feat: implement attachment database layer

- Add AttachmentInterface to main Datastore interface
- Implement CRUD operations for attachments following existing patterns
- Add proper SQL marshalling/unmarshalling with HEX/UNHEX for binary IDs
- Include soft deletion and proper indexing support

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

core/model/db/attachment.go

@@ -0,0 +1,126 @@
+package db
+
+import (
+	"database/sql"
+
+	"github.com/openaccounting/oa-server/core/model/types"
+	"github.com/openaccounting/oa-server/core/util"
+)
+
+const attachmentFields = "LOWER(HEX(id)),LOWER(HEX(transactionId)),LOWER(HEX(orgId)),LOWER(HEX(userId)),fileName,originalName,contentType,fileSize,filePath,description,uploaded,deleted"
+
+type AttachmentInterface interface {
+	InsertAttachment(*types.Attachment) error
+	GetAttachment(string, string, string) (*types.Attachment, error)
+	GetAttachmentsByTransaction(string, string) ([]*types.Attachment, error)
+	DeleteAttachment(string, string, string) error
+}
+
+func (db *DB) InsertAttachment(attachment *types.Attachment) error {
+	query := "INSERT INTO attachment(id,transactionId,orgId,userId,fileName,originalName,contentType,fileSize,filePath,description,uploaded,deleted) VALUES(UNHEX(?),UNHEX(?),UNHEX(?),UNHEX(?),?,?,?,?,?,?,?,?)"
+
+	_, err := db.Exec(
+		query,
+		attachment.Id,
+		attachment.TransactionId,
+		attachment.OrgId,
+		attachment.UserId,
+		attachment.FileName,
+		attachment.OriginalName,
+		attachment.ContentType,
+		attachment.FileSize,
+		attachment.FilePath,
+		attachment.Description,
+		util.TimeToMs(attachment.Uploaded),
+		attachment.Deleted,
+	)
+
+	return err
+}
+
+func (db *DB) GetAttachment(attachmentId, transactionId, orgId string) (*types.Attachment, error) {
+	query := "SELECT " + attachmentFields + " FROM attachment WHERE id = UNHEX(?) AND transactionId = UNHEX(?) AND orgId = UNHEX(?) AND deleted = false"
+	row := db.QueryRow(query, attachmentId, transactionId, orgId)
+
+	return db.unmarshalAttachment(row)
+}
+
+func (db *DB) GetAttachmentsByTransaction(transactionId, orgId string) ([]*types.Attachment, error) {
+	query := "SELECT " + attachmentFields + " FROM attachment WHERE transactionId = UNHEX(?) AND orgId = UNHEX(?) AND deleted = false ORDER BY uploaded DESC"
+	rows, err := db.Query(query, transactionId, orgId)
+
+	if err != nil {
+		return nil, err
+	}
+
+	return db.unmarshalAttachments(rows)
+}
+
+func (db *DB) DeleteAttachment(attachmentId, transactionId, orgId string) error {
+	query := "UPDATE attachment SET deleted = true WHERE id = UNHEX(?) AND transactionId = UNHEX(?) AND orgId = UNHEX(?)"
+	_, err := db.Exec(query, attachmentId, transactionId, orgId)
+	return err
+}
+
+func (db *DB) unmarshalAttachment(row *sql.Row) (*types.Attachment, error) {
+	attachment := &types.Attachment{}
+	var uploaded int64
+
+	err := row.Scan(
+		&attachment.Id,
+		&attachment.TransactionId,
+		&attachment.OrgId,
+		&attachment.UserId,
+		&attachment.FileName,
+		&attachment.OriginalName,
+		&attachment.ContentType,
+		&attachment.FileSize,
+		&attachment.FilePath,
+		&attachment.Description,
+		&uploaded,
+		&attachment.Deleted,
+	)
+
+	if err != nil {
+		return nil, err
+	}
+
+	attachment.Uploaded = util.MsToTime(uploaded)
+
+	return attachment, nil
+}
+
+func (db *DB) unmarshalAttachments(rows *sql.Rows) ([]*types.Attachment, error) {
+	defer rows.Close()
+
+	attachments := []*types.Attachment{}
+
+	for rows.Next() {
+		attachment := &types.Attachment{}
+		var uploaded int64
+
+		err := rows.Scan(
+			&attachment.Id,
+			&attachment.TransactionId,
+			&attachment.OrgId,
+			&attachment.UserId,
+			&attachment.FileName,
+			&attachment.OriginalName,
+			&attachment.ContentType,
+			&attachment.FileSize,
+			&attachment.FilePath,
+			&attachment.Description,
+			&uploaded,
+			&attachment.Deleted,
+		)
+
+		if err != nil {
+			return nil, err
+		}
+
+		attachment.Uploaded = util.MsToTime(uploaded)
+		attachments = append(attachments, attachment)
+	}
+
+	return attachments, nil
+}

core/model/db/db.go

@@ -15,6 +15,7 @@ type Datastore interface {
 	OrgInterface
 	AccountInterface
 	TransactionInterface
+	AttachmentInterface
 	PriceInterface
 	SessionInterface
 	ApiKeyInterface