C#使用表达式树怎么实现对象复制

本篇内容主要讲解"C#使用表达式树怎么实现对象复制"，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习"C#使用表达式树怎么实现对象复制"吧!

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 copiers = new ConcurrentDictionary();        /// 
        /// 复制两个对象同名属性值        /// 
        ///         ///         /// 源对象        /// 目标对象        /// 源对象属性值为null时，是否将值复制给目标对象        public static void Copy(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 copier = CreateCopier(copyNull);                copiers.TryAdd(name, copier);                targetCopier = copier;            }            Action action = (Action)targetCopier;            action(source, target);        }        /// 
        /// 为指定的两种类型编译生成属性复制委托        /// 
        ///         ///         /// 源对象属性值为null时，是否将值复制给目标对象        ///         private static Action CreateCopier(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 expressionList = new List();            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> lambda = Lambda>(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    {        static Action action = CreateCopier();        /// 
        /// 复制两个对象同名属性值        /// 
        ///         ///         /// 源对象        /// 目标对象        /// 源对象属性值为null时，是否将值复制给目标对象        public static void Copy(S source, T target, bool copyNull = true)        {            action(source, target);        }        /// 
        /// 为指定的两种类型编译生成属性复制委托        /// 
        ///         ///         /// 源对象属性值为null时，是否将值复制给目标对象        ///         private static Action 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> lambda = Expression.Lambda>(block, source, target);            return lambda.Compile();        }    }}

百万次耗时：100ms左右

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