自动将一个对象的属性值应用到另一个相同类型

问题描述

给定类型为 T 的 2 个对象 A 和 B，我想将 A 中的属性值分配给 B 中的相同属性，而不对每个属性进行显式分配.

Given 2 objects A and B of type T, I want to assign the properties' values in A to the same properties in B without doing an explicit assignment for each property.

我想这样保存代码:

b.Nombre = a.Nombre;
b.Descripcion = a.Descripcion;
b.Imagen = a.Imagen;
b.Activo = a.Activo;

做类似的事情

a.ApplyProperties(b);

有可能吗?

推荐答案

我在 MiscUtil 调用了 PropertyCopy，它执行类似的操作 - 尽管它创建了目标类型的新实例并将属性复制到其中.

I have a type in MiscUtil called PropertyCopy which does something similar - although it creates a new instance of the target type and copies the properties into that.

它不要求类型相同——它只是将所有可读属性从源"类型复制到目标"类型.当然，如果类型相同，那更有可能起作用:) 这是一个浅拷贝，顺便说一句.

It doesn't require the types to be the same - it just copies all the readable properties from the "source" type to the "target" type. Of course if the types are the same, that's more likely to work :) It's a shallow copy, btw.

在此答案底部的代码块中，我扩展了类的功能.为了从一个实例复制到另一个实例，它在执行时使用简单的 PropertyInfo 值 - 这比使用表达式树慢，但另一种方法是编写一个动态方法，我不太喜欢热.如果性能对您来说绝对至关重要，请告诉我，我会看看我能做些什么.要使用该方法，请编写如下内容:

In the code block at the bottom of this answer, I've extended the capabilities of the class. To copy from one instance to another, it uses simple PropertyInfo values at execution time - this is slower than using an expression tree, but the alternative would be to write a dynamic method, which I'm not too hot on. If performance is absolutely critical for you, let me know and I'll see what I can do. To use the method, write something like:

MyType instance1 = new MyType();
// Do stuff
MyType instance2 = new MyType();
// Do stuff

PropertyCopy.Copy(instance1, instance2);

(其中 Copy 是使用类型推断调用的通用方法).

(where Copy is a generic method called using type inference).

我还没有准备好发布完整的 MiscUtil，但这是更新后的代码，包括注释.我不会为 SO 编辑器重新包装它们 - 只需复制整个块.

I'm not really ready to do a full MiscUtil release, but here's the updated code, including comments. I'm not going to rewrap them for the SO editor - just copy the whole chunk.

(如果我从头开始，我也可能会在命名方面重新设计 API，但我不想破坏现有用户......)

(I'd also probably redesign the API a bit in terms of naming if I were starting from scratch, but I don't want to break existing users...)

#if DOTNET35
using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;

namespace MiscUtil.Reflection
{
    /// <summary>
    /// Non-generic class allowing properties to be copied from one instance
    /// to another existing instance of a potentially different type.
    /// </summary>
    public static class PropertyCopy
    {
        /// <summary>
        /// Copies all public, readable properties from the source object to the
        /// target. The target type does not have to have a parameterless constructor,
        /// as no new instance needs to be created.
        /// </summary>
        /// <remarks>Only the properties of the source and target types themselves
        /// are taken into account, regardless of the actual types of the arguments.</remarks>
        /// <typeparam name="TSource">Type of the source</typeparam>
        /// <typeparam name="TTarget">Type of the target</typeparam>
        /// <param name="source">Source to copy properties from</param>
        /// <param name="target">Target to copy properties to</param>
        public static void Copy<TSource, TTarget>(TSource source, TTarget target)
            where TSource : class
            where TTarget : class
        {
            PropertyCopier<TSource, TTarget>.Copy(source, target);
        }
    }

    /// <summary>
    /// Generic class which copies to its target type from a source
    /// type specified in the Copy method. The types are specified
    /// separately to take advantage of type inference on generic
    /// method arguments.
    /// </summary>
    public static class PropertyCopy<TTarget> where TTarget : class, new()
    {
        /// <summary>
        /// Copies all readable properties from the source to a new instance
        /// of TTarget.
        /// </summary>
        public static TTarget CopyFrom<TSource>(TSource source) where TSource : class
        {
            return PropertyCopier<TSource, TTarget>.Copy(source);
        }
    }

    /// <summary>
    /// Static class to efficiently store the compiled delegate which can
    /// do the copying. We need a bit of work to ensure that exceptions are
    /// appropriately propagated, as the exception is generated at type initialization
    /// time, but we wish it to be thrown as an ArgumentException.
    /// Note that this type we do not have a constructor constraint on TTarget, because
    /// we only use the constructor when we use the form which creates a new instance.
    /// </summary>
    internal static class PropertyCopier<TSource, TTarget>
    {
        /// <summary>
        /// Delegate to create a new instance of the target type given an instance of the
        /// source type. This is a single delegate from an expression tree.
        /// </summary>
        private static readonly Func<TSource, TTarget> creator;

        /// <summary>
        /// List of properties to grab values from. The corresponding targetProperties 
        /// list contains the same properties in the target type. Unfortunately we can't
        /// use expression trees to do this, because we basically need a sequence of statements.
        /// We could build a DynamicMethod, but that's significantly more work :) Please mail
        /// me if you really need this...
        /// </summary>
        private static readonly List<PropertyInfo> sourceProperties = new List<PropertyInfo>();
        private static readonly List<PropertyInfo> targetProperties = new List<PropertyInfo>();
        private static readonly Exception initializationException;

        internal static TTarget Copy(TSource source)
        {
            if (initializationException != null)
            {
                throw initializationException;
            }
            if (source == null)
            {
                throw new ArgumentNullException("source");
            }
            return creator(source);
        }

        internal static void Copy(TSource source, TTarget target)
        {
            if (initializationException != null)
            {
                throw initializationException;
            }
            if (source == null)
            {
                throw new ArgumentNullException("source");
            }
            for (int i = 0; i < sourceProperties.Count; i++)
            {
                targetProperties[i].SetValue(target, sourceProperties[i].GetValue(source, null), null);
            }

        }

        static PropertyCopier()
        {
            try
            {
                creator = BuildCreator();
                initializationException = null;
            }
            catch (Exception e)
            {
                creator = null;
                initializationException = e;
            }
        }

        private static Func<TSource, TTarget> BuildCreator()
        {
            ParameterExpression sourceParameter = Expression.Parameter(typeof(TSource), "source");
            var bindings = new List<MemberBinding>();
            foreach (PropertyInfo sourceProperty in typeof(TSource).GetProperties(BindingFlags.Public | BindingFlags.Instance))
            {
                if (!sourceProperty.CanRead)
                {
                    continue;
                }
                PropertyInfo targetProperty = typeof(TTarget).GetProperty(sourceProperty.Name);
                if (targetProperty == null)
                {
                    throw new ArgumentException("Property " + sourceProperty.Name + " is not present and accessible in " + typeof(TTarget).FullName);
                }
                if (!targetProperty.CanWrite)
                {
                    throw new ArgumentException("Property " + sourceProperty.Name + " is not writable in " + typeof(TTarget).FullName);
                }
                if ((targetProperty.GetSetMethod().Attributes & MethodAttributes.Static) != 0)
                {
                    throw new ArgumentException("Property " + sourceProperty.Name + " is static in " + typeof(TTarget).FullName);
                }
                if (!targetProperty.PropertyType.IsAssignableFrom(sourceProperty.PropertyType))
                {
                    throw new ArgumentException("Property " + sourceProperty.Name + " has an incompatible type in " + typeof(TTarget).FullName);
                }
                bindings.Add(Expression.Bind(targetProperty, Expression.Property(sourceParameter, sourceProperty)));
                sourceProperties.Add(sourceProperty);
                targetProperties.Add(targetProperty);
            }
            Expression initializer = Expression.MemberInit(Expression.New(typeof(TTarget)), bindings);
            return Expression.Lambda<Func<TSource, TTarget>>(initializer, sourceParameter).Compile();
        }
    }
}
#endif

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