Question

我创建了一个表达式来过滤Linq语句：

Expression<Func<Driver, bool>> expression = null;

根据操作参数的值进行定义：

switch (driver_type)
{
    case "all": // remove any filters related to `driver_type`
        expression = d => true;
        break;
    case "licensed":
        expression = d => !(new string[] { "A", "B" }).Contains(d.DriverType);
        break;
    case "unlicensed":
        expression = d => d.DriverType == "D";
        break;
    default:
        expression = d => !(new string[] { "A", "B" }).Contains(d.DriverType);
        break;
}

然后将其用于过滤Linq查询：

drivers = await (
    from driver in _context.Drivers
    where
        (driver.Active == true)
        && expression <-- invalid
    orderby driver.LastName, driver.FirstName
    select driver
).ToListAsync();

正确的语法是什么？

顺便说一句，default开关选项是否可以使用由licensed选项生成的表达式？

Answer 1

您需要将其作为lambda传递。为了使其更具可读性，您可以将整个表达式更改为使用lambda。

drivers = await _context.Drivers
    .Where(driver => driver.Active)
    .Where(expression)
    .OrderBy(driver => driver.LastName)
    .ThenBy(driver => driver.FirstName)
    .ToListAsync();

在Linq查询中使用表达式的正确语法是什么？

1 个答案: