c# - 简化多次使用相同代码的 lambda 表达式

Question

有没有办法可以简化我的 lambda 表达式:

models = _context.something
    .Where(i => i.Amount > 0)
    .Select(o => new somemodel
    {
        one = (o.property.prices.Where(i => i.IsCurrent == true).FirstOrDefault().Value - o.property.prices.Where(i => i.IsCurrent == true).FirstOrDefault().Price).ToString(),
        two = o.property.prices.Where(i => i.IsCurrent == true).FirstOrDefault().Price,
        three = o.property.prices.Where(i => i.IsCurrent == true).FirstOrDefault().Price.ToPriceStr("£"),
        four = o.property.rents.Where(i => i.IsCurrent == true).FirstOrDefault().Rent * 1200 / o.property.prices.Where(i => i.IsCurrent == true).FirstOrDefault().Price,
        five = Convert.ToInt64(o.property.prices.Where(o => o.IsCurrent == true).FirstOrDefault().Value) * o.property.amount,
        six = (Convert.ToInt64(o.property.prices.Where(o => o.IsCurrent == true).FirstOrDefault().Value) * o.property.amount).ToPriceStr("£"),
    })
    .Distinct()
    .ToList();

这只是一个示例，真实的示例多次使用相同类型的代码。它真的很容易出错，就好像我改变它一样，我有很多地方可以做。

代码o.property.prices.Where(i => i.IsCurrent == true).FirstOrDefault() 遍布我的表情。有没有一种方法可以让我一次写入并重复使用它。

Answer 1

这就是查询表达式派上用场的地方，因为它允许 let clauses .

models = (from o in _context.something
    where o.Amount > 0
    let firstCurrentPrice = o.property.prices.Where(i => i.IsCurrent).FirstOrDefault()
    select new some model 
    {
        one = (firstCurrentPrice.Value - firstCurrentPrice.Price).ToString(),
        two = firstCurrentPrice.Price,
        three = firstCurrentPrice.Price.ToPriceStr("£"),
        four = o.property.rents.Where(i => i.IsCurrent == true).FirstOrDefault().Rent * 1200 / firstCurrentPrice.Price,
        five = Convert.ToInt64(firstCurrentPrice.Value) * o.property.amount,
        six = (Convert.ToInt64(firstCurrentPrice.Value) * o.property.amount).ToPriceStr("£"),
    })
    .Distinct()
    .ToList();