使用 Dapper.NET 在一次往返中执行多个 SQL 语句

Question

There is a nice feature in ADO.NET that allows you to send multiple SQL statements to database in one roundtrip and receive results for all statements:

var command = new SqlCommand("SELECT count(*) FROM TableA; SELECT count(*) FROM TableB;", connection);

using(var reader = command.ExecuteReader())
{
    reader.Read();
    resultA = reader.GetInt32(0);
    reader.NextResult();
    reader.Read();
    resultB = reader.GetInt32(0);
}

Is there a similar feature in Dapper.NET?

Answer 1

Yes, the Dapper QueryMultiple extension can do that:

string query = @"SELECT COUNT(*) FROM TABLEA;
                 SELECT COUNT(*) FROM TABLEB";
using (var multi = connection.QueryMultiple(query, null))
{
    int countA = multi.Read<int>().Single();
    int countB = multi.Read<int>().Single();
}     

According to Marc Gravell this is the ideal way to execute multiple queries in a single batch.

Note: Dapper creator Sam Saffron has posted a detailed explanation with code sample on using QueryMultiple to accomplish this.

UPDATE: I add the important comment from Marc

Note: from 1.5-ish (a little earler on the alpha builds) there is a ReadSingle() method that may be more convenient and efficient than Read().Single()

Answer 2

var grid = connection.QueryMultiple("
             SELECT COUNT(*) FROM TABLEA
             SELECT COUNT(*) FROM TABLEB
             SELECT COUNT(*) FROM TABLEC");
var lstResult = new List<int>();
var isNext = false;
do{
    var first2 = info.Read<int>().Single();
    lstResult.Add(first2);
    isNext=info.IsConsumed;
}
while (!isNext);