C#使用表达式树实现对象复制的示例代码

需求背景：对象复制性能优化；同时，在对象复制时，应跳过引用类型的null值复制，值类型支持值类型向可空类型的复制

using Common;
using System;
class Program
{
    static void Main(string[] args)
    {
        TestClassA classA = new TestClassA() { PropA = new TestClass() { Name = "cs1" }, PropB = "c1", PropC = 1 };
        TestClassA classB = new TestClassA() { PropA = new TestClass() { Name = "cs2" }, PropB = "c2", PropC = 2 };
        FastCopy.Copy(classA, classB, false);
        Console.WriteLine(classB.PropA?.Name + ":" + classB.PropB + ":" + classB.PropC);
        TestClassA classC = new TestClassA() { PropA = new TestClass() { Name = "cs1" } };
        TestClassA classD = new TestClassA() { PropA = new TestClass() { Name = "cs2" }, PropB = "c2", PropC = 2 };
        FastCopy.Copy(classC, classD, false);
        Console.WriteLine(classD.PropA?.Name + ":" + classD.PropB + ":" + classD.PropC);
    }
}
public class TestClassA
{
    public TestClass PropA { get; set; }
    public string PropB { get; set; }
    public int? PropC { get; set; }
}
public class TestClass
{
    public string Name { get; set; }
}

输出：

百万次调用耗时：270-300ms

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using static System.Linq.Expressions.Expression;
namespace Common
{
    public static class FastCopy
    {
        static ConcurrentDictionary<string, object> copiers = new ConcurrentDictionary<string, object>();
        /// <summary>
        /// 复制两个对象同名属性值
        /// </summary>
        /// <typeparam name="S"></typeparam>
        /// <typeparam name="T"></typeparam>
        /// <param name="source">源对象</param>
        /// <param name="target">目标对象</param>
        /// <param name="copyNull">源对象属性值为null时，是否将值复制给目标对象</param>
        public static void Copy<S, T>(S source, T target, bool copyNull = true)
        {
            string name = string.Format("{0}_{1}_{2}", typeof(S), typeof(T), copyNull);
            object targetCopier;
            if (!copiers.TryGetValue(name, out targetCopier))
            {
                Action<S, T> copier = CreateCopier<S, T>(copyNull);
                copiers.TryAdd(name, copier);
                targetCopier = copier;
            }
            Action<S, T> action = (Action<S, T>)targetCopier;
            action(source, target);
        }
        /// <summary>
        /// 为指定的两种类型编译生成属性复制委托
        /// </summary>
        /// <typeparam name="S"></typeparam>
        /// <typeparam name="T"></typeparam>
        /// <param name="copyNull">源对象属性值为null时，是否将值复制给目标对象</param>
        /// <returns></returns>
        private static Action<S, T> CreateCopier<S, T>(bool copyNull)
        {
            ParameterExpression source = Parameter(typeof(S));
            ParameterExpression target = Parameter(typeof(T));
            var sourceProps = typeof(S).GetProperties(BindingFlags.Instance | BindingFlags.Public).Where(p => p.CanRead).ToList();
            var targetProps = typeof(T).GetProperties(BindingFlags.Instance | BindingFlags.Public).Where(p => p.CanWrite).ToList();
            // 查找可进行赋值的属性
            var copyProps = targetProps.Where(tProp => sourceProps.Where(sProp => sProp.Name == tProp.Name// 名称一致 且
            && (
            sProp.PropertyType == tProp.PropertyType// 属性类型一致 或
            || sProp.PropertyType.IsAssignableFrom(tProp.PropertyType) // 源属性类型 为 目标属性类型 的 子类；eg：object target = string source;   或
            || (tProp.PropertyType.IsValueType && sProp.PropertyType.IsValueType && // 属性为值类型且基础类型一致，但目标属性为可空类型 eg：int? num = int num;
            ((tProp.PropertyType.GenericTypeArguments.Length > 0 ? tProp.PropertyType.GenericTypeArguments[0] : tProp.PropertyType) == sProp.PropertyType))
            )).Count() > 0);
            List<Expression> expressionList = new List<Expression>();
            foreach (var prop in copyProps)
            {
                if (prop.PropertyType.IsValueType)// 属性为值类型
                {
                    PropertyInfo sProp = typeof(S).GetProperty(prop.Name);
                    PropertyInfo tProp = typeof(T).GetProperty(prop.Name);
                    if (sProp.PropertyType == tProp.PropertyType)// 属性类型一致 eg：int num = int num;    或   int? num = int? num;
                    {
                        var assign = Assign(Property(target, prop.Name), Property(source, prop.Name));
                        expressionList.Add(assign);
                    }
                    else if (sProp.PropertyType.GenericTypeArguments.Length <= 0 && tProp.PropertyType.GenericTypeArguments.Length > 0)// 属性类型不一致且目标属性类型为可空类型 eg：int? num = int num;
                    {
                        var convert = Convert(Expression.Property(source, prop.Name), tProp.PropertyType);
                        var cvAssign = Assign(Expression.Property(target, prop.Name), convert);
                        expressionList.Add(cvAssign);
                    }
                }
                else// 属性为引用类型
                {
                    var assign = Assign(Property(target, prop.Name), Property(source, prop.Name));// 编译生成属性赋值语句   target.{PropertyName} = source.{PropertyName};
                    var sourcePropIsNull = Equal(Constant(null, prop.PropertyType), Property(source, prop.Name));// 判断源属性值是否为Null；编译生成  source.{PropertyName} == null
                    var setNull = IsTrue(Constant(copyNull));// 判断是否复制Null值 编译生成  copyNull == True
                    var setNullTest = IfThen(setNull, assign);
                    var condition = IfThenElse(sourcePropIsNull, setNullTest, assign);
                    /**
                     * 编译生成
                     * if(source.{PropertyName} == null)
                     * {
                     *   if(setNull)
                     *   {
                     *     target.{PropertyName} = source.{PropertyName};
                     *   }
                     * }
                     * else
                     * {
                     *   target.{PropertyName} = source.{PropertyName};
                     * }
                     */
                    expressionList.Add(condition);
                }
            }
            var block = Block(expressionList.ToArray());
            Expression<Action<S, T>> lambda = Lambda<Action<S, T>>(block, source, target);
            return lambda.Compile();
        }
    }
}

如果完整复制，去掉逻辑判断，同时可通过泛型类，不在使用字典，性能还可以提升。

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
namespace Common
{
    public static class FastCopy<S, T>
    {
        static Action<S, T> action = CreateCopier();
        /// <summary>
        /// 复制两个对象同名属性值
        /// </summary>
        /// <typeparam name="S"></typeparam>
        /// <typeparam name="T"></typeparam>
        /// <param name="source">源对象</param>
        /// <param name="target">目标对象</param>
        /// <param name="copyNull">源对象属性值为null时，是否将值复制给目标对象</param>
        public static void Copy(S source, T target, bool copyNull = true)
        {
            action(source, target);
        }
        /// <summary>
        /// 为指定的两种类型编译生成属性复制委托
        /// </summary>
        /// <typeparam name="S"></typeparam>
        /// <typeparam name="T"></typeparam>
        /// <param name="copyNull">源对象属性值为null时，是否将值复制给目标对象</param>
        /// <returns></returns>
        private static Action<S, T> CreateCopier()
        {
            ParameterExpression source = Expression.Parameter(typeof(S));
            ParameterExpression target = Expression.Parameter(typeof(T));
            var sourceProps = typeof(S).GetProperties(BindingFlags.Instance | BindingFlags.Public).Where(p => p.CanRead).ToList();
            var targetProps = typeof(T).GetProperties(BindingFlags.Instance | BindingFlags.Public).Where(p => p.CanWrite).ToList();
            // 查找可进行赋值的属性
            var copyProps = targetProps.Where(tProp => sourceProps.Where(sProp => sProp.Name == tProp.Name// 名称一致 且
            && (
            sProp.PropertyType == tProp.PropertyType// 属性类型一致
            )).Count() > 0);
            var block = Expression.Block(from p in copyProps select Expression.Assign(Expression.Property(target, p.Name), Expression.Property(source, p.Name)));
            Expression<Action<S, T>> lambda = Expression.Lambda<Action<S, T>>(block, source, target);
            return lambda.Compile();
        }
    }
}

百万次耗时：100ms左右

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