InvalidOperationException：没有为此DbContext配置数据库提供程序。 可以通过覆盖DbContext来配置提供程序

Question

I am working on project with no repository pattern. I am trying to seperate my business logic from controllers, kind of setting up a business layer. I do the following to get all of my users.

DbContext

public class DatabaseContext : DbContext
{
    public DatabaseContext() : base() { }
    public DatabaseContext(DbContextOptions options) : base(options) { }
    public DbSet<User> Users { get; set; }
    public DbSet<OvertimeRequest> OvertimeRequests { get; set; }
    public DbSet<HolidayRequest> HolidayRequests { get; set; }
    public DbSet<PaymentRequest> PaymentRequests { get; set; }
}

OvertimeRequestBusiness

public class OvertimeRequestBusiness
{
    public static OvertimeRequestBusiness Instance { get; } = new 
        OvertimeRequestBusiness();

    public OvertimeRequestBusiness() { }

    public async Task<List<User>> GetAllUsersAsync()
    {
        using (var ctx = new DatabaseContext())
        {
            var query = ctx.Users;
            var res = await query.ToListAsync();
            return res;
        }
    }
}

Controller

[Route("users"), HttpGet]
public async Task<List<User>> GetAllUsers()
{
    return await OvertimeRequestBusiness.Instance.GetAllUsersAsync();
}

And the error I get is

InvalidOperationException: No database provider has been configured for this DbContext. A provider can be configured by overriding the DbContext.OnConfiguring method or by using AddDbContext on the application service provider. If AddDbContext is used, then also ensure that your DbContext type accepts a DbContextOptions<TContext> object in its constructor and passes it to the base constructor for DbContext**

Answer 1

Without changing the OvertimeRequestBusiness is to set db connection string in OnCongfiguring method of DbContext class :

1. Setting connect string in `appsettings.json :

    "ConnectionStrings": { "MyConnectionString": "Server=(localdb)\\\\mssqllocaldb;Database=RazorPagesMovieContext-1234;Trusted_Connection=True;MultipleActiveResultSets=true" }, 

2. Create Setting.cs :

    public class Setting { public static string ConnectionString { get; set; } } 

3. Config the connectstring in Startup.cs :

    Setting.ConnectionString = Configuration.GetSection("ConnectionStrings:MyConnectionString").Value; 

4. Modify the DatabaseContext :

    public class DatabaseContext : DbContext { public DbSet<User> Users { get; set; } public DbSet<OvertimeRequest> OvertimeRequests { get; set; } public DbSet<HolidayRequest> HolidayRequests { get; set; } public DbSet<PaymentRequest> PaymentRequests { get; set; } protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) { if (!optionsBuilder.IsConfigured) { optionsBuilder.UseSqlServer(Setting.ConnectionString); } } } 

But the common way is to use DbContext with dependency injection :

https://docs.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext

Answer 2

Your DatabaseContext constructor needs to point to the connection string.

Change it to be

public class DatabaseContext : DbContext
{
    // Tell DbContext to look for the "MyConnectionString" in .config.
    public DatabaseContext() : base("MyConnectionString") { }

    public DatabaseContext(DbContextOptions options) : base(options) { }

    public DbSet<User> Users { get; set; }
    public DbSet<OvertimeRequest> OvertimeRequests { get; set; }
    public DbSet<HolidayRequest> HolidayRequests { get; set; }
    public DbSet<PaymentRequest> PaymentRequests { get; set; }
}

Where your connection string is in web.config

<configuration>
    <connectionStrings>
        <add name="MyConnectionString" providerName="System.Data.SqlClient" connectionString="Server=.\SQLEXPRESS;Initial Catalog=ABC;Integrated Security=True;MultipleActiveResultSets=true"></add>
    </connectionStrings>
</configuration>

Answer 3

I deleted the default parameterless constructor of DbContext and then passed the DbContextBuilderOption as parameter in OvertimeRequestBusiness. This did the trick for me.

OvertimeRequestBusiness Looks like this now

 public class OvertimeRequestBusiness
    {
        public static OvertimeRequestBusiness Instance { get; } = new OvertimeRequestBusiness();

        DbContextOptionsBuilder<DatabaseContext> _optionsBuilder;


        public OvertimeRequestBusiness() {
            var optionsBuilder = new DbContextOptionsBuilder<DatabaseContext>();
            optionsBuilder.UseSqlServer(@"ConnectionString");
            _optionsBuilder = optionsBuilder;
        }
  public async Task<List<User>> GetAllUsersAsync()
        {
            using (var ctx = new DatabaseContext(_optionsBuilder.Options))
            {
                var query = ctx.Users;
                var res = await query.ToListAsync();
                return res;
            }
        }

    }