c# - 如何从 Expression<Func<T>> 构建 Expression<Func<T,bool>>

Question

有没有办法构建Expression<Func<T,bool>>来自 Expression<Func<T>> ？

例如类

public class MyClass
{
    public int Prop1{get;set;}
    public int Prop2{get;set;}
    public int Prop3{get;set;}
}

如果Expression<Func<T>>是() => new MyClass{Prop2 = 5}那么结果应该是x => x.Prop2 == 5

如果Expression<Func<T>>是() => new MyClass{Prop1 = 1, Prop3 = 3}那么结果应该是x => x.Prop1 == 1 && x.Prop3 == 3

换句话说，是否可以在运行时创建具有任意数量条件的函数？

Answer 1

像这样:

static Expression<Func<T,bool>> Munge<T>(Expression<Func<T>> selector)
{
    var memberInit = selector.Body as MemberInitExpression;
    if (memberInit == null)
        throw new InvalidOperationException("MemberInitExpression is expected");
    var p = Expression.Parameter(typeof(T), "x");

    Expression body = null;
    foreach (MemberAssignment binding in memberInit.Bindings)
    {
        var comparer = Expression.Equal(
            Expression.MakeMemberAccess(p, binding.Member),
            binding.Expression);
        body = body == null ? comparer : Expression.AndAlso(body, comparer);
    }
    if (body == null) body = Expression.Constant(true);

    return Expression.Lambda<Func<T, bool>>(body, p);
}