Constructor is Ambiguous error .NET Core Web API

Question

I'm new to Web API. In my .NET Core 3.1 web api I have defined 3 constructors beleiving overloading.

[Route("api/[controller]")]
[ApiController]
public class KipController : ControllerBase
{
    private readonly IConfiguration _configuration;
    private readonly IMapper _mapper;
    private readonly dbLNePMODev1Context _context;
    public KipController(IConfiguration configuration)
    {
        _configuration = configuration;
    }
    public KipController(IMapper mapper)
    {
        _mapper = mapper;
    }

    public KipController(dbLNePMODev1Context context)
    {
        _context = context;
    }
    ......

But when executing the application it says the following error

System.AggregateException HResult=0x80131500 Message=Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: epmoAPI.Models.dbLNePMODev1Context Lifetime: Scoped ImplementationType: epmoAPI.Models.dbLNePMODev1Context': Unable to activate type 'epmoAPI.Models.dbLNePMODev1Context'. The following constructors are ambiguous: Void .ctor(Microsoft.EntityFrameworkCore.DbContextOptions) Void .ctor(Microsoft.EntityFrameworkCore.DbContextOptions1[epmoAPI.Models.dbLNePMODev1Context])) Source=Microsoft.Extensions.DependencyInjection StackTrace: at Microsoft.Extensions.DependencyInjection.ServiceProvider..ctor(IEnumerable1 serviceDescriptors, ServiceProviderOptions options) at Microsoft.Extensions.DependencyInjection.ServiceCollectionContainerBuilderExtensions.BuildServiceProvider(IServiceCollection services, ServiceProviderOptions options) at Microsoft.Extensions.DependencyInjection.DefaultServiceProviderFactory.CreateServiceProvider(IServiceCollection containerBuilder) at Microsoft.Extensions.Hosting.Internal.ServiceFactoryAdapter`1.CreateServiceProvider(Object containerBuilder) at Microsoft.Extensions.Hosting.HostBuilder.CreateServiceProvider() at Microsoft.Extensions.Hosting.HostBuilder.Build() at epmoAPI.Program.Main(String[] args) in C:\Projects\Enterprise PMO\ePMOHub\epmoAPI\Program.cs:line 16

This exception was originally thrown at this call stack: [External Code]

Inner Exception 1: InvalidOperationException: Error while validating the service descriptor 'ServiceType: epmoAPI.Models.dbLNePMODev1Context Lifetime: Scoped ImplementationType: epmoAPI.Models.dbLNePMODev1Context': Unable to activate type 'epmoAPI.Models.dbLNePMODev1Context'. The following constructors are ambiguous: Void .ctor(Microsoft.EntityFrameworkCore.DbContextOptions) Void .ctor(Microsoft.EntityFrameworkCore.DbContextOptions`1[epmoAPI.Models.dbLNePMODev1Context])

Inner Exception 2: InvalidOperationException: Unable to activate type 'epmoAPI.Models.dbLNePMODev1Context'. The following constructors are ambiguous: Void .ctor(Microsoft.EntityFrameworkCore.DbContextOptions) Void .ctor(Microsoft.EntityFrameworkCore.DbContextOptions`1[epmoAPI.Models.dbLNePMODev1Context])

Please help me. I am not getting an idea whats wrong in my code

why do you have 3 constructors instead of one that take 3 arguments ? — Nadeem Khoury
– Nadeem Khoury, Commented May 7, 2020 at 11:39
Sorry I am very new to DI. So honestly no idea how to deal with it. Thats why I made it 3 — Sandeep Thomas
– Sandeep Thomas, Commented May 7, 2020 at 11:53

Sergey Kovalev · Accepted Answer · 2020-05-07 11:45:16Z

1

Your IConfiguration (and probably IMapper) use dependency injection, while dbLNePMODev1Context does not. That's why ASP.NET Core can't instantiate it.

A cleaner solution:

public KipController(IConfiguration configuration = null, IMapper mapper = null, dbLNePMODev1Context context = null)
{
    _configuration = configuration;
    _mapper = mapper;
    _context = context;
}

answered May 7, 2020 at 11:45

Sergey Kovalev

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1 Comment

Sandeep Thomas Over a year ago

Thank you. But I just tried that and its triggering System.AggregateException: 'Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: epmoAPI.Models.dbLNePMODev1Context Lifetime: Scoped ImplementationType: epmoAPI.Models.dbLNePMODev1Context': Unable to activate type 'epmoAPI.Models.dbLNePMODev1Context'. The following constructors are ambiguous: Void .ctor(Microsoft.EntityFrameworkCore.DbContextOptions) Void .ctor(Microsoft.EntityFrameworkCore.DbContextOptions`1[epmoAPI.Models.dbLNePMODev1Context]))'

HelpMeSo · Accepted Answer · 2020-05-07 18:33:38Z

If your dbLNePMODev1Context class inherits from DbContext (If your project uses EntityFrameworkCore) then you can register dbLNePMODev1Context as a DBContext in ConfigureServices method. You can add DbContextOptionsBuilder to indicate type of DB, Connection String and other details.

public void ConfigureServices(IServiceCollection services)
{
...
services.AddDbContext<dbLNePMODev1Context>();
...
}

If your dbLNePMODev1Context class does not use EntityFramework then you can just register it as a service .Please decide on Scoped,Transient or Singleton. Reference

public void ConfigureServices(IServiceCollection services)
{
...
services.AddSingleton(new dbLNePMODev1Context());
...
}

It would give a better idea if you share your ConfigureServices method from Startup.cs class.

stanimirsp · Accepted Answer · 2024-01-17 08:18:00Z

0

I suppose you are using the default ASP .NET dependency injection container and you have more than one constructor in dbLNePMODev1Context. So the DI container doesn't know which constructor to use when registering the service. Try to specify it explicitly:

services.AddScoped(serviceProvider =>
 {
    var options = serviceProvider.GetRequiredService<DbContextOptions<dbLNePMODev1Context>>();
    return new dbLNePMODev1Context(options);
 });

answered Jan 17, 2024 at 8:18

stanimirsp

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Comments

Yehor Androsov · Accepted Answer · 2024-01-17 10:12:02Z

0

[Route("api/[controller]")]
[ApiController]
public class KipController : ControllerBase
{
private readonly IConfiguration _configuration;
private readonly IMapper _mapper;
private readonly dbLNePMODev1Context _context;

public KipController(IConfiguration configuration, IMapper mapper, dbLNePMODev1Context context)
    {
        _configuration = configuration;
        _mapper = mapper;
        _context = context;
    }
     // Your other action methods go here...
}

This way, you can use any combination of the dependencies in your controller actions. Make sure to update your DI configuration accordingly in your startup class to inject these dependencies correctly.

edited Jan 17, 2024 at 10:12

Yehor Androsov

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answered Jan 17, 2024 at 10:09

Mahavirsinh Chudasama

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