feat: EXPOSED-78 Support database-generated values for columns (#1844)

* feat: EXPOSED-78 Support DB-generated values for columns

This feature will enable marking a column as databaseGenerated to be able to omit setting it when inserting a new record without getting an error. The value for the column can be set by creating a TRIGGER or with a DEFAULT clause, for example.

exposed-core/api/exposed-core.api

@@ -2218,6 +2218,7 @@ public class org/jetbrains/exposed/sql/Table : org/jetbrains/exposed/sql/ColumnS
 	public fun crossJoin (Lorg/jetbrains/exposed/sql/ColumnSet;)Lorg/jetbrains/exposed/sql/Join;
 	public final fun customEnumeration (Ljava/lang/String;Ljava/lang/String;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function1;)Lorg/jetbrains/exposed/sql/Column;
 	public static synthetic fun customEnumeration$default (Lorg/jetbrains/exposed/sql/Table;Ljava/lang/String;Ljava/lang/String;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)Lorg/jetbrains/exposed/sql/Column;
+	public final fun databaseGenerated (Lorg/jetbrains/exposed/sql/Column;)Lorg/jetbrains/exposed/sql/Column;
 	public final fun decimal (Ljava/lang/String;II)Lorg/jetbrains/exposed/sql/Column;
 	public final fun default (Lorg/jetbrains/exposed/sql/Column;Ljava/lang/Object;)Lorg/jetbrains/exposed/sql/Column;
 	public final fun default (Lorg/jetbrains/exposed/sql/CompositeColumn;Ljava/lang/Object;)Lorg/jetbrains/exposed/sql/CompositeColumn;

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/Column.kt

@@ -39,6 +39,8 @@ class Column<T>(
 
     fun defaultValueInDb() = dbDefaultValue
 
+    internal var isDatabaseGenerated: Boolean = false
+
     /** Appends the SQL representation of this column to the specified [queryBuilder]. */
     override fun toQueryBuilder(queryBuilder: QueryBuilder): Unit = TransactionManager.current().fullIdentity(this@Column, queryBuilder)
 

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/Table.kt

@@ -772,6 +772,11 @@ open class Table(name: String = "") : ColumnSet(), DdlAware {
         defaultValueFun = defaultValue
     }
 
+    // Potential names: readOnly, generatable, dbGeneratable, dbGenerated, generated, generatedDefault, generatedInDb
+    fun <T> Column<T>.databaseGenerated(): Column<T> = apply {
+        isDatabaseGenerated = true
+    }
+
     /** UUID column will auto generate its value on a client side just before an insert. */
     fun Column<UUID>.autoGenerate(): Column<UUID> = clientDefault { UUID.randomUUID() }
 

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/statements/BaseBatchInsertStatement.kt

@@ -18,7 +18,7 @@ abstract class BaseBatchInsertStatement(
 
     internal val data = ArrayList<MutableMap<Column<*>, Any?>>()
 
-    private fun Column<*>.isDefaultable() = columnType.nullable || defaultValueFun != null
+    private fun Column<*>.isDefaultable() = columnType.nullable || defaultValueFun != null || isDatabaseGenerated
 
     override operator fun <S> set(column: Column<S>, value: S) {
         if (data.size > 1 && column !in data[data.size - 2] && !column.isDefaultable()) {

exposed-tests/src/test/kotlin/org/jetbrains/exposed/sql/tests/shared/entities/EntityTests.kt

@@ -1423,4 +1423,75 @@ class EntityTests : DatabaseTestsBase() {
             assertEquals(1, count)
         }
     }
+
+    object CreditCards : IntIdTable("CreditCards") {
+        val number = varchar("number", 16)
+        val spendingLimit = ulong("spendingLimit").databaseGenerated()
+    }
+
+    class CreditCard(id: EntityID<Int>) : IntEntity(id) {
+        companion object : IntEntityClass<CreditCard>(CreditCards)
+
+        var number by CreditCards.number
+        var spendingLimit by CreditCards.spendingLimit
+    }
+
+    @Test
+    fun testDatabaseGeneratedValues() {
+        withTables(excludeSettings = listOf(TestDB.SQLITE), CreditCards) { testDb ->
+            when (testDb) {
+                TestDB.POSTGRESQL, TestDB.POSTGRESQLNG -> {
+                    // The value can also be set using a SQL trigger
+                    exec(
+                        """
+                        CREATE OR REPLACE FUNCTION set_spending_limit()
+                          RETURNS TRIGGER
+                          LANGUAGE PLPGSQL
+                          AS
+                        $$
+                        BEGIN
+                            NEW."spendingLimit" := 10000;
+                            RETURN NEW;
+                        END;
+                        $$;
+                        """.trimIndent()
+                    )
+                    exec(
+                        """
+                        CREATE TRIGGER set_spending_limit
+                        BEFORE INSERT
+                        ON CreditCards
+                        FOR EACH ROW
+                        EXECUTE PROCEDURE set_spending_limit();
+                        """.trimIndent()
+                    )
+                }
+                else -> {
+                    // This table is only used to get the statement that adds the DEFAULT value, and use it with exec
+                    val creditCards2 = object : IntIdTable("CreditCards") {
+                        val spendingLimit = ulong("spendingLimit").default(10000uL)
+                    }
+                    val missingStatements = SchemaUtils.addMissingColumnsStatements(creditCards2)
+                    missingStatements.forEach {
+                        exec(it)
+                    }
+                }
+            }
+
+            val creditCardId = CreditCards.insertAndGetId {
+                it[number] = "0000111122223333"
+            }.value
+            assertEquals(
+                10000uL,
+                CreditCards.select { CreditCards.id eq creditCardId }.single()[CreditCards.spendingLimit]
+            )
+
+            val creditCard = CreditCard.new {
+                number = "0000111122223333"
+            }.apply {
+                flush()
+            }
+            assertEquals(10000uL, creditCard.spendingLimit)
+        }
+    }
 }