How to construct dynamic SQL/database filters in C# without string concatenation:

// Building: p => p.Price > 100 && p.Category == "Electronics"
var parameter = Expression.Parameter(typeof(Product), "p");
var priceProp = Expression.Property(parameter, "Price");
var priceVal = Expression.Constant(100m);
var priceComparison = Expression.GreaterThan(priceProp, priceVal);

var lambda = Expression.Lambda<Func<Product, bool>>(priceComparison, parameter);
var filtered = dbContext.Products.Where(lambda).ToList();

Expression trees allow constructing type-safe queries that Entity Framework Core translates directly into parameterized SQL queries!

Compiling expression trees (lambda.Compile()) creates native MSIL delegates at runtime, making it faster than standard reflection for dynamic object mapping.

Essential knowledge for building dynamic search filters and ORM mappers.