Create SQL parameters programmatically

Question

Another annoying one for me but probably something simple.

I have a number of possible where clauses for a query based on user input, my question is how can I add these programmatically?

For instance:

wherequery = @"WHERE fieldname = @p_FieldName AND ";
if (txtValue.textLength > 0){
    wherequery += "fieldname2 = @p_FieldName2 AND ";
}
query = @"SELECT * FROM tabe" + wherequery;
sql = connection.CreateCommand();
sql.CommandText = query;

How would I go about doing the parameters for that? I've tried ArrayLists, Dictionaries and a few other methods but can't find a way of doing it. Ideally I'd want to do something like this:

SqlParameter[] sqlparams;
wherequery = @"WHERE fieldname = @p_FieldName AND ";
if (txtValue.textLength > 0){
    wherequery += "fieldname2 = @p_FieldName2 AND ";
    sqlparams.Parameters.Add("@p_FieldName2 ", SqlDbType.VarChar).Value = txtValue.text;
}
query = @"SELECT * FROM tabe" + wherequery;
sql = connection.CreateCommand();
sql.CommandText = query;
sql.Parameters.Add(sqlparams);

Answer 1

I've made a small alteration to your code, which should hopefully point you in the right direction:

    sql = connection.CreateCommand();    
    wherequery = @"WHERE fieldname = @p_FieldName ";
    sql.Parameters.Add(new SqlParameter("@p_FieldName ", "some value for fieldname"));

    if (txtValue.textLength > 0){
        wherequery += " AND fieldname2 = @p_FieldName2 ";
        sql.Parameters.Add(new SqlParameter("@p_FieldName2 ", txtValue.text));
    }
    query = @"SELECT * FROM tabe" + wherequery;

    sql.CommandText = query;