kotlin.elements.isEqualTo
@@ -217,7 +216,7 @@ class KCaseExpressionTest {
                         or { animalName isEqualTo "Big brown bat" }
                         then(value("Bat"))
                     }
-                    `else`(cast(value("Not a Fox or a bat")) `as` "VARCHAR(30)")
+                    `else`(cast { value("Not a Fox or a bat") `as` "VARCHAR(30)" })
                 }.`as`("AnimalType")
             ) {
                 from(animalData, "a")
@@ -720,7 +719,7 @@ class KCaseExpressionTest {
             val selectStatement = select(
                 animalName,
                 case(animalName) {
-                    `when`(isEqualTo("Artic fox"), isEqualTo("Red fox")) { then(cast("It's a fox") `as` "VARCHAR(30)") }
+                    `when`(isEqualTo("Artic fox"), isEqualTo("Red fox")) { then(cast { "It's a fox" `as` "VARCHAR(30)" })}
                     `else`("It's not a fox")
                 }.`as`("IsAFox")
             ) {