与表达式树设置字段值 [英] Set field value with Expression tree
问题描述
我需要创建一个类的所有字段的表达式。
所以我采用的这个帖子以我的需求:
I need to create an expression for all fields in a class. So I've adopted this post to my needs:
public static void Sample()
{
var setters = GetFieldSetterExpressions<Account>();
var myAccount = new Account();
setters["AccounHolder"](myAccount, "Giovanni");
setters["Pin"](myAccount, 123);
}
public static Dictionary<string, Action<T, object>> GetFieldSetterExpressions<T>() where T: class
{
var dic = new Dictionary<string,Action<T,object>>();
var type = typeof(T);
var fields = type.GetFields();
foreach (var fieldInfo in fields)
{
Type fieldType;
if (IsNullableType(fieldInfo.FieldType))
fieldType = Nullable.GetUnderlyingType(fieldInfo.FieldType);
else
fieldType = fieldInfo.FieldType;
ParameterExpression targetExp = Expression.Parameter(type, "target");
ParameterExpression valueExp = Expression.Parameter(fieldType, "value");
MemberExpression fieldExp = Expression.Field(targetExp, fieldInfo);
BinaryExpression assingExp = Expression.Assign(fieldExp, valueExp);
var setter = Expression.Lambda<Action<T, object>>(assingExp, targetExp, valueExp).Compile();
dic.Add(fieldInfo.Name, setter);
}
return dic;
}
我的问题是 Expression.Lambda<作用<吨,对象>>(..)
,因为本场可例如字符串,我得到一个exeption。
我试图intregrate Expression.Convert
在我的片段,但无法弄清楚如何实现它。
My problem is Expression.Lambda<Action<T,object>>(..)
since the field can be for example string, I get an exeption.
I've tried to intregrate Expression.Convert
in my snippet, but couldn't figure out how to implement it.
如何我需要在我的代码转换部分集成的?
How do I need to integrate the conversion part in my code?
推荐答案
表达<作用< T,对象>>
表示第二个参数的类型应为的对象
,而你的代码使用属性类型
。这是应该的:
Expression<Action<T, object>>
means that the second parameter is expected to be of type object
, while your code is using propertyType
. Here is how it should be:
var type = typeof(T);
var fields = type.GetFields();
foreach (var fieldInfo in fields)
{
var targetExp = Expression.Parameter(type, "target");
var valueExp = Expression.Parameter(typeof(object), "value");
var fieldExp = Expression.Field(targetExp, fieldInfo);
var assignExp = Expression.Assign(fieldExp, Expression.Convert(valueExp, fieldExp.Type));
var setter = Expression.Lambda<Action<T, object>>(assignExp, targetExp, valueExp).Compile();
}
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