Compiled Queries in EF Core

What are Compiled Queries?

Compiled queries are pre-compiled LINQ queries that improve performance by caching the query translation. They’re useful for frequently executed queries.

Basic Usage

private static readonly Func<ApplicationDbContext, int, IEnumerable<Product>> _getProductsByCategory =
    EF.CompileQuery((ApplicationDbContext context, int categoryId) =>
        context.Products.Where(p => p.CategoryId == categoryId));

// Usage
var products = _getProductsByCategory(context, 5).ToList();

Async Compiled Queries

private static readonly Func<ApplicationDbContext, int, IAsyncEnumerable<Product>> _getProductsByCategoryAsync =
    EF.CompileAsyncQuery((ApplicationDbContext context, int categoryId) =>
        context.Products.Where(p => p.CategoryId == categoryId));

// Usage
await foreach (var product in _getProductsByCategoryAsync(context, 5))
{
    Console.WriteLine(product.Name);
}

Multiple Parameters

private static readonly Func<ApplicationDbContext, int, decimal, IEnumerable<Product>> _getProducts =
    EF.CompileQuery((ApplicationDbContext context, int categoryId, decimal minPrice) =>
        context.Products
            .Where(p => p.CategoryId == categoryId && p.Price >= minPrice)
            .OrderBy(p => p.Name));

With Includes

private static readonly Func<ApplicationDbContext, int, Product> _getProductWithCategory =
    EF.CompileQuery((ApplicationDbContext context, int productId) =>
        context.Products
            .Include(p => p.Category)
            .FirstOrDefault(p => p.Id == productId));

Performance Benefits

// First call: Compiles and caches
var products1 = _getProductsByCategory(context, 5);

// Subsequent calls: Uses cached compilation
var products2 = _getProductsByCategory(context, 10); // Faster

Summary

Compiled queries in EF Core cache query translation for better performance. Use EF.CompileQuery for sync and EF.CompileAsyncQuery for async queries. Best for frequently executed queries.