How to create DbContext

Question

below default code in controller working fine

public ProductController(appDbContext parmContext)
{
    _context = parmContext;
}

now I want to add DAL and in that, getting error creating object of type appDbContext, what to pass/set for parmContext?

below is the connection in Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    services.AddDbContext<appDbContext>(config => 
    {
        config.UseMySql(Configuration.GetConnectionString("PreSales"));
});
}

Below is the code I want to use

public IEnumerable<ProductStatusMaster> GetProductStatusFRdal()

    // here I ant to create object of DBcontext (i.e. _context)

    {
        try
            {
                 var msm = _context.ProductStatusMaster
                    .Where(s => s.ActiveYn == 1 )
                    .OrderBy(s => s.Status)
                    .ToList();

                return msm;
            }
            catch
            {
                throw;
            }
    }

Answer 1

Let me get an answer.

There are 2 ways to realize code you want. 1) Through Controller DI. 2) Through Service Locator pattern (antipattern).

By the code:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    services.AddDbContext<appDbContext>(config => 
    {
        config.UseMySql(Configuration.GetConnectionString("PreSales"));
});
}

you set up dependency for DbContext and configure connection parameters. So, for the first method you should pass the dependency through controller. Possible code will be like this:

public class MyTestAppController
{
     private appDbContext _context;

     public MyTestApController(appDbContext externalAppDbContext)
     {
         _context = externalAppDbContext;
     }

     public IEnumerable<ProductStatusMaster> GetProductStatusFRdal()
     {
        try
            {
                 var msm = _context.ProductStatusMaster
                    .Where(s => s.ActiveYn == 1 )
                    .OrderBy(s => s.Status)
                    .ToList();

                return msm;
            }
            catch
            {
                throw;
            }
    }
}

2) Using Service Locator pattern

In this case you should use IServiceProvider dependency. Code example like this:

public class MyTestAppController
{
   private IServiceProvider _provider; 

   public MyTestAppController(IServiceProvider provider) => _provider = provider; 

   public IEnumerable<ProductStatusMaster> GetProductStatusFRdal() 
   {
      var _context = _provider.GetService<appDbContext>(); 

      try 
      { 
           var msm = _context.ProductStatusMaster .Where(s => s.ActiveYn == 1 ) 
                     .OrderBy(s => s.Status) .ToList(); return msm; 
      } 
      catch { throw; }
   }
}