ConfigurationManager在添加迁移时用于提取数据库连接字符串时返回null [英] ConfigurationManager return null when using to extract database connection string when add migration

问题描述

我在我的 .NET Core 控制台应用程序中使用 Entity Framework Core.我将连接字符串存储在 App.config 文件中，并在上下文类中使用 ConfigurationManager 来访问连接字符串.

I am using Entity Framework Core in my .NET Core console app. I store my connection string in the App.config file and use ConfigurationManager in context class to access the connection string.

当我想向我的项目添加新迁移时，出现以下错误:

When I want to add new migration to my project I get the following error:

System.NullReferenceException:未将对象引用设置为对象的实例.

System.NullReferenceException: Object reference not set to an instance of an object.

在 EF_tut.Context.OnConfiguring(DbContextOptionsBuilder optionsBuilder) in C:..Context.cs:line 12
在 Microsoft.EntityFrameworkCore.DbContext.get_InternalServiceProvider()
在 Microsoft.EntityFrameworkCore.Internal.InternalAccessorExtensions.GetService[TService](IInfrastructure1 accessor)
在 Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func1 factory)在 Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)在 Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)在 Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)在 Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.b__0()在 Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)

at EF_tut.Context.OnConfiguring(DbContextOptionsBuilder optionsBuilder) in C:..Context.cs:line 12
at Microsoft.EntityFrameworkCore.DbContext.get_InternalServiceProvider()
at Microsoft.EntityFrameworkCore.Internal.InternalAccessorExtensions.GetService[TService](IInfrastructure1 accessor)
at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func1 factory) at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType) at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.b__0() at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)

未将对象引用设置为对象的实例.

Object reference not set to an instance of an object.

这是我的 App.config 文件:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <connectionStrings>
         <add name="EfTutDb" 
              connectionString="Data Source=.;Initial Catalog=EF_tut;Integrated Security=True;"/>
    </connectionStrings>
</configuration>

这是我的上下文类:

class Context : DbContext
{
    public DbSet<Student> Students { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(ConfigurationManager.ConnectionStrings["EfTutDb"].ConnectionString); // Line 12.
    }
}

当我尝试在 main 方法中使用 ConfigurationManger 获取连接字符串时，我得到了连接字符串，但是当我添加迁移时，我得到了空引用错误.

When I try get connection string using ConfigurationManger in the main method, I get the connection string but when I add migration, I get Null Reference error.

推荐答案

也许这有点解决方法..但这会奏效:

Maybe it's a bit workaround.. but this will work:

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        var configuration = new ConfigurationBuilder()
            .SetBasePath(AppDomain.CurrentDomain.BaseDirectory)
            .AddXmlFile("App.config")
            .Build(); 

        optionsBuilder.UseSqlServer(configuration.GetValue<string>("connectionStrings:add:EfTutDb:connectionString"));
    }
}

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