如何设置属性选择器的值表达式>
本文关键字:Func 表达式 result 何设置 设置 选择器 属性 | 更新日期: 2023-09-27 18:14:12
我需要关联一个实体属性地址在我的Person类实体与表达式linq在我的FactoryEntities类使用模式工厂的想法,看看这是我所拥有的,我想做的:
Address address = new Address();
address.Country = "Chile";
address.City = "Santiago";
address.ZipCode = "43532";
//Factory instance creation object
//This is idea
Person person = new FactoryEntity<Person>().AssociateWithEntity(p=>p.Address, address);
public class Person: Entity
{
public string Name{ get; set; }
public string LastName{ get; set; }
public Address Address{ get; set; }
}
public class Address: Entity
{
public string Country{ get; set; }
public string City{ get; set; }
public string ZipCode{ get; set; }
}
public class FactoryEntity<TEntity> where TEntity : Entity
{
public void AssociateWithEntity<TProperty>(Expression<Func<TEntity, TProperty>> entityExpression, TProperty newValueEntity) where TProperty : Entity
{
if (instanceEntity == null || instanceEntity.IsTransient())
throw new ArgumentNullException();
/*TODO: Logic the association and validation
How set the newValueEntity into the property of entityExpression (x=>x.Direccion = direccion*/
}
}
这行得通:
下面的帮助方法将getter表达式转换为setter委托。如果你想返回Expression<Action<T,TProperty>>
而不是Action<T,TProperty>
,就不要在最后调用Compile()
方法。
注意:代码来自Ian Mercer的博客:http://blog.abodit.com/2011/09/convert-a-property-getter-to-a-setter/
/// <summary>
/// Convert a lambda expression for a getter into a setter
/// </summary>
public static Action<T, TProperty> GetSetter<T, TProperty>(Expression<Func<T, TProperty>> expression)
{
var memberExpression = (MemberExpression)expression.Body;
var property = (PropertyInfo)memberExpression.Member;
var setMethod = property.GetSetMethod();
var parameterT = Expression.Parameter(typeof(T), "x");
var parameterTProperty = Expression.Parameter(typeof(TProperty), "y");
var newExpression =
Expression.Lambda<Action<T, TProperty>>(
Expression.Call(parameterT, setMethod, parameterTProperty),
parameterT,
parameterTProperty
);
return newExpression.Compile();
}
你可以这样设置属性:
public void AssociateWithEntity<TProperty>(
Expression<Func<TEntity, TProperty>> entityExpression,
TProperty newValueEntity)
where TProperty : Entity
{
if (instanceEntity == null)
throw new ArgumentNullException();
var memberExpression = (MemberExpression)entityExpression.Body;
var property = (PropertyInfo)memberExpression.Member;
property.SetValue(instanceEntity, newValueEntity, null);
}
这只适用于属性,而不适用于字段,尽管添加对字段的支持应该很容易。
但是你得到这个人的代码不起作用。如果您想保留AssociateWithEntity()
的void
返回类型,您可以这样做:
var factory = new FactoryEntity<Person>();
factory.AssociateWithEntity(p => p.Address, address);
Person person = factory.InstanceEntity;
另一个选项是流畅接口:
Person person = new FactoryEntity<Person>()
.AssociateWithEntity(p => p.Address, address)
.InstanceEntity;
另一个解决方案是获取属性所有者并使用反射调用属性设置器。这个解决方案的优点是它不使用扩展方法,可以用任何类型调用。
private void SetPropertyValue(Expression<Func<object, object>> lambda, object value)
{
var memberExpression = (MemberExpression)lambda.Body;
var propertyInfo = (PropertyInfo)memberExpression.Member;
var propertyOwnerExpression = (MemberExpression)memberExpression.Expression;
var propertyOwner = Expression.Lambda(propertyOwnerExpression).Compile().DynamicInvoke();
propertyInfo.SetValue(propertyOwner, value, null);
}
...
SetPropertyValue(s => myStuff.MyPropy, newValue);
这是我使用Expression.Assign
的解决方案,但仔细观察后,接受的答案同样好。
// optionally or additionally put in a class<T> to capture the object type once
// and then you don't have to repeat it if you have a lot of properties
public Action<T, TProperty> GetSetter<T, TProperty>(
Expression<Func<T, TProperty>> pExpression
) {
var parameter1 = Expression.Parameter(typeof(T));
var parameter2 = Expression.Parameter(typeof(TProperty));
// turning an expression body into a PropertyInfo is common enough
// that it's a good idea to extract this to a reusable method
var member = (MemberExpression)pExpression.Body;
var propertyInfo = (PropertyInfo)member.Member;
// use the PropertyInfo to make a property expression
// for the first parameter (the object)
var property = Expression.Property(parameter1, propertyInfo);
// assignment expression that assigns the second parameter (value) to the property
var assignment = Expression.Assign(property, parameter2);
// then just build the lambda, which takes 2 parameters, and has the assignment
// expression for its body
var setter = Expression.Lambda<Action<T, TProperty>>(
assignment,
parameter1,
parameter2
);
return setter.Compile();
}
你可以做的另一件事是封装它们:
public sealed class StrongProperty<TObject, TProperty> {
readonly PropertyInfo mPropertyInfo;
public string Name => mPropertyInfo.Name;
public Func<TObject, TProperty> Get { get; }
public Action<TObject, TProperty> Set { get; }
// maybe other useful properties
internal StrongProperty(
PropertyInfo pPropertyInfo,
Func<TObject, TProperty> pGet,
Action<TObject, TProperty> pSet
) {
mPropertyInfo = pPropertyInfo;
Get = pGet;
Set = pSet;
}
}
现在你可以传递这些,类似于委托,并编写逻辑可以随属性变化的代码。这就解决了不能通过引用传递属性的问题。
这就是我的想法,我为我工作了这段代码,考虑到svick的贡献:
public class FactoryEntity<TEntity> where TEntity : Entity, new()
{
private TEntity _Entity;
public FactoryEntity()
{
_Entity = new TEntity();
}
public TEntity Build()
{
if (_Entity.IsValid())
throw new Exception("_Entity.Id");
return _Entity;
}
public FactoryEntity<TEntity> AssociateWithEntity<TProperty>(Expression<Func<TEntity, TProperty>> foreignEntity, TProperty instanceEntity) where TProperty : Entity
{
if (instanceEntity == null || instanceEntity.IsTransient())
throw new ArgumentNullException();
SetObjectValue<TEntity, TProperty>(_Entity, foreignEntity, instanceEntity);
return this;
}
private void SetObjectValue<T, TResult>(object target, Expression<Func<T, TResult>> expression, TResult value)
{
var memberExpression = (MemberExpression)expression.Body;
var propertyInfo = (PropertyInfo)memberExpression.Member;
var newValue = Convert.ChangeType(value, value.GetType());
propertyInfo.SetValue(target, newValue, null);
}
}
在这里,我调用工厂来在有效的
中构建Person对象。Person person = new FactoryEntity<Person>().AssociateWithEntity(p=>p.Address, address).Build();
但是我不知道这段代码是否是最佳的,至少我不调用compile()方法,在说什么?
谢谢
我制作了混合Rytis I溶液和https://stackoverflow.com/a/12423256/254109
private static void SetPropertyValue<T>(Expression<Func<T>> lambda, object value)
{
var memberExpression = (MemberExpression)lambda.Body;
var propertyInfo = (PropertyInfo)memberExpression.Member;
var propertyOwnerExpression = (MemberExpression)memberExpression.Expression;
var propertyOwner = Expression.Lambda(propertyOwnerExpression).Compile().DynamicInvoke();
propertyInfo.SetValue(propertyOwner, value, null);
}
命名为
SetPropertyValue(() => myStuff.MyProp, newValue);
一切都简单多了:
public static Action<T, TValue> GetSetter<T, TValue>(
Expression<Func<T, TValue>> expression)
{
var parameter = Expression.Parameter(typeof(TValue), "value");
var setterLambda = Expression.Lambda<Action<T, TValue>>(
Expression.Assign(expression.Body, parameter),
expression.Parameters[0],
parameter);
return setterLambda.Compile();
}