c# - 如何从 lambda 表达式获取值？

Question

我有这门课:

public class CustomerFilter
{
    public int Id { get; set; }
    public int Name { get; set; }
}

它的用法如下:

public class Search
{
    private Expression<Func<CustomerFilter, bool>> customerfilter;

    public Expression<Func<CustomerFilter, bool>> CustomerFilter
    {
        set { customerfilter = value; }
    }
}

var search = new Search();
search.CustomerFilter = (x => x.Id == 1);

在搜索类中，如何在不使用 ExpressionVisitor 的情况下获取属性值？像这样的东西:

var customerId = customerFilter.Id; //Or something similar

Answer 1

不太明白为什么需要它。但是，你可以这样做:

public class Search
{
    private Expression<Func<CustomerFilter, bool>> customerfilter;

    public Expression<Func<CustomerFilter, bool>> CustomerFilter
    {
        set { customerfilter = value; }
    }

    public object GetValue(CustomerFilter filter)
    {
        var property = (customerfilter.Body as BinaryExpression).Left;
        var lambda =Expression.Lambda(property, customerfilter.Parameters.First());
        return lambda.Compile().DynamicInvoke(filter);
    }
}

这样的用法:

var search = new Search();
search.CustomerFilter = (x => x.Id == 1);
var filter = new CustomerFilter {Id = 12};
search.GetValue(filter).Dump();

我得到12作为输出