NextResult with Dapper

Question

NextResult with Dapper

c# clickhouse dapper

Question

I am using Dapper with ClickHouse database (https://clickhouse.yandex/). This is distributed column-oriented database. It works well, but query result can be divided into many blocks, so I should use NextResult to retrieve all data. Sample code:

public static void ExecuteSQL(ClickHouseConnection connection, string sql)
{
    using (var reader = connection.CreateCommand(sql).ExecuteReader())
    {
        do
        {
            while (reader.Read())
            {
                        ...
            }
        }
        while (reader.NextResult());
    }
}

I'm trying to use Dapper. In order to call NextResult I should use QueryMultiple method. I made the code:

public static void ExecuteDapperQuery<T>(ClickHouseConnection connection, string sql)
{
    Dapper.DefaultTypeMap.MatchNamesWithUnderscores = true;
    using (var dapperQuery = connection.QueryMultiple(sql))
    {
        do
        {
            var list = dapperQuery.Read<T>().ToList();
            ... /* Do something with list */
        }
        while (true);
    }
}

but this code throws exception ObjectDisposedException when all data are retrieved and SQL reader becomes null. I need to know is there the way to know when I should finish iteration? Or is there any other way to work with that database?

Alex V

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Nkosi · Accepted Answer · 8/22/2017 10:22:34 AM

It is because of the infinite do/while loop. You can only call read for the number of statements executed.

I need to know is there the way to know when I should finish iteration?

Check to make sure the reader has not already been consumed before reading the set

using (var gridReader = connection.QueryMultiple(sql)) {
    while(!gridReader.IsConsumed) { //<-- query multiple until consumed
        var list = gridReader.Read<T>().ToList();
        ... /* Do something with list */
    }
}

NextResult with Dapper

Question

Fastest Dapper Plus Extensions

Accepted Answer

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Expression Evaluator