将2个参数Lambda表达式转换为1个参数Lambda表达式(指定一个参数) [英] Converting 2 argument Lambda expression to 1 argument Lambda expression (specifying one argument)

问题描述

我有表情

Expression<Func<Car, Driver, bool>> CanBeDrivenBy = 
    (car, driver) => car.Category == 'B' && driver.Age > 18;

我想得到可以由某些驾驶员驾驶的汽车

and I want to get cars which can be driven by some driver

IQueryable<Cars> cars = ...;
Driver driver = ...;
cars.Where(CanBeDrivenBy);   // Fail, expecting Expression<Func<Car, bool>>

所以我需要将Expression<Func<Car, Driver, bool>>转换为Expression<Func<Car, bool>>(指定驱动程序)

So I need to convert Expression<Func<Car, Driver, bool>> to Expression<Func<Car, bool>> (specify driver)

是的，我可以使用

cars.Where(c => c.Category == 'B' && driver.Age > 18);

但是我需要可以动态更改表达式的解决方案.而且我需要通过表达式(使用实体框架)

but I need solution with expression which can be changed dynamicly. And I need to pass Expression (using entity framework)

推荐答案

此工作

我编写了此函数，通过指定第二个参数来将参数数量从2减少到1.

I wrote this function to reduce number of arguments from 2 to 1 by specifying the second argument.

public static Expression<Func<T1, TResult>> Bind2nd<T1, T2, TResult>(Expression<Func<T1, T2, TResult>> source, T2 argument)
{
    Expression arg2 = Expression.Constant(argument, typeof(T2));
    var arg1 = Expression.Parameter(typeof(T1));
    return Expression.Lambda<Func<T1, TResult>>(Expression.Invoke(source, arg1, arg2), arg1);
}

用法:

IQueryable<Car> cars = ...;
Driver driver = ...;
cars.Where(Bind2nd(CanBeDrivenBy, driver));

arg1是通话之间的临时存储.

arg1 is temporary storage between calls.

有任何等效的系统功能吗?

Is there any system equivalent function?

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