我昨天在这里问了一个关于从匿名对象读取属性并将它们写入类的私有字段的问题。问题解决了。这是一个简短的故事:
我有一些 json 格式的数据。我将它们反序列化为ExpandoObject
,并将它们作为IDictionary<string, object>
方法传递。它工作正常,除了Int32
属性。似乎他们变成了Int64
,在哪里?我不知道。
又是这个方法:
private Func<IDictionary<string, object>, dynamic> MakeCreator(
Type type, Expression ctor,
IEnumerable<PropertyToFieldMapper> maps) {
var list = new List<Expression>();
var vList = new List<ParameterExpression>();
// creating new target
var targetVariable = Expression.Variable(type, "targetVariable");
vList.Add(targetVariable);
list.Add(Expression.Assign(targetVariable, Expression.Convert(ctor, type)));
// accessing source
var sourceType = typeof(IDictionary<string, object>);
var sourceParameter = Expression.Parameter(sourceType, "sourceParameter");
// calling source ContainsKey(string) method
var containsKeyMethodInfo = sourceType.GetMethod("ContainsKey", new[] { typeof(string) });
var accessSourceIndexerProp = sourceType.GetProperty("Item");
var accessSourceIndexerInfo = accessSourceIndexerProp.GetGetMethod();
// itrate over writers and add their Call to block
var containsKeyMethodArgument = Expression.Variable(typeof(string), "containsKeyMethodArgument");
vList.Add(containsKeyMethodArgument);
foreach (var map in maps) {
list.Add(Expression.Assign(containsKeyMethodArgument, Expression.Constant(map.Property.Name)));
var containsKeyMethodCall = Expression.Call(sourceParameter, containsKeyMethodInfo,
new Expression[] { containsKeyMethodArgument });
// creating writer
var sourceValue = Expression.Call(sourceParameter, accessSourceIndexerInfo,
new Expression[] { containsKeyMethodArgument });
var setterInfo = map.Field.GetType().GetMethod("SetValue", new[] { typeof(object), typeof(object) });
var setterCall = Expression.Call(Expression.Constant(map.Field), setterInfo,
new Expression[] {
Expression.Convert(targetVariable, typeof(object)),
Expression.Convert(sourceValue, typeof(object))
});
Console.WriteLine(Expression.Lambda(setterCall));
list.Add(Expression.IfThen(containsKeyMethodCall, setterCall));
}
list.Add(targetVariable);
var block = Expression.Block(vList, list);
var lambda = Expression.Lambda<Func<IDictionary<string, object>, dynamic>>(
block, new[] { sourceParameter }
);
return lambda.Compile();
}
如果我们有这个
public class Person {
public int Age { get; set; }
public string Name { get; set; }
}
类,并使用这个对象
var data = new { Name = "Amiry", Age = 20 };
初始化Person
使用上述方法的实例,发生此错误:
“System.Int64”类型的对象无法转换为“System.Int32”类型。
但是,如果我们将Age
属性更改为:
public long Age { get; set; }
每件事看起来都很好,方法也很完美。我完全不明白为什么会发生这种情况。你有什么主意吗?