Add support for selectDistinct in union queries

Author: jeffgbutler

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

@@ -22,21 +22,27 @@ import org.mybatis.dynamic.sql.select.SelectModel
 
 class KotlinUnionBuilder(private val dsl: QueryExpressionDSL<SelectModel>) {
     fun select(vararg selectList: BasicColumn) =
-        select(listOf(*selectList))
+        select(selectList.toList())
 
     fun select(selectList: List<BasicColumn>) =
-        KotlinUnionFromGatherer(dsl, selectList)
+        KotlinUnionFromGatherer(dsl, dsl.union().select(selectList))
+
+    fun selectDistinct(vararg selectList: BasicColumn) =
+        selectDistinct(selectList.toList())
+
+    fun selectDistinct(selectList: List<BasicColumn>) =
+        KotlinUnionFromGatherer(dsl, dsl.union().selectDistinct(selectList))
 }
 
 class KotlinUnionFromGatherer(
     private val dsl: QueryExpressionDSL<SelectModel>,
-    private val selectList: List<BasicColumn>
+    private val fromGatherer: QueryExpressionDSL.FromGatherer<SelectModel>
 ) {
     fun from(
         table: SqlTable,
         enhance: KotlinUnionQueryBuilder.() -> KotlinUnionQueryBuilder
     ): QueryExpressionDSL<SelectModel> {
-        val unionBuilder = KotlinUnionQueryBuilder(dsl.union().select(selectList).from(table))
+        val unionBuilder = KotlinUnionQueryBuilder(fromGatherer.from(table))
         enhance(unionBuilder)
         return dsl
     }
@@ -46,7 +52,7 @@ class KotlinUnionFromGatherer(
         alias: String,
         enhance: KotlinUnionQueryBuilder.() -> KotlinUnionQueryBuilder
     ): QueryExpressionDSL<SelectModel> {
-        val unionBuilder = KotlinUnionQueryBuilder(dsl.union().select(selectList).from(table, alias))
+        val unionBuilder = KotlinUnionQueryBuilder(fromGatherer.from(table, alias))
         enhance(unionBuilder)
         return dsl
     }

src/test/kotlin/examples/kotlin/spring/canonical/CanonicalSpringKotlinTest.kt

@@ -506,6 +506,79 @@ class CanonicalSpringKotlinTest {
         }
     }
 
+    @Test
+    fun testRawSelectWithUnionAndDistinct() {
+        val selectStatement = select(
+            id.`as`("A_ID"), firstName, lastName, birthDate, employed, occupation,
+            addressId
+        ).from(Person) {
+            where(id, isEqualTo(1))
+            union {
+                select(
+                    id.`as`("A_ID"), firstName, lastName, birthDate, employed, occupation,
+                    addressId
+                ).from(Person) {
+                    where(id, isEqualTo(2))
+                }
+            }
+            union {
+                selectDistinct(
+                    id.`as`("A_ID"), firstName, lastName, birthDate, employed, occupation,
+                    addressId
+                ).from(Person, "p") {
+                    where(id, isEqualTo(3))
+                }
+            }
+        }
+
+        val expected = "select id as A_ID, first_name, last_name, birth_date, employed, occupation, address_id " +
+                "from Person " +
+                "where id = :p1 " +
+                "union " +
+                "select id as A_ID, first_name, last_name, birth_date, employed, occupation, address_id " +
+                "from Person " +
+                "where id = :p2 " +
+                "union " +
+                "select distinct p.id as A_ID, p.first_name, p.last_name, p.birth_date, p.employed, p.occupation, p.address_id " +
+                "from Person p " +
+                "where p.id = :p3"
+
+        assertThat(selectStatement.selectStatement).isEqualTo(expected)
+
+        val records = template.selectList(selectStatement) { rs, _ ->
+            val record = PersonRecord()
+            record.id = rs.getInt(1)
+            record.firstName = rs.getString(2)
+            record.lastName = rs.getString(3)
+            record.birthDate = rs.getTimestamp(4)
+            record.employed = rs.getString(5)
+            record.occupation = rs.getString(6)
+            record.addressId = rs.getInt(7)
+            record
+        }
+
+        assertThat(records).hasSize(3)
+        with(records[0]!!) {
+            assertThat(id).isEqualTo(1)
+            assertThat(firstName).isEqualTo("Fred")
+            assertThat(lastName).isEqualTo("Flintstone")
+            assertThat(birthDate).isNotNull()
+            assertThat(employed).isEqualTo("Yes")
+            assertThat(occupation).isEqualTo("Brontosaurus Operator")
+            assertThat(addressId).isEqualTo(1)
+        }
+
+        with(records[2]!!) {
+            assertThat(id).isEqualTo(3)
+            assertThat(firstName).isEqualTo("Pebbles")
+            assertThat(lastName).isEqualTo("Flintstone")
+            assertThat(birthDate).isNotNull()
+            assertThat(employed).isEqualTo("No")
+            assertThat(occupation).isNull()
+            assertThat(addressId).isEqualTo(1)
+        }
+    }
+
     @Test
     fun testRawSelectWithJoin() {
         val selectStatement = select(