feat: 支持 Option<T> 字段(None↔NULL)、列命名默认原样(Keep)、迁移同名列先删后加,版本 1.1.0

src/migrations/Migrator.cj

@@ -48,11 +48,30 @@ public class Migrator {
                 m.up(builder)
                 let factory = DdlFactory()
                 for (op in builder.operations) {
-                    let stmt = conn.prepareStatement(factory.toSql(op, _dialect))
-                    try {
-                        stmt.update()
-                    } finally {
-                        stmt.close()
+                    let sqls = ArrayList<String>()
+                    let isColumnOp = match (op.kind) {
+                        case MigrationOperationKind.AddColumn |
+                            MigrationOperationKind.AlterColumn => true
+                        case _ => false
+                    }
+                    if (isColumnOp) {
+                        // 同名列类型变更时先删后加（见 DdlFactory.resolveColumnSqls）
+                        let col = op.column.getOrThrow()
+                        let resolved = factory.resolveColumnSqls(op, _dialect,
+                            columnTypeInDb(conn, op.tableName, col.name))
+                        for (s in resolved) {
+                            sqls.add(s)
+                        }
+                    } else {
+                        sqls.add(factory.toSql(op, _dialect))
+                    }
+                    for (sql in sqls) {
+                        let stmt = conn.prepareStatement(sql)
+                        try {
+                            stmt.update()
+                        } finally {
+                            stmt.close()
+                        }
                     }
                 }
                 recordApplied(conn, m)
@@ -153,6 +172,26 @@ public class Migrator {
         }
     }
 
+    /// 查询库中某列的数据类型（information_schema.data_type）；列不存在返回 None。
+    /// 执行 addColumn/alterColumn 前调用，用于识别"同名列修改数据结构"场景。
+    private func columnTypeInDb(conn: Connection, table: String, column: String): ?String {
+        let stmt = conn.prepareStatement(
+            "SELECT data_type FROM information_schema.columns WHERE table_schema = current_schema() " +
+            "AND table_name = ? AND column_name = ?")
+        try {
+            stmt.set<String>(0, table)
+            stmt.set<String>(1, column)
+            let rs = stmt.query()
+            if (rs.next()) {
+                rs.getOrNull<String>(0)
+            } else {
+                None
+            }
+        } finally {
+            stmt.close()
+        }
+    }
+
     private func resolveTarget(appliedList: ArrayList<Migration>, target: String): Int64 {
         var exact: Int64 = -1
         let prefixHits = ArrayList<Int64>()