# Alter Queryable Services

Security filtering and tenant isolation for dynamic queries.

## Overview

`IAlterQueryableService<TSource, TDestination>` provides middleware to modify queries before execution. This enables:

- ✅ **Security filters** - Apply user-specific or role-based filters
- ✅ **Tenant isolation** - Multi-tenant data separation
- ✅ **Soft delete filtering** - Automatically exclude deleted records
- ✅ **Row-level security** - Restrict access based on ownership
- ✅ **Data privacy** - Filter sensitive data per user permissions
- ✅ **Audit filters** - Automatically track query context

## IAlterQueryableService Interface

```csharp
public interface IAlterQueryableService<TSource, TDestination>
{
    IQueryable<TSource> AlterQueryable(IQueryable<TSource> queryable);
}
```

**Execution Order:**
1. Get base queryable from provider
2. Apply all registered `IAlterQueryableService` instances (in order)
3. Apply dynamic query filters
4. Execute query

## Tenant Isolation

### Basic Tenant Filter

```csharp
public interface ITenantEntity
{
    int TenantId { get; }
}

public class Product : ITenantEntity
{
    public int Id { get; set; }
    public string Name { get; set; } = string.Empty;
    public int TenantId { get; set; }
}

public class TenantFilterService : IAlterQueryableService<Product, ProductDto>
{
    private readonly ITenantContext _tenantContext;

    public TenantFilterService(ITenantContext tenantContext)
    {
        _tenantContext = tenantContext;
    }

    public IQueryable<Product> AlterQueryable(IQueryable<Product> queryable)
    {
        var tenantId = _tenantContext.TenantId;
        return queryable.Where(p => p.TenantId == tenantId);
    }
}
```

### Registration

```csharp
builder.Services.AddDynamicQuery<Product, ProductDto>()
    .AddDynamicQueryWithProvider<Product, ProductQueryableProvider>()
    .AddAlterQueryable<Product, ProductDto, TenantFilterService>();
```

### Generic Tenant Filter

```csharp
public class TenantFilterService<TSource, TDestination> : IAlterQueryableService<TSource, TDestination>
    where TSource : ITenantEntity
{
    private readonly ITenantContext _tenantContext;

    public TenantFilterService(ITenantContext tenantContext)
    {
        _tenantContext = tenantContext;
    }

    public IQueryable<TSource> AlterQueryable(IQueryable<TSource> queryable)
    {
        var tenantId = _tenantContext.TenantId;
        return queryable.Where(e => e.TenantId == tenantId);
    }
}

// Register for multiple entities
builder.Services.AddAlterQueryable<Product, ProductDto, TenantFilterService<Product, ProductDto>>();
builder.Services.AddAlterQueryable<Order, OrderDto, TenantFilterService<Order, OrderDto>>();
```

## User-Specific Filtering

### Current User's Data

```csharp
public class UserOrderFilterService : IAlterQueryableService<Order, OrderDto>
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public UserOrderFilterService(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public IQueryable<Order> AlterQueryable(IQueryable<Order> queryable)
    {
        var userId = _httpContextAccessor.HttpContext?.User
            .FindFirst(ClaimTypes.NameIdentifier)?.Value;

        if (string.IsNullOrEmpty(userId))
        {
            // No authenticated user - return empty results
            return queryable.Where(o => false);
        }

        // Admins see all orders
        if (_httpContextAccessor.HttpContext.User.IsInRole("Admin"))
        {
            return queryable;
        }

        // Regular users see only their orders
        return queryable.Where(o => o.UserId == userId);
    }
}
```

### Team/Organization Access

```csharp
public class TeamDocumentFilterService : IAlterQueryableService<Document, DocumentDto>
{
    private readonly IHttpContextAccessor _httpContextAccessor;
    private readonly IUserService _userService;

    public TeamDocumentFilterService(
        IHttpContextAccessor httpContextAccessor,
        IUserService userService)
    {
        _httpContextAccessor = httpContextAccessor;
        _userService = userService;
    }

    public IQueryable<Document> AlterQueryable(IQueryable<Document> queryable)
    {
        var userId = _httpContextAccessor.HttpContext?.User
            .FindFirst(ClaimTypes.NameIdentifier)?.Value;

        if (string.IsNullOrEmpty(userId))
            return queryable.Where(d => false);

        var userTeamIds = _userService.GetUserTeamIds(userId);

        return queryable.Where(d =>
            d.OwnerId == userId ||                    // User owns document
            userTeamIds.Contains(d.TeamId) ||         // User's team has access
            d.IsPublic);                              // Public documents
    }
}
```

## Soft Delete Filtering

### Automatic Soft Delete Filter

```csharp
public interface ISoftDeletable
{
    DateTime? DeletedAt { get; }
}

public class SoftDeleteFilterService<TSource, TDestination> : IAlterQueryableService<TSource, TDestination>
    where TSource : ISoftDeletable
{
    public IQueryable<TSource> AlterQueryable(IQueryable<TSource> queryable)
    {
        return queryable.Where(e => e.DeletedAt == null);
    }
}

// Registration
builder.Services.AddAlterQueryable<Product, ProductDto, SoftDeleteFilterService<Product, ProductDto>>();
```

### Soft Delete with Admin Override

```csharp
public class SoftDeleteFilterService<TSource, TDestination> : IAlterQueryableService<TSource, TDestination>
    where TSource : ISoftDeletable
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public SoftDeleteFilterService(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public IQueryable<TSource> AlterQueryable(IQueryable<TSource> queryable)
    {
        // Admins see soft-deleted items
        if (_httpContextAccessor.HttpContext?.User.IsInRole("Admin") == true)
        {
            return queryable;
        }

        // Regular users don't see soft-deleted items
        return queryable.Where(e => e.DeletedAt == null);
    }
}
```

## Row-Level Security

### Hierarchical Access

```csharp
public class HierarchicalAccessFilterService : IAlterQueryableService<Employee, EmployeeDto>
{
    private readonly IHttpContextAccessor _httpContextAccessor;
    private readonly IEmployeeRepository _employeeRepository;

    public HierarchicalAccessFilterService(
        IHttpContextAccessor httpContextAccessor,
        IEmployeeRepository employeeRepository)
    {
        _httpContextAccessor = httpContextAccessor;
        _employeeRepository = employeeRepository;
    }

    public IQueryable<Employee> AlterQueryable(IQueryable<Employee> queryable)
    {
        var currentUserId = _httpContextAccessor.HttpContext?.User
            .FindFirst(ClaimTypes.NameIdentifier)?.Value;

        if (string.IsNullOrEmpty(currentUserId))
            return queryable.Where(e => false);

        // Get all subordinate IDs for the current user
        var subordinateIds = _employeeRepository.GetSubordinateIds(currentUserId);

        // User can see themselves and their subordinates
        return queryable.Where(e =>
            e.UserId == currentUserId ||
            subordinateIds.Contains(e.Id));
    }
}
```

## Data Privacy Filters

### Privacy Level Filtering

```csharp
public class PrivacyFilterService : IAlterQueryableService<UserProfile, UserProfileDto>
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public PrivacyFilterService(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public IQueryable<UserProfile> AlterQueryable(IQueryable<UserProfile> queryable)
    {
        var currentUserId = _httpContextAccessor.HttpContext?.User
            .FindFirst(ClaimTypes.NameIdentifier)?.Value;

        if (string.IsNullOrEmpty(currentUserId))
        {
            // Unauthenticated users see only public profiles
            return queryable.Where(p => p.PrivacyLevel == PrivacyLevel.Public);
        }

        // Authenticated users see public and friends-only profiles
        return queryable.Where(p =>
            p.PrivacyLevel == PrivacyLevel.Public ||
            (p.PrivacyLevel == PrivacyLevel.FriendsOnly && p.UserId == currentUserId) ||
            p.UserId == currentUserId); // Users always see their own profile
    }
}
```

## Multiple Filters

### Chaining Multiple Services

```csharp
// Service 1: Tenant isolation
public class TenantFilterService : IAlterQueryableService<Product, ProductDto>
{
    private readonly ITenantContext _tenantContext;

    public IQueryable<Product> AlterQueryable(IQueryable<Product> queryable)
    {
        return queryable.Where(p => p.TenantId == _tenantContext.TenantId);
    }
}

// Service 2: Soft delete filtering
public class SoftDeleteFilterService : IAlterQueryableService<Product, ProductDto>
{
    public IQueryable<Product> AlterQueryable(IQueryable<Product> queryable)
    {
        return queryable.Where(p => p.DeletedAt == null);
    }
}

// Service 3: Active items only
public class ActiveFilterService : IAlterQueryableService<Product, ProductDto>
{
    public IQueryable<Product> AlterQueryable(IQueryable<Product> queryable)
    {
        return queryable.Where(p => p.IsActive);
    }
}

// Registration - executed in order
builder.Services.AddDynamicQuery<Product, ProductDto>()
    .AddDynamicQueryWithProvider<Product, ProductQueryableProvider>()
    .AddAlterQueryable<Product, ProductDto, TenantFilterService>()
    .AddAlterQueryable<Product, ProductDto, SoftDeleteFilterService>()
    .AddAlterQueryable<Product, ProductDto, ActiveFilterService>();

// Resulting query:
// FROM Products
// WHERE TenantId = @tenantId
//   AND DeletedAt IS NULL
//   AND IsActive = true
//   AND [user-specified filters]
```

## Conditional Filters

### Feature Flag Filter

```csharp
public class FeatureFlagFilterService : IAlterQueryableService<Product, ProductDto>
{
    private readonly IFeatureFlagService _featureFlagService;

    public FeatureFlagFilterService(IFeatureFlagService featureFlagService)
    {
        _featureFlagService = featureFlagService;
    }

    public IQueryable<Product> AlterQueryable(IQueryable<Product> queryable)
    {
        // If beta features are disabled, hide beta products
        if (!_featureFlagService.IsEnabled("BetaProducts"))
        {
            return queryable.Where(p => !p.IsBeta);
        }

        return queryable;
    }
}
```

### Environment-Specific Filter

```csharp
public class EnvironmentFilterService : IAlterQueryableService<Product, ProductDto>
{
    private readonly IWebHostEnvironment _environment;

    public EnvironmentFilterService(IWebHostEnvironment environment)
    {
        _environment = environment;
    }

    public IQueryable<Product> AlterQueryable(IQueryable<Product> queryable)
    {
        // In production, hide test products
        if (_environment.IsProduction())
        {
            return queryable.Where(p => !p.IsTestData);
        }

        return queryable;
    }
}
```

## Testing Alter Queryable Services

### Unit Tests

```csharp
public class TenantFilterServiceTests
{
    private readonly Mock<ITenantContext> _mockTenantContext;
    private readonly TenantFilterService _service;

    public TenantFilterServiceTests()
    {
        _mockTenantContext = new Mock<ITenantContext>();
        _service = new TenantFilterService(_mockTenantContext.Object);
    }

    [Fact]
    public void AlterQueryable_FiltersByTenantId()
    {
        // Arrange
        _mockTenantContext.Setup(c => c.TenantId).Returns(123);

        var products = new List<Product>
        {
            new() { Id = 1, Name = "Product 1", TenantId = 123 },
            new() { Id = 2, Name = "Product 2", TenantId = 456 },
            new() { Id = 3, Name = "Product 3", TenantId = 123 }
        }.AsQueryable();

        // Act
        var result = _service.AlterQueryable(products).ToList();

        // Assert
        Assert.Equal(2, result.Count);
        Assert.All(result, p => Assert.Equal(123, p.TenantId));
    }
}
```

## Performance Considerations

### Indexing for Filters

```csharp
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Product>(entity =>
    {
        // Index columns used in AlterQueryableService
        entity.HasIndex(e => e.TenantId);
        entity.HasIndex(e => e.DeletedAt);
        entity.HasIndex(e => e.IsActive);

        // Composite index for multiple filters
        entity.HasIndex(e => new { e.TenantId, e.DeletedAt, e.IsActive });
    });
}
```

### Avoid N+1 Queries

```csharp
// ❌ Bad - Multiple database calls
public IQueryable<Document> AlterQueryable(IQueryable<Document> queryable)
{
    var userId = GetCurrentUserId();

    foreach (var teamId in GetUserTeamIds(userId)) // Multiple DB calls
    {
        queryable = queryable.Where(d => d.TeamId == teamId);
    }

    return queryable;
}

// ✅ Good - Single database call
public IQueryable<Document> AlterQueryable(IQueryable<Document> queryable)
{
    var userId = GetCurrentUserId();
    var teamIds = GetUserTeamIds(userId).ToList(); // Materialize once

    return queryable.Where(d => teamIds.Contains(d.TeamId));
}
```

## Best Practices

### ✅ DO

- Apply security filters in IAlterQueryableService
- Index columns used in alter queryable filters
- Test alter queryable services independently
- Use generic implementations for common patterns
- Chain multiple services for separation of concerns
- Return queryable.Where(x => false) for unauthorized access

### ❌ DON'T

- Don't perform synchronous I/O (ToList, Count, etc.)
- Don't skip security filters for "trusted" users
- Don't modify the queryable parameter directly
- Don't throw exceptions for access denied (return empty results)
- Don't perform complex joins in alter queryable
- Don't bypass filters based on user input

## Common Patterns

### Pattern: Base Security Service

```csharp
public abstract class SecurityFilterService<TSource, TDestination> : IAlterQueryableService<TSource, TDestination>
    where TSource : ISecureEntity
{
    protected readonly IHttpContextAccessor _httpContextAccessor;

    protected SecurityFilterService(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public IQueryable<TSource> AlterQueryable(IQueryable<TSource> queryable)
    {
        var user = _httpContextAccessor.HttpContext?.User;

        if (user == null || !user.Identity.IsAuthenticated)
            return queryable.Where(e => false);

        if (user.IsInRole("Admin"))
            return queryable;

        return ApplyUserFilters(queryable, user);
    }

    protected abstract IQueryable<TSource> ApplyUserFilters(IQueryable<TSource> queryable, ClaimsPrincipal user);
}

// Usage
public class ProductSecurityFilterService : SecurityFilterService<Product, ProductDto>
{
    public ProductSecurityFilterService(IHttpContextAccessor httpContextAccessor)
        : base(httpContextAccessor)
    {
    }

    protected override IQueryable<Product> ApplyUserFilters(IQueryable<Product> queryable, ClaimsPrincipal user)
    {
        var userId = user.FindFirst(ClaimTypes.NameIdentifier)?.Value;
        return queryable.Where(p => p.CreatedBy == userId);
    }
}
```

## See Also

- [Dynamic Queries Overview](README.md)
- [Queryable Providers](queryable-providers.md)
- [Interceptors](interceptors.md)
- [Query Authorization](../queries/query-authorization.md)
- [Best Practices: Security](../../best-practices/security.md)