问题描述
我有以下 C# 类
public class Contact
{
public string Firstname { get; set; }
public string Lastname { get; set; }
public List<Phone> Phones { get; set; }
}
public class Phone
{
public string AreaCode { get; set; }
public string PhoneNumber { get; set; }
public bool IsMobile { get; set; }
}
以下是我尝试动态创建的示例表达式。
Expression<Func<Contact,bool>> isMobileExpression = p => p.Phone.First().IsMobile;
我想创建一个类似于上面的表达式,但动态定义“p.Phone.First().IsMobile”表达式而不是对其进行硬编码。 例如:
var paraName = "p => p.Phone.First().IsMobile";
Expression<Func<Contact,bool>> isMobileExpression = p => paraName;
可以这样做吗?提前感谢您的任何帮助。?
解决方法
您可以考虑CSharpScript:
public class Contact
{
public string Firstname { get; set; }
public string Lastname { get; set; }
public List<Phone> Phones { get; set; }
}
public class Phone
{
public string AreaCode { get; set; }
public string PhoneNumber { get; set; }
public bool IsMobile { get; set; }
}
void Main()
{
var code = "return Phones.First().IsMobile;";
var script = CSharpScript.Create<bool>(code,globalsType: typeof(Contact),options: ScriptOptions.Default.WithReferences("System.Linq").WithImports("System.Linq"));
var scriptRunner = script.CreateDelegate();
Console.WriteLine(scriptRunner(new Contact() { Phones = new List<Phone> { new Phone {IsMobile = true }}} ));
Console.WriteLine(scriptRunner(new Contact() { Phones = new List<Phone> { new Phone {IsMobile = false }}} ));
}
更新
如果你想要一个表达式,你可以像这样将 ScriptRunner
委托包装到 Expression.Call()
中:
Expression<Func<Contact,Task<bool>>> GetExpression()
{
var code = "return Phones.First().IsMobile;";
var script = CSharpScript.Create<bool>(code,options: ScriptOptions.Default.WithReferences("System.Linq").WithImports("System.Linq"));
var scriptRunner = script.CreateDelegate();
var p = Expression.Parameter(typeof(Contact));
var mi = scriptRunner.Method;
return Expression.Lambda<Func<Contact,Task<bool>>>(Expression.Call(Expression.Constant(scriptRunner.Target),mi,p,Expression.Constant(CancellationToken.None)),p);
}
然后你就可以按照你认为合适的方式编译和使用它:
void Main()
{
var scriptRunner = GetExpression().Compile();
Console.WriteLine(scriptRunner(new Contact() { Phones = new List<Phone> { new Phone { IsMobile = true } } }));
Console.WriteLine(scriptRunner(new Contact() { Phones = new List<Phone> { new Phone { IsMobile = false } } }));
}
但是我觉得这有点太复杂了。如果您可以直接使用委托,可能会更容易。