c# - 获取作为 lambda 表达式传递的参数的 PropertyInfo

Question

比如我有一个类:

public class Person
{
  public int Id;
  public string Name, Address;
}

并且我想调用一个方法来根据 Id 更新此类中的信息:

update(myId, myPerson => myPerson.Name = "abc");

解释:这个方法会从数据库中查询并得到Person实体给定一个myId，然后它设置Name为“abc”，所以它的作用与我所说的相同:

update(myId, myPerson => myPerson.Address = "my address");

这可能吗？如果是怎么办？

Answer 1

我不会使用 PropertyInfo，就像 Reed Copsey 在他的回答中所说的那样，但仅供引用，您可以提取 PropertyInfo的表达式:

public PropertyInfo GetPropertyFromExpression<T>(Expression<Func<T, object>> GetPropertyLambda)
{
    MemberExpression Exp = null;

    //this line is necessary, because sometimes the expression comes in as Convert(originalexpression)
    if (GetPropertyLambda.Body is UnaryExpression)
    {
        var UnExp = (UnaryExpression)GetPropertyLambda.Body;
        if (UnExp.Operand is MemberExpression)
        {
            Exp = (MemberExpression)UnExp.Operand;
        }
        else
            throw new ArgumentException();
    }
    else if (GetPropertyLambda.Body is MemberExpression)
    {
        Exp = (MemberExpression)GetPropertyLambda.Body;
    }
    else
    {
        throw new ArgumentException();
    }

    return (PropertyInfo)Exp.Member;
}

---

对于像 MyPerson.PersonData.PersonID 这样的复合表达式，您可以获取子表达式，直到它们不再是 MemberExpressions。

public PropertyInfo GetPropertyFromExpression<T>(Expression<Func<T, object>> GetPropertyLambda)
{
    //same body of above method without the return line.
    //....
    //....
    //....

    var Result = (PropertyInfo)Exp.Member;

    var Sub = Exp.Expression;

    while (Sub is MemberExpression)
    {
        Exp = (MemberExpression)Sub;
        Result = (PropertyInfo)Exp.Member;
        Sub = Exp.Expression;
    }

    return Result;
    //beware, this will return the last property in the expression.
    //when using GetValue and SetValue, the object needed will not be
    //the first object in the expression, but the one prior to the last.
    //To use those methods with the first object, you will need to keep
    //track of all properties in all member expressions above and do
    //some recursive Get/Set following the sequence of the expression.
}