Query Pattern¶

Query Pattern, veri okuma işlemlerini temsil eden bir pattern’dır. MediatR’da query’ler de IRequest<T> interface’ini implemente eder.

Query Özellikleri¶

Read-Only: Query’ler sadece veri okumalıdır
Tek Sorumluluk: Her query tek bir veri seti dönmelidir
Performans: Query’ler optimize edilmiş olmalıdır
Caching: Mümkünse caching kullanılmalıdır

Query Örnekleri¶

Basit Query¶

public class GetProductByIdQuery : IRequest<ProductDto>
{
    public int Id { get; set; }
}

public class GetProductByIdQueryHandler : IRequestHandler<GetProductByIdQuery, ProductDto>
{
    private readonly IProductRepository _repository;

    public GetProductByIdQueryHandler(IProductRepository repository)
    {
        _repository = repository;
    }

    public async Task<ProductDto> Handle(GetProductByIdQuery request, CancellationToken cancellationToken)
    {
        var product = await _repository.GetByIdAsync(request.Id);
        return new ProductDto
        {
            Id = product.Id,
            Name = product.Name,
            Price = product.Price
        };
    }
}

Complex Query¶

public class GetProductsQuery : IRequest<PagedList<ProductDto>>
{
    public string SearchTerm { get; set; }
    public int PageNumber { get; set; } = 1;
    public int PageSize { get; set; } = 10;
    public string SortBy { get; set; }
    public bool SortDescending { get; set; }
}

public class GetProductsQueryHandler : IRequestHandler<GetProductsQuery, PagedList<ProductDto>>
{
    private readonly IProductRepository _repository;

    public GetProductsQueryHandler(IProductRepository repository)
    {
        _repository = repository;
    }

    public async Task<PagedList<ProductDto>> Handle(GetProductsQuery request, CancellationToken cancellationToken)
    {
        var query = _repository.GetAll();

        if (!string.IsNullOrWhiteSpace(request.SearchTerm))
        {
            query = query.Where(p => p.Name.Contains(request.SearchTerm));
        }

        query = request.SortDescending
            ? query.OrderByDescending(p => EF.Property<object>(p, request.SortBy))
            : query.OrderBy(p => EF.Property<object>(p, request.SortBy));

        var totalCount = await query.CountAsync();
        var items = await query
            .Skip((request.PageNumber - 1) * request.PageSize)
            .Take(request.PageSize)
            .Select(p => new ProductDto
            {
                Id = p.Id,
                Name = p.Name,
                Price = p.Price
            })
            .ToListAsync();

        return new PagedList<ProductDto>(items, totalCount, request.PageNumber, request.PageSize);
    }
}

Query Best Practices¶

Query Optimization - Select sadece ihtiyaç duyulan alanları - Include’ları dikkatli kullanın - Index’leri doğru kullanın
Query Handler Organization - Repository pattern kullanın - DTO’ları kullanın - Mapping işlemlerini otomatize edin
Caching - Query sonuçlarını cache’leyin - Cache invalidation stratejisi belirleyin - Distributed cache kullanın
Testing - Query’leri unit test edin - Integration testler yazın - Performance testleri yapın

Query Pipeline¶

Query’ler pipeline üzerinden geçer:

Caching
Validation
Authorization
Logging
Handler

public class QueryPipelineBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    private readonly ICacheService _cache;

    public QueryPipelineBehavior(ICacheService cache)
    {
        _cache = cache;
    }

    public async Task<TResponse> Handle(
        TRequest request,
        RequestHandlerDelegate<TResponse> next,
        CancellationToken cancellationToken)
    {
        var cacheKey = $"{typeof(TRequest).Name}-{request.GetHashCode()}";

        var cachedResponse = await _cache.GetAsync<TResponse>(cacheKey);
        if (cachedResponse != null)
        {
            return cachedResponse;
        }

        var response = await next();
        await _cache.SetAsync(cacheKey, response);

        return response;
    }
}