Could not load file or assembly MySql.Data because of mismatch reference version.

Databases > MySQL
The error "could not load file or assembly MySQL.Data" often occurs in .NET applications using MySQL as the database. It typically indicates a missing or incompatible MySQL.Data.dll file, a component essential for .NET and MySQL integration. Generally, the error message is like below:
 
Could not load file or assembly 'MySql.Data, Version=8.0.19.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
 
Understanding the error:
 
ROOT CAUSES
  • Missing MySQL.Data.dll: The DLL file is not present in the application's bin directory.
  • Incorrect Version: The application references a different version of MySQL.Data.dll than what is installed.
  • Path Issues: The application is unable to locate the DLL file due to incorrect path settings.
Resolving the error:
 
CHECKING FOR THE DLL FILE
Ensure that the MySQL.Data.dll file is present in the bin directory of your application. If missing, it needs to be added.
// Example of a using directive in C#
using MySql.Data.MySqlClient;
VERIFYING DLL VERSION
Confirm that the version of MySQL.Data.dll in your project matches the one referenced in your application's configuration file.
<configuration>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="MySql.Data" publicKeyToken="c5687fc88969c44d" culture="neutral" />
<!--
The following line depends on your own version, if you upgrade to version 9.0.0.0, please use <bindingRedirect oldVersion="0.0.0.0-9.0.0.0" newVersion="9.0.0.0" /> 
?-->
        <bindingRedirect oldVersion="0.0.0.0-8.0.0.0" newVersion="8.0.0.0" /> 
      </dependentAssembly>
    </assemblyBinding>
  </runtime>
</configuration>
Correcting Path Issues
If the DLL is present but still not loaded, check the application's path settings and ensure they are correctly configured to find the MySQL.Data.dll file.
 
Using NuGet Package Manager
Using NuGet Package Manager to install or update the MySQL.Data package ensures the correct version is added with appropriate references.
PM> Install-Package MySql.Data -Version [your-required-version]
Checking Platform Compatibility
Ensure that the MySQL.Data.dll is compatible with the platform your application is targeting, like x86 or x64.
 
Updating .NET Framework
Sometimes, updating the .NET Framework version can resolve compatibility issues with MySQL.Data.dll.
 
Advanced Troubleshooting
Using Fusion Log Viewer
Fusion Log Viewer (fuslogvw.exe) can be used to diagnose assembly binding errors in detail.
 
Checking GAC
Ensure that the correct version of MySQL.Data.dll is installed in the Global Assembly Cache (GAC) if your application relies on it.
 
Conclusion
The "could not load file or assembly MySQL.Data" error is a common issue that can usually be resolved by ensuring the correct DLL file is present, the version matches, and the application's configuration is correctly set up. Regular maintenance and updates to your .NET framework and MySQL.Data package can help prevent this issue.