[Kotlin] Independent Having Clauses

Author: jeffgbutler

src/main/kotlin/org/mybatis/dynamic/sql/util/kotlin/KotlinSelectBuilder.kt

@@ -52,8 +52,8 @@ class KotlinSelectBuilder(private val fromGatherer: QueryExpressionDSL.FromGathe
     }
 
     fun having(criteria: GroupingCriteriaReceiver): Unit =
-        with(GroupingCriteriaCollector().apply(criteria)) {
-            this@KotlinSelectBuilder.getDsl().applyHaving(initialCriterion, subCriteria)
+        GroupingCriteriaCollector().apply(criteria).let {
+            getDsl().applyHaving(it.initialCriterion, it.subCriteria)
         }
 
     fun orderBy(vararg columns: SortSpecification) {

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

@@ -93,6 +93,24 @@ import org.mybatis.dynamic.sql.where.condition.IsNull
  */
 fun where(receiver: GroupingCriteriaReceiver): GroupingCriteriaReceiver = receiver
 
+/**
+ * Simple function for code beautification. This allows creation of an independent having clause
+ * that can be reused in different statements. For example:
+ *
+ * val havingClause = where { count() isGreaterThanTo 1 }
+ *
+ * val rows = select(id, count()) {
+ *   from(foo)
+ *   groupBy(id)
+ *   having(havingClause)
+ * }
+ *
+ * Use of this function is optional. You can also write code like this:
+ *
+ * val havingClause: GroupingCriteriaReceiver = { count() isGreaterThanTo 1 }
+ */
+fun having(receiver: GroupingCriteriaReceiver): GroupingCriteriaReceiver = receiver
+
 // support for criteria without initial conditions
 fun and(receiver: GroupingCriteriaReceiver): AndOrCriteriaGroup =
     with(GroupingCriteriaCollector().apply(receiver)) {

src/test/kotlin/examples/kotlin/mybatis3/general/KGroupingTest.kt

@@ -27,6 +27,7 @@ import org.mybatis.dynamic.sql.exception.InvalidSqlException
 import org.mybatis.dynamic.sql.util.kotlin.elements.add
 import org.mybatis.dynamic.sql.util.kotlin.elements.column
 import org.mybatis.dynamic.sql.util.kotlin.elements.count
+import org.mybatis.dynamic.sql.util.kotlin.elements.having
 import org.mybatis.dynamic.sql.util.kotlin.elements.isBetween
 import org.mybatis.dynamic.sql.util.kotlin.elements.isLessThanOrEqualTo
 import org.mybatis.dynamic.sql.util.kotlin.mybatis3.select
@@ -360,6 +361,25 @@ class KGroupingTest {
         assertThat(selectStatement.parameters).containsEntry("p1", 6L)
     }
 
+    @Test
+    fun testIndependentHaving() {
+        val havingClause = having { count() isGreaterThan 6 }
+
+        val selectStatement = select(A, count()) {
+            from(foo)
+            groupBy(A)
+            having(havingClause)
+        }
+
+        val expected = "select A, count(*)" +
+                " from Foo" +
+                " group by A" +
+                " having count(*) > #{parameters.p1}"
+
+        assertThat(selectStatement.selectStatement).isEqualTo(expected)
+        assertThat(selectStatement.parameters).containsEntry("p1", 6L)
+    }
+
     @Test
     fun testHavingMultipleConditions() {
         val selectStatement = select(A, count()) {