可以修改此函数来处理多个属性比较吗？

Question

供参考，这是原始问题：DynamicWhere for List

这允许您执行此操作：

var people = new[] {
            new { FirstName = "John", LastName = "Smith" },
            new { FirstName = "John", LastName = "Smith" },
            new { FirstName = "John", LastName = "Noakes" },
            new { FirstName = "Linda", LastName = "Smith" },
            new { FirstName = "Richard", LastName = "Smith" },
            new { FirstName = "Richard", LastName = "Littlejohn" },
        }.ToList();

var filtered = people.Filter("LastName", "Smith");

但是如果您想要匹配多个属性怎么办？例如，如果我想过滤所有名字=约翰和姓氏=史密斯的人

Pseduocode 只是为了给出这个想法，我确信有一种更优雅的方式来编码：

var filtered = people.Filter(new [] {Column="FirstName", Value = "John"}, {Column="LastName", Value="Smith"});

也很好奇这是否可以轻松地适应处理属性的任何类型（即对象而不是像示例那样总是字符串）。我没有太多使用这些表达式树，我感谢您提供的任何帮助。

Answer 1

您可以使用此处的

AndAlso

扩展来组合多个表达式。然后将您的过滤方法更改为：

public static List<T> Filter<T>(this List<T> source, params (string columnName, string compValue)[] filters)
{
    Expression<Func<T, bool>> exp = null;
    
    foreach (var filter in filters)
    {
        ParameterExpression parameter = Expression.Parameter(typeof(T), "x");
        Expression property = Expression.Property(parameter, filter.columnName);
        Expression constant = Expression.Constant(filter.compValue);
        Expression equality = Expression.Equal(property, constant);
        Expression<Func<T, bool>> predicate = Expression.Lambda<Func<T, bool>>(equality, parameter);
        
        exp = exp is null ? predicate : exp.AndAlso(predicate);
    }

    Func<T, bool> compiled = exp.Compile();
    return source.Where(compiled).ToList();
}

并这样称呼它：

var results = people.Filter(("FirstName", "John"), ("LastName", "Smith"));

这篇文章写得很快，因此您可能不喜欢使用元组列表。

Answer 2

var people = new[] {
        new { FirstName = "John", LastName = "Smith" },
        new { FirstName = "John", LastName = "Smith" },
        new { FirstName = "John", LastName = "Noakes" },
        new { FirstName = "Linda", LastName = "Smith" },
        new { FirstName = "Richard", LastName = "Smith" },
        new { FirstName = "Richard", LastName = "Littlejohn" },
    }.ToList();
   var TestData=people.Where(o=>o.FirstName=="John" && o.LastName == "Smith" ).ToList();

您将在“TestData”上获得结果列表