Bits of .NET

🧠 Expression Trees = Dynamic Queries

Statik sorgular yeterli değil. Expression Trees ile runtime’da dinamik LINQ sorguları oluşturun.

🎯 Expression Tree Örnekleri

// 1. Dinamik WHERE
public static Expression> BuildFilter(
    string propertyName, string operation, object value)
{
    var parameter = Expression.Parameter(typeof(T), "x");
    var property = Expression.Property(parameter, propertyName);
    var constant = Expression.Constant(value);
    
    Expression condition = operation switch
    {
        "Equals" => Expression.Equal(property, constant),
        "GreaterThan" => Expression.GreaterThan(property, constant),
        "LessThan" => Expression.LessThan(property, constant),
        "Contains" => Expression.Call(property, 
            typeof(string).GetMethod("Contains", new[] { typeof(string) }), constant),
        _ => throw new NotSupportedException()
    };
    
    return Expression.Lambda>(condition, parameter);
}

// 2. Dinamik OrderBy
public static IQueryable OrderByDynamic(
    this IQueryable query, string propertyName, bool ascending = true)
{
    var parameter = Expression.Parameter(typeof(T), "x");
    var property = Expression.Property(parameter, propertyName);
    var lambda = Expression.Lambda(property, parameter);
    
    var methodName = ascending ? "OrderBy" : "OrderByDescending";
    var method = typeof(Queryable).GetMethods()
        .First(m => m.Name == methodName && m.GetParameters().Length == 2)
        .MakeGenericMethod(typeof(T), property.Type);
    
    return (IQueryable)method.Invoke(null, new object[] { query, lambda });
}

// 3. Predicate Builder
public static class PredicateBuilder
{
    public static Expression> True() { return f => true; }
    
    public static Expression> And(
        this Expression> expr1,
        Expression> expr2)
    {
        var invokedExpr = Expression.Invoke(expr2, expr1.Parameters);
        return Expression.Lambda>(
            Expression.AndAlso(expr1.Body, invokedExpr),
            expr1.Parameters);
    }
}

✅ Expression Tree Kullanım Alanları

• ✓ Dinamik filtreleme
• ✓ Runtime sorgu oluşturma
• ✓ Özel LINQ provider’lar
• ✓ ORM sorgu optimizasyonu
• ✓ Rule engine implementasyonu