Receiving weird host can't be null error with ef core - ef-core-3.1

Question

I have recently installed the EF Core 3.1.6 on a home project using postgresql.
I have the connection string, and can add migrations easily with the Package Manager Console. If I run my application the Database.Migrate() will migrate the migrations easily. However if I attempt to update the database via the Package Manager Console with an 'update-database' I receive this error:
System.ArgumentException: Host can't be null
at Npgsql.NpgsqlConnector.Open(NpgsqlTimeout timeout, Boolean async, CancellationToken cancellationToken)
at Npgsql.NpgsqlConnection.<>c__DisplayClass32_0.<<Open>g__OpenLong|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at Npgsql.NpgsqlConnection.Open()
at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlDatabaseCreator.Exists()
at Microsoft.EntityFrameworkCore.Migrations.HistoryRepository.Exists()
at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.Migrate(String targetMigration)
at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.UpdateDatabase(String targetMigration, String contextType)
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.UpdateDatabaseImpl(String targetMigration, String contextType)
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.UpdateDatabase.<>c__DisplayClass0_0.<.ctor>b__0()
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Host can't be null
I do not know what is happening, if I am missing a nuget package, etc. Any possible help and explanation for what is happening would be greatly appreciated.

Answer 1

I Solved it. It had to do with the way I was building the connection string on runtime and not buildtime.

Answer 2

You should export your env variables first from terminal like this:
export $(grep -v '^#' ./dev.env | xargs)
{dev.env} -> change it to your env file

Answer 3

Check your connection string in your startup class you may have different connection string name with the config of the database in the startup when you are using appsetting.json
Startup configuration
appsetting.json

Answer 4

You should set ConnectionStrings in program.cs|startup.cs.
Add this into the program.cs (.net7)
builder.Services.Configure<ConnectionStrings>(
builder.Configuration.GetSection(nameof(ConnectionStrings))
);
or startup.cs (.net6):
services.Configure<ConnectionStrings>(Configuration.GetSection("ConnectionStrings"));

Answer 5

add bellow lines in Program.cs file
builder.Services.AddDbContext<ApplicationDBContext>(options =>
options.UseNpgsql(builder.Configuration.GetConnectionString("DefaultConnection")));
builder.Services.AddScoped<IDataAccessProvider, DataAccessProvider>();
and bellow connection string in appsettings.json
  "ConnectionStrings": {
    "DefaultConnection": "User ID=postgres;Password=******;Host=127.0.0.1;Port=****;Database=at;"
  },   "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*"