ExecuteScalar not returning right values C#

问题

Let me start by posting my code first:

ExecuteScalar method:

public T ExecuteScalar<T>(string sql, CommandType commandType, List<NpgsqlParameter> parameters)
{
    using (NpgsqlConnection conn = Konekcija_na_server.Spajanje("spoji")) 
    {
        return Execute<T>(sql, commandType, c =>
        {
            var returnValue = c.ExecuteScalar();
            return (returnValue != null && returnValue != DBNull.Value && returnValue is T)
             ? (T)returnValue 
             : default(T); 
        }, parameters);

    }        
}

Execute method:

 T Execute<T>(string sql, CommandType commandType, Func<NpgsqlCommand, T> function, List<NpgsqlParameter> parameters)
    {
        using (NpgsqlConnection conn = Konekcija_na_server.Spajanje("spoji")) 
        {
            using (var cmd = new NpgsqlCommand(sql, conn))
            {
                cmd.CommandType = commandType;
                if (parameters.Count > 0 ) 
                {
                    foreach (var parameter in parameters) 
                    {
                        cmd.Parameters.AddWithValue(parameter.ParameterName,parameter.Value);
                    }
                }
                return function(cmd);
            }

        }

    }

Call of ExecuteScalar method:

komanda = "begin;select count(*) from radni_sati where ime=@ime and prezime=@prezime" +
                      " and (dolazak is not null and odlazak is not null and sati_rada is not null) and napomena='' ;commit;";
            listaParametara.Add(new NpgsqlParameter { ParameterName = "@ime", Value = ime });
            listaParametara.Add(new NpgsqlParameter { ParameterName = "@prezime", Value = prezime });
            var nePrazni_redovi=instanca.ExecuteScalar<int>(komanda, CommandType.Text, listaParametara); 
            listaParametara.Clear();

Now my problem is when I call ExecuteScalar().

For some reason my ExecuteScalar always returns 0 as result and that can't be coz I tested it as a normal query in PSQL Shell and it always returns values>0 when I call legit query that has to return normal value.

First time It enters ExecuteScalar after a call, returns a returnValue from lamba operator and for example its 16, then when it goes to Execute function, somehow it returns 0 and I dont understand why, coz main thing I need ExecuteScalar for is to return count(*) value out as an int.

回答1:

can you tell us how are you calling ExecuteScalar? What type is T? Also, set breakpoint to: var returnValue = c.ExecuteScalar(); and check what type is returned after you step over that line (F10). In watch window of Visual Studio you should check Type column.

来源：https://stackoverflow.com/questions/46629568/executescalar-not-returning-right-values-c-sharp

标签

function

lambda

executescalar