如何設置屬性選擇器Expression的值 >

Question

如何設置屬性選擇器Expression的值 >

c# expression-trees linq

題

我需要使用模式工廠的想法將我的Person類實體中的實體屬性Address與我的FactoryEntities類中的表達式linq相關聯，看看這就是我擁有的和我想做的事情：

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*/
    }
}

Emilio Montes

熱門答案

您可以像這樣設置屬性：

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);
}

這僅適用於屬性，而不適用於字段，儘管添加對字段的支持應該很容易。

但是你獲得這個人的代碼是行不通的。如果你想保留AssociateWithEntity()的void返回類型，你可以這樣做：

var factory = new FactoryEntity<Person>();
factory.AssociateWithEntity(p => p.Address, address);
Person person = factory.InstanceEntity;

另一種選擇是流暢的界面：

Person person = new FactoryEntity<Person>()
    .AssociateWithEntity(p => p.Address, address)
    .InstanceEntity;

svick

在 Stack Overflow 上查看更多

smartcaveman · Accepted Answer · 6/16/2012 2:11:39 AM

這有效：

以下幫助器方法將getter表達式轉換為setter委託。如果要返回Expression<Action<T,TProperty>>而不是Action<T,TProperty> ，則不要在最後調用Compile()方法。

注意：代碼來自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();
    }

如何設置屬性選擇器Expression的值 >

題

Fastest Entity Framework Extensions

一般承認的答案

這有效：

熱門答案

Performance

Expression Evaluator