MySQL Bugs: #90149: NET.Core C# MySqlParameter value returns null

Bug #90149	NET.Core C# MySqlParameter value returns null
Submitted:	20 Mar 2018 19:29	Modified:	23 Nov 2021 16:16
Reporter:	Karl Krieger	Email Updates:
Status:	Won't fix	Impact on me:	None
Category:	Connector / NET	Severity:	S2 (Serious)
Version:	6.10.6	OS:	Windows (Windows 10 64 bit)
Assigned to:		CPU Architecture:	Any
Tags:	C#, core, MySQL, MySqlParameter, NET

Description:
MySqlParameter value is assigned but still returns null when read. This happens if value which was assigned is local constant.

How to repeat:
Here's a c# code to replicate the problem (Read comment descriptions below).

static void Main(string[] args){          
    Test();
}

private static void Test() {
    uint value_a = 0;
    const uint value_b = 0; //This is the failing case

    MySqlParameter a = new MySqlParameter("a", value_a);
    MySqlParameter b = new MySqlParameter("b", value_b);

    DebugTest(a);
    DebugTest(b);
}

private static void DebugTest(MySqlParameter par) {
    string name = par.ParameterName == null ? "NULL" : par.ParameterName;
    string value = par.Value == null ? "NULL" : par.Value.ToString();

    Console.WriteLine(string.Format("name: {0}  value: {1}", name, value));

    //Expected debug for both entries is:
    //    "a"  0
    //    "b"  0

    //Resulting debug we get
    //    "a"  0
    //    "b"  NULL  <---*ERROR*
}

Additional Info
    * Visual Studio 2017 community edition
    * Net core 2.0 c# application
    * I added library Mysql.Data (6.10.6) using NuGet

This looks like a C# compiler overload resolution problem, not necessarily a Connector/NET issue (although it's facilitated by problematic API design).

This code invokes the MySqlParameter(string parameterName, MySqlDbType dbType) overload, with an argument value of MySqlDbType.Decimal (== 0).

MySqlParameter b = new MySqlParameter("b", value_b);

A workaround is to explicitly invoke the MySqlParameter(string parameterName, object value) overload:

MySqlParameter b = new MySqlParameter("b", (object) value_b);

I don't know why MySqlDbType is a better overload resolution match for a const uint. You could ask on Stack Overflow (or file a bug on Roslyn but I suspect it's either by design or a long-standing decision that can't be changed for backwards compatibility reasons).

Interesting, wonder why not introduce overloads for basic primitive types, as db itself is strongly typed.
Same like for MySqlDataReader.GetUInt() leaving option for developer to cast manually MySqlDataReader["name"], that would also save useless casting to object and back (if its being re-resolved from passed object type).

Hello Karl Krieger,

Thank you for the bug report.
Verified based on internal discussion with dev's.

Thanks,
Chiranjeevi.

Posted by developer:
 
This is a C# compiler overload resolution issue hence it is not possible to fix in Connector/NET end.
There are more overloads available to get to the desired result.