Question

I need to write a method in C# to save all rows in a given datatable back to the database, but I cannot depend on the rowstate of each row. I can’t think of how best to do this without extensive looping through the database table data or constant database querying.

I want to essentially perform the following insert / update for each row in the datatable, but more efficiently:

INSERT INTO table
(   col1,
    col2    )
SELECT
    'value1',
    'value2'
FROM dual
WHERE NOT EXISTS ( SELECT * FROM table WHERE col1 = 'value1' );

UPDATE table
SET col2 = 'value2'
WHERE col1 = 'value1';

I was thinking a structure like this would be the most efficient:

private void SaveDataTable(DataTable dataTable)
{
    //Remove data from the dataTable where it already exists in the database

    //Determine if the values are to be inserted or updated

    //Save relevant data
}

Any ideas on how best to accomplish this?

Answer 1

While I am unable to avoid querying for each row in the given datatable, I think this will work for now. Thanks for your responses; they were all very helpful.

(Oracle specific):

internal override bool RecordExists(DataRow row)
{
    string query = string.Concat("SELECT 1 FROM ", row.Table.TableName, " ", GetDbTableFilter(row, row.Table.PrimaryKey), " AND ROWNUM = 1");

    using(OracleCommand cmd = new OracleCommand(query, (OracleConnection)_connectionLibrary.CurrentConnection))
        using(OracleDataReader reader = cmd.ExecuteReader())
            return (reader != null && reader.Read());
}

internal override string GetDbTableFilter(DataRow row, DataColumn[] columns)
{
    string filter = "";

    foreach (DataColumn column in columns)
    {
        if (!string.IsNullOrEmpty(filter))
            filter += " AND ";

        if (string.IsNullOrEmpty(row[column].ToString()))
        {
            filter += string.Concat("(", column.ColumnName, " IS NULL OR TRIM(", column.ColumnName, ") = '')");
            continue;
        }

        if (column.DataType.Equals(typeof(DateTime)))
        {
            filter += string.Concat(column.ColumnName, " = TO_DATE('", row[column].ToString(), "')");
            continue;
        }

        filter += string.Concat(column.ColumnName, " = '", row[column].ToString(), "'");
    }

    return string.Concat("WHERE ", filter);
}

public override void SaveDataTable(DataTable dataTable)
{
    dataTable.AcceptChanges();

    foreach (DataRow row in dataTable.Rows)
        if(RecordExists(row))
            row.SetModified();
        else
            row.SetAdded();

    using (OracleDataAdapter adapter = new OracleDataAdapter(string.Format("SELECT * FROM {0}", dataTable.TableName), (OracleConnection)_connectionLibrary.CurrentConnection))
        using (OracleCommandBuilder commandBuilder = new OracleCommandBuilder(adapter))
        {
            commandBuilder.SetAllValues = true;
            commandBuilder.ConflictOption = ConflictOption.OverwriteChanges;

            adapter.InsertCommand = commandBuilder.GetInsertCommand(true);
            adapter.UpdateCommand = commandBuilder.GetUpdateCommand(true);

            adapter.Update(dataTable);
        }
}