.NET Core Informix multiple parameters in IfxCommand - .net-core

Question

This is the environment I work in:
.NET Core 3.1 (console application for testing purposes)
CSDK 4.50.FC5
Informix.Net.Core.dll from the CSDK 4.50.FC5 package
Informix Server 12.10
The problem I have is that some of the queries from my .NET Core app are executed successfully and results are retrieved from the Informix database, but sometimes I get weird errors that have to do something with parameters. Of course, I am trying to use IfxParameters in order to be safe from SQL Injection attacks.
This passes succesfully (table names and columns are made up). Here I am using positional parameters:
IfxCommand command = connection.CreateCommand();
command.CommandType = System.Data.CommandType.Text;
command.CommandText = "SELECT * FROM employees WHERE name LIKE '%John%' SKIP ? LIMIT ?";
IfxParameter paramSkip = new IfxParameter("skip", IfxType.Integer);
paramSkip.Value = 30;
command.Parameters.Add(paramSkip);
IfxParameter paramLimit = new IfxParameter("limit", IfxType.Integer);
paramLimit.Value = 10;
command.Parameters.Add(paramLimit);
connection.Open();
using (IfxDataReader reader = command.ExecuteReader())
{
... // reading data from the IfxDataReader
}
Let's see now this example which produces an error:
IfxCommand command = connection.CreateCommand();
command.CommandType = System.Data.CommandType.Text;
command.CommandText = "SELECT * FROM employees WHERE name LIKE ? SKIP 10 LIMIT ?";
IfxParameter paramSearch = new IfxParameter("searchQuery", IfxType.VarChar);
paramSearch.Value = "%John%";
command.Parameters.Add(paramSearch);
IfxParameter paramLimit = new IfxParameter("limit", IfxType.Integer);
paramLimit.Value = 10;
command.Parameters.Add(paramLimit);
con.Open();
using (IfxDataReader reader = command.ExecuteReader())
{
...
}
Error:
IfxException: ERROR [22018] [Informix][Informix ODBC Driver][Informix]A character to numeric conversion process failed
The only difference here is that I have parameters that are not of the same type. In the first example both parameters were IfxType.Integer, and now I have IfxType.Integer and IfxType.VarChar
Using named parameters doesn't help. For the following IfxCommand:
command.CommandText = "SELECT * FROM employees WHERE name LIKE '%John%' SKIP 10 LIMIT #limit";
I get the following error:
Error: IfxException: ERROR [42000] [Informix][Informix ODBC Driver][Informix]A syntax error has occurred.
I hope someone will be able to point me in the right direction in order to solve this issue. I am open to any suggestion that will solve this. If any further info is needed, please hit me up!

Answer 1

This is because of the precedence of positional parameters. "where" parameters have lower precedence than "skip" and "limit". Therefore, create the "where IfxParameter" parameters (paramSearch) at the end.
Try:
IfxCommand command = connection.CreateCommand();
command.CommandType = System.Data.CommandType.Text;
command.CommandText = "SELECT * FROM employees WHERE name LIKE ? SKIP 10 LIMIT ?";
IfxParameter paramLimit = new IfxParameter("limit", IfxType.Integer);
paramLimit.Value = 10;
command.Parameters.Add(paramLimit);
IfxParameter paramSearch = new IfxParameter("searchQuery", IfxType.VarChar);
paramSearch.Value = "%John%";
command.Parameters.Add(paramSearch);
...