EF Core租户查询过滤器扩展方法切换租户失效问题求助

问题现象 #

在EF Core实现租户查询过滤器时，最初在ApplicationDbContext内编写私有方法SetTenantQueryFilter，生成的SQL会将CurrentUserId作为参数传递，切换租户功能正常。但将该逻辑封装为ModelBuilder的扩展方法后，生成的SQL直接硬编码租户ID，导致切换租户时过滤器未更新，即使尝试从OnModelCreating传入UserService也无效。

原正常代码 #

public class ApplicationDbContext : DbContext
{
    private readonly IUserService userService;

    public ApplicationDbContext(DbContextOptions options) : base(options)
        => userService = DbContextExtension.ServiceCollection.CheckService<IUserService>();

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        SetTenantQueryFilter<ClassRoom>(builder);
        SetTenantQueryFilter<Course>(builder);
        SetTenantQueryFilter<Demo>(builder);
        SetTenantQueryFilter<Student>(builder);
        SetTenantQueryFilter<Teacher>(builder);
    }

    private void SetTenantQueryFilter<TEntity>(ModelBuilder builder) where TEntity : class, IUserIsolation
        => builder.Entity<TEntity>().HasQueryFilter(s => s.TenantId == userService.CurrentUserId);
}

原正常代码生成的SQL #

Executed DbCommand (2ms) [Parameters=[@__ef_filter__CurrentUserId_0='b00ffd0d-1fd1-ed11-bef1-f8b54d53dd5f' (Size = 255), @__p_0='0', @__p_1='10'], CommandType='Text', CommandTimeout='60']
      SELECT [s].[ID], [s].[AcademicYear], [s].[Address], [s].[Age], [s].[AuditId], [s].[ClassRoomId], [s].[CourseId], [s].[Email], [s].[Name], [s].[PhoneNumbers], [s].[SoftDeleteId], [s].[StudentType], [s].[SynchronizeId], [s].[TeacherId], [s].[TenantId], [s].[Url]
      FROM [Student] AS [s]
      WHERE [s].[TenantId] = @__ef_filter__CurrentUserId_0
      ORDER BY [s].[Name]
      OFFSET @__p_0 ROWS FETCH NEXT @__p_1 ROWS ONLY

扩展方法代码（有问题的版本） #

public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions options) : base(options) { }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        builder.SetTenantQueryFilter<ClassRoom>();
        builder.SetTenantQueryFilter<Course>();
        builder.SetTenantQueryFilter<Demo>();
        builder.SetTenantQueryFilter<Student>();
        builder.SetTenantQueryFilter<Teacher>();
    }
}

public static class DbExtension
{
    private static readonly IUserService UserService = DbContextExtension.ServiceCollection.CheckService<IUserService>();

    public static void SetTenantQueryFilter<TEntity>(this ModelBuilder builder) where TEntity : class, IUserIsolation
        => builder.Entity<TEntity>().HasQueryFilter(s => s.TenantId == UserService.CurrentUserId);
}

有问题的扩展方法生成的SQL #

Executed DbCommand (1ms) [Parameters=[@__p_0='0', @__p_1='10'], CommandType='Text', CommandTimeout='60']
      SELECT [s].[ID], [s].[AcademicYear], [s].[Address], [s].[Age], [s].[AuditId], [s].[ClassRoomId], [s].[CourseId], [s].[Email], [s].[Name], [s].[PhoneNumbers], [s].[SoftDeleteId], [s].[StudentType], [s].[SynchronizeId], [s].[TeacherId], [s].[TenantId], [s].[Url]
      FROM [Student] AS [s]
      WHERE [s].[TenantId] = N'b00ffd0d-1fd1-ed11-bef1-f8b54d53dd5f'
      ORDER BY [s].[Name]
      OFFSET @__p_0 ROWS FETCH NEXT @__p_1 ROWS ONLY

问题根源 #

扩展方法中使用了静态只读的IUserService实例，OnModelCreating只会在EF Core模型构建时执行一次，此时会直接获取当时的CurrentUserId值并将其硬编码到查询过滤器表达式中，后续切换租户时，过滤器表达式已经固化，不会再重新获取新的租户ID。

而原正常代码中，userService是ApplicationDbContext的实例字段，每次创建DbContext实例时都会关联对应的IUserService，查询过滤器表达式捕获这个实例字段后，EF Core会将其识别为需要动态求值的成员，每次查询时都会实时获取CurrentUserId的最新值，因此能正常切换租户。

解决方案 #

方案1：扩展方法接收IUserService实例作为参数 #

将DbContext中注入的IUserService实例传入扩展方法，确保过滤器捕获的是当前DbContext关联的服务实例：

public class ApplicationDbContext : DbContext
{
    private readonly IUserService _userService;

    // 推荐通过构造函数注入IUserService，避免直接操作ServiceCollection
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options, IUserService userService) 
        : base(options)
    {
        _userService = userService;
    }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        builder.SetTenantQueryFilter<ClassRoom>(_userService);
        builder.SetTenantQueryFilter<Course>(_userService);
        builder.SetTenantQueryFilter<Demo>(_userService);
        builder.SetTenantQueryFilter<Student>(_userService);
        builder.SetTenantQueryFilter<Teacher>(_userService);
    }
}

public static class DbExtension
{
    public static void SetTenantQueryFilter<TEntity>(this ModelBuilder builder, IUserService userService) 
        where TEntity : class, IUserIsolation
    {
        builder.Entity<TEntity>().HasQueryFilter(s => s.TenantId == userService.CurrentUserId);
    }
}

方案2：从DbContext动态获取IUserService #

如果不想在OnModelCreating中传递服务实例，可以让扩展方法通过DbContext的GetService方法动态获取服务：

public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) 
        : base(options) { }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        builder.SetTenantQueryFilter<ClassRoom>(this);
        builder.SetTenantQueryFilter<Course>(this);
        builder.SetTenantQueryFilter<Demo>(this);
        builder.SetTenantQueryFilter<Student>(this);
        builder.SetTenantQueryFilter<Teacher>(this);
    }
}

public static class DbExtension
{
    public static void SetTenantQueryFilter<TEntity>(this ModelBuilder builder, DbContext dbContext) 
        where TEntity : class, IUserIsolation
    {
        var userService = dbContext.GetService<IUserService>();
        builder.Entity<TEntity>().HasQueryFilter(s => s.TenantId == userService.CurrentUserId);
    }
}

方案效果 #

两种方案都能让EF Core识别到userService.CurrentUserId是需要动态求值的成员，每次执行查询时都会获取最新的租户ID，生成的SQL会将其作为参数传递，而非硬编码固定值，切换租户后过滤器会自动生效。

内容的提问来源于stack exchange，提问作者Kannan Chithamabaranathan