fix: add error for multiple rows found

errors.go

@@ -51,4 +51,6 @@ var (
 	ErrForeignKeyViolated = errors.New("violates foreign key constraint")
 	// ErrCheckConstraintViolated occurs when there is a check constraint violation
 	ErrCheckConstraintViolated = errors.New("violates check constraint")
+	// ErrMultipleRecordsFound occurs when more than one record found with Only
+	ErrMultipleRecordsFound = errors.New("multiple records found")
 )

finisher_api.go

@@ -181,7 +181,7 @@ func (db *DB) Only(dest interface{}, conds ...interface{}) (tx *DB) {
 	}
 
 	if count > 1 {
-		findTx.AddError(fmt.Errorf("expected exactly one record, but found %d", count))
+		findTx.AddError(ErrMultipleRecordsFound)
 	}
 
 	return findTx