Correct use of DuckDBAppender for a generic table

[brasio]

Hi all,

My question is how to use DuckDBAppender retrieving data from a generic table of database server with a datareader, without knowing at compile time field types. Is there any example or documentation?

var appender = MyDuckDBConnection.CreateAppender(mytable);
while (myserverdatareader.Read())
{
    var r = appender.CreateRow();
    for (int i = 0; i < myserverdatareader.FieldCount; i++)
    {
        r.AppendValue(myserverdatareader.GetValue(i)); // error: AppendValue does not accept object
    }
    r.EndRow();
}
appender.Close();
appender.Dispose();

mytable must be created, retrieving data types from myserverdatareader and converting them to the specific DuckDB type.
Thanks for your help!

[Giorgi]

You can do it like this:

object value = 42;
_ = value switch
{
    bool val => row.AppendValue(val),

    int val => row.AppendValue(val),
    long val => row.AppendValue(val),
};

[brasio]

Thanks. I suppose I need to include all .net data types, as in https://duckdb.net/docs/type-mapping.html

I wonder if there is a way to not evaluate object type, in switch condition, for every row, as a table column type is always the same.

[Giorgi]

You can probably create a static Dictionary<Type, Action> and use DbDataReader.GetFieldType(Int32) Method to lookup the action for appending the value.