Add updated at support for postgres datetime column

Author: ammodev

src/main/kotlin/dev/slne/surf/database/table/AuditableLongIdTable.kt

@@ -3,11 +3,61 @@ package dev.slne.surf.database.table
 import dev.slne.surf.database.columns.time.CurrentOffsetDateTime
 import dev.slne.surf.database.columns.time.offsetDateTime
 import org.jetbrains.exposed.v1.core.dao.id.ULongIdTable
+import org.jetbrains.exposed.v1.core.vendors.PostgreSQLDialect
+import org.jetbrains.exposed.v1.core.vendors.currentDialect
+import org.jetbrains.exposed.v1.r2dbc.transactions.TransactionManager
 
 open class AuditableLongIdTable(name: String = "") : ULongIdTable(name) {
     val createdAt = offsetDateTime("created_at")
         .defaultExpression(CurrentOffsetDateTime())
     val updatedAt = offsetDateTime("updated_at")
         .defaultExpression(CurrentOffsetDateTime(true))
-}
 
+    /**
+     * Appends the PostgreSQL trigger that keeps [updatedAt] in sync on every `UPDATE`.
+     *
+     * MariaDB/MySQL express this inline via `ON UPDATE CURRENT_TIMESTAMP` (see
+     * [dev.slne.surf.database.columns.time.CurrentTimestampBase]), but PostgreSQL has no such
+     * column clause, so a `BEFORE UPDATE` trigger is required instead. Returning the extra DDL from
+     * here means Exposed's `SchemaUtils.create`/`createMissingTablesAndColumns` create the trigger
+     * automatically together with the table for every subclass. On any other dialect only the base
+     * statements are returned.
+     */
+    override fun createStatement(): List<String> {
+        val statements = super.createStatement()
+        if (currentDialect !is PostgreSQLDialect) return statements
+
+        val tr = TransactionManager.current()
+        val tableIdentity = tr.identity(this)
+        val updatedAtColumn = tr.identity(updatedAt)
+        val triggerName = tr.db.identifierManager.cutIfNecessaryAndQuote(
+            "${tableName.substringAfterLast('.')}_set_updated_at"
+        )
+
+        // Shared, idempotent trigger function. Mirrors CurrentTimestampBase by storing the UTC
+        // wall-clock so the value stays consistent with the UTC instants written by the app.
+        // Every AuditableLongIdTable names the column `updated_at`, so the single shared function
+        // is consistent across tables.
+        val createFunction = """
+            CREATE OR REPLACE FUNCTION $UPDATED_AT_FUNCTION() RETURNS trigger AS $$
+            BEGIN
+                NEW.$updatedAtColumn := (CURRENT_TIMESTAMP AT TIME ZONE 'UTC');
+                RETURN NEW;
+            END;
+            $$ LANGUAGE plpgsql
+        """.trimIndent()
+
+        // DROP + CREATE keeps it idempotent across re-runs without requiring PostgreSQL 14's
+        // `CREATE OR REPLACE TRIGGER`.
+        val dropTrigger = "DROP TRIGGER IF EXISTS $triggerName ON $tableIdentity"
+        val createTrigger = "CREATE TRIGGER $triggerName BEFORE UPDATE ON $tableIdentity " +
+            "FOR EACH ROW EXECUTE FUNCTION $UPDATED_AT_FUNCTION()"
+
+        return statements + createFunction + dropTrigger + createTrigger
+    }
+
+    companion object {
+        /** Name of the shared `plpgsql` function backing the `updated_at` trigger on PostgreSQL. */
+        private const val UPDATED_AT_FUNCTION = "surf_set_updated_at"
+    }
+}