使用Npgsql更新数据库/移除迁移时出现Couldn't set databaseconfig错误

场景还原 #

配置基于EntityFrameworkCore和PostgreSQL（Npgsql驱动）的.NET项目，数据库通过Docker容器部署并已用脚本完成初始化（数据库、用户、模式均已正常创建）。执行ef migrations add成功生成迁移文件，但执行update-database或remove-migration时抛出以下错误：

System.ArgumentException: Couldn't set databaseconfig (Parameter 'databaseconfig')
---> System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
at Npgsql.NpgsqlConnectionStringBuilder.GeneratedSetter(String keyword, Object value)
at Npgsql.NpgsqlConnectionStringBuilder.set_Item(String keyword, Object value)
--- End of inner exception stack trace ---
at Npgsql.NpgsqlConnectionStringBuilder.set_Item(String keyword, Object value)
at System.Data.Common.DbConnectionStringBuilder.set_ConnectionString(String value)
at Npgsql.NpgsqlConnectionStringBuilder..ctor(String connectionString)
at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlDatabaseCreator.Exists(Boolean async, CancellationToken cancellationToken)
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 connectionString, String contextType)
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.UpdateDatabaseImpl(String targetMigration, String connectionString, String contextType)
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.UpdateDatabase.<>c__DisplayClass0_0.<.ctor>b__0()
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)

错误原因 #

DatabaseConfig类中生成的连接字符串使用了错误的参数名：DatabaseConfig={Name}，而Npgsql的连接字符串规范中不存在databaseconfig这个关键字，正确的数据库名称参数应为Database或DatabaseName。

解决方案 #

修改DatabaseConfig类的ConnectionString属性，将错误的参数名替换为Database：

public class DatabaseConfig
{
  public string Host { get; set; }
  public int Port { get; set; }
  public string Schema { get; set; }
  public string Name { get; set; }
  public string User { get; set; }
  public string Password { get; set; }

  public string ConnectionString
  {
    get { return $"Server={Host},{Port};Database={Name};User Id={User};Password={Password};SearchPath={Schema}"; }
  }
}

额外优化建议 #

1. 上下文类MyContext中的OnConfiguring方法属于重复配置，因为已经在Startup.ConfigureDatabase中通过AddDbContext指定了连接字符串和命名约定，可以移除该方法，避免冲突：

public class MyContext : DbContext
{
  private readonly DatabaseConfig databaseConfig;

  public DbSet<Brand> Brands { get; set; }

  public MyContext(DbContextOptions<MyContext> options, DatabaseConfig databaseConfig)
    : base(options) => this.databaseConfig = databaseConfig;

  protected override void OnModelCreating(ModelBuilder modelBuilder)
  {
    modelBuilder.HasDefaultSchema(databaseConfig.Schema);
  }
}

2. 连接字符串中添加SearchPath={Schema}，明确指定默认搜索的数据库模式，与上下文的HasDefaultSchema配置保持一致。

内容的提问来源于stack exchange，提问作者chenny