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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<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
到此，相信大家对“C#使用表达式树怎么实现对象复制”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
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