private async Task <MultiTablePreview> GeneratePreview()
{
var metas = _xlsSheetMetas.Where(x => x.ToBeImported).ToList();
var tableNames = metas.Select(m => m.NewName).ToList();
// build the sql string
var prefix = Guid.NewGuid().ToString().Replace("-", "") + "_";
var sb = new StringBuilder(GetImportSql(prefix));
sb.AppendLine();
foreach (var m in metas)
{
sb.AppendLine($"SELECT * FROM {(prefix + m.NewName).DoubleQuote()} LIMIT 1000;");
sb.AppendLine($"DROP TABLE {(prefix + m.NewName).DoubleQuote()};");
}
var sql = sb.ToString();
// run it in a transaction and then roll it back so nothing is actually affected
var output = await Task.Run(() =>
_manager.ExecuteScriptEx(
code: sql,
args: new Dictionary <string, object>(),
transactionType: NotebookManager.TransactionType.RollbackTransaction,
vars: out _));
if (output.DataTables.Count != metas.Count)
{
// this shouldn't happen, it should have thrown from ExecuteScriptEx
throw new Exception("The import failed to generate all the tables.");
}
// read out the contents of each table, which we arranged to have selected in our script
return(new MultiTablePreview {
Tables = metas.Select((x, i) => (TableName: x.NewName, DataTable: output.DataTables[i])).ToList()
});