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Franqo Balsamo
Asked: 2020-08-30 04:32:48 +0800 CST 2020-08-30 04:32:48 +0800 CST

conversion error

  • 772

I have this data in SQLServer:

Title that is in float

I am making a query in c# mvc to load this data but the truth is that it is giving me a conversion error, does anyone know how to convert correctly?

Class: 

public class ProvidusCuotas{
        private float titulo { get; set; }
        private string nombre { get; set; }
        private string cuota { get; set; }
        public ProvidusCuotas(float titulo, string nombre, string cuota) {
            this.titulo = titulo;
            this.nombre = nombre;
            this.cuota = cuota;
        }
        public ProvidusCuotas() {}
    }

Model:

public List<ProvidusCuotas> cargarDatos(){
            List<ProvidusCuotas> salida = new List<ProvidusCuotas>();
            SqlConnection conn = new SqlConnection("cadenadeConexion");
            conn.Open();
            SqlCommand comand = new SqlCommand("SELECT titulo, apellido +', '+nombre,max(Cuota) FROM V_CuetaWeb GROUP BY titulo, apellido, nombre ORDER BY titulo ASC", conn);
            SqlDataReader dr = comand.ExecuteReader();
            while (dr.Read()){
                float titulo = Convert.ToSingle(dr.GetFloat(0));//aquí es donde sale el error de conversión
                string nombre = dr.GetString(1);
                string cuota = Convert.ToString(dr.GetDouble(2));
                ProvidusCuotas p = new ProvidusCuotas(titulo,nombre, cuota);
                salida.Add(p);
            }
            conn.Close();
            return salida;
        }

Mistake:System.InvalidCastException: 'La conversión especificada no es válida.'

Attached image of the view:

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c#

2 Answers

  1. Best Answer

    I advise changing the code to use the names of the fields instead of the indexes

    public List<ProvidusCuotas> cargarDatos()
{
    List<ProvidusCuotas> salida = new List<ProvidusCuotas>();

    using(SqlConnection conn = new SqlConnection("cadenadeConexion"))
    {
        conn.Open();

        string query = @"SELECT titulo, apellido +', '+nombre as fullname, max(Cuota) as cuotas
                        FROM V_CuetaWeb 
                            GROUP BY titulo, apellido, nombre 
                        ORDER BY titulo ASC";
        SqlCommand comand = new SqlCommand(query, conn);
        SqlDataReader dr = comand.ExecuteReader();

        while (dr.Read()){
            float titulo = Convert.ToSingle(dr["titulo"]);
            string nombre = dr["fullname"].ToString();
            string cuota = dr["cuotas"].ToString();

            ProvidusCuotas p = new ProvidusCuotas(titulo,nombre, cuota);
            salida.Add(p);
        }
    }

    return salida;
}

    by using the names you avoid problems that could be related to an incorrect reference

    Something that if I notice you should evaluate is because a field titulois numeric, while one that it represents cuotasis a string, I think you should do the opposite, the quotas are numeric

    you can always use thetryparse()

    float titulo = 0;
if(single.TryParse(dr["titulo"].ToString(), out titulo)){
   //si ingresa aqui es que no puedo convertir
};
    • 3

  2. I see 3 things in your problem:

    1. The proper conversion for a float data type from SQL to C# is "Double", see this documentation: https://docs.microsoft.com/en-us/dotnet/framework/data/adonet/sql-server-data- type-mappings

    2. When you pass the data from the DataReader for the title, you are converting to "Single", you should do "Convert.ToDouble(xxx)".

    3. You should check if the data is = a DbNull.

    • 1