How to detect when project is run by Add-Migration

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04-09-2024

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Detecting When a .NET Core Project is Run by Add-Migration

Running Add-Migration in your .NET Core project often triggers the execution of your startup project's code. This can lead to unwanted actions, especially if the code is specific to a running application and not intended for migration generation. This article explores how to identify when your project is being executed by the Entity Framework Core (EF Core) migration tool.

The Issue

As highlighted in a Stack Overflow question by user "S.M.", running Add-Migration can cause the startup project to execute, potentially triggering unwanted actions.

The Solution

While there's no direct flag or environment variable to indicate that the project is being run by Add-Migration, we can leverage a clever workaround suggested by user "Ivan Stoev".

Identifying the Calling Process

The key to detecting the Add-Migration process lies in understanding the parent process that launches our application. By checking the parent process's executable name, we can identify if it's the EF Core migration tool. Here's a code example:

using System.Diagnostics;

// ...

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    // ...

    // Check the calling process's name
    var callingProcessName = Process.GetCurrentProcess().Parent?.ProcessName;
    if (callingProcessName == "dotnet")
    {
        // Likely called by the EF Core migration tool
        // Skip code that should not execute during migrations
    }
    else
    {
        // Regular application startup, execute normal code
    }

    // ...
}

Explanation

1. We import the System.Diagnostics namespace for process-related operations.
2. Within the Configure method (or any other suitable entry point), we obtain the current process and its parent process using Process.GetCurrentProcess().Parent.
3. We check if the parent process's name is "dotnet." This is a common indicator that the project is being launched by the EF Core migration tool.
4. If the parent process name is "dotnet," we can skip code that should not execute during migrations. Otherwise, we proceed with the regular startup code.

Additional Considerations

• This approach assumes that the EF Core migration tool is executed using the dotnet command.
• The dotnet command might be used for other purposes, so it's crucial to carefully consider the context and the specific code that you wish to skip.
• For production deployments, you might need a more robust solution that doesn't rely on the parent process name. Consider using environment variables or specific configuration settings to control the behavior of your application based on the execution context.

Example

Let's say you have a piece of code in your Configure method that sends a welcome email to new users. You only want this code to execute when the application is running normally, not during migrations. You can use the above approach to conditionally execute this code:

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    // ...

    // Check the calling process's name
    var callingProcessName = Process.GetCurrentProcess().Parent?.ProcessName;
    if (callingProcessName == "dotnet")
    {
        // Skip email sending during migrations
    }
    else
    {
        // Send welcome email to new users
        // ... 
    }

    // ...
}

Conclusion

By utilizing the parent process name, we can effectively determine whether our .NET Core project is being executed by the EF Core migration tool. This allows us to control the behavior of our application based on the execution context, ensuring that sensitive or unnecessary code is not triggered during migrations.

Remember to carefully consider the limitations and potential risks of this approach and adapt it to your specific needs and project environment.