将一个类的Lambda转换成另一个类的研究

首先是2个相同的类

class ClassA
    {
        public int Id { get; set; }
 
        public string Name { get; set; }
    }
 
    class ClassB
    {
        public int Id { get; set; }
 
        public string Name { get; set; }
    }<br>

然后自定义访问者，将 ParameterExpression全部换成另一个类的

public class MyVisitor<SourceT,DescT> : ExpressionVisitor
    {
        private readonly ParameterExpression DescTParameter = Expression.Parameter(typeof(DescT), "p");
 
        protected override Expression VisitParameter(ParameterExpression node)
        {
            if (node.Type == typeof(SourceT))
            {
                return DescTParameter;
            }
            return base.VisitParameter(node);
        }
 
 
        protected override Expression VisitMember(MemberExpression node)
        {
            if (node.Member.ReflectedType == typeof(SourceT))
            {
                var idExpression = Expression.Property(DescTParameter, node.Member.Name);
                return idExpression;
            }
            return base.VisitMember(node);
        }
 
        public Expression<Func<DescT, bool>> Modify(Expression<Func<SourceT, bool>> expression)
        {
            var result = this.Visit(expression.Body);
            return Expression.Lambda<Func<DescT, bool>>(result, DescTParameter);
        }
 
    }

调用代码如下：

　　　　var classAList = new List<ClassA>
                                 {
                                              new ClassA {Id = 1, Name = "User1"},
                                              new ClassA {Id = 2, Name = "User2"}
                                          };
            Expression<Func<ClassB, bool>> expressionB =
                p => p.Id > 1 && p.Name == "User2";
<br>            MyVisitor<ClassB,ClassA> visitor =new MyVisitor<ClassB, ClassA>();
            var ex = visitor.Modify(expressionB);
            var result = classAList.AsQueryable().Where(ex);
            foreach (var item in result)
            {
                Console.WriteLine(item.Name);
            }