C#使用表達式樹(LambdaExpression)動態更新類的屬性值(示例代碼)
有看過我之前發表過的C#相關文章分享和閱讀過我代碼的朋友們可能會在我的代碼裡面經常看到各種各樣的λ表達式動態拼接，C#的λ表達式樹是一個好東西，也是別的語言學不來的，熟悉掌握λ表達式就能夠實現各種場景的個性化操作，如動態拼接查詢條件、排序方式等，也能夠實現替代反射的高性能操作，比如我們常用到的IQueryable和IEnumerable，每個擴展方法就全是λ表達式樹。
本文給大傢分享C#使用表達式樹(LambdaExpression)動態更新類的屬性值的相關知識，在某些業務中會遇到需要同步兩個類的屬性值的情況，而且有些字段是要過濾掉的。如果手動賦值則需要寫很多重復的代碼：
public class Teacher
{
public Guid Id { get; set; }
public string Name { get; set; }
public string Age { get; set; }
}
public class Student
{
public Guid Id { get; set; }
public string Name { get; set; }
public string Age { get; set; }
}
/// <summary>
/// 比如需要把teacher的某些屬性值賦給student，而id不需要賦值
/// </summary>
/// <param name="student"></param>
/// <param name="teacher"></param>
public static void SetProperty(Student student, Teacher teacher)
{
if (student.Name != teacher.Name)
{
student.Name = teacher.Name;
}
if (student.Age != teacher.Age)
{
student.Age = teacher.Age;
}
}
使用反射的話性能考慮，嘗試寫一個擴展方法使用lambda表達式樹去構建一個方法
public static class ObjectExtensions
{
/// <summary>
/// 緩存表達式
/// </summary>
/// <typeparam name="TSource"></typeparam>
/// <typeparam name="TTarget"></typeparam>
public static class MapperAccessor<TSource, TTarget>
{
private static Action<TSource, TTarget, string[]> func { get; set; }
public static TSource Set(TSource source, TTarget target, params string[] properties)
{
if (func == null)
{
var sourceType = typeof(TSource);
var targetType = typeof(TTarget);
BindingFlags bindingFlags = BindingFlags.Instance | BindingFlags.Public;
if (properties.Length == 0)
{
//get all properties
if (sourceType == targetType)
{
//如果是相同類型則獲取所有屬性
properties = sourceType.GetProperties(bindingFlags).Select(x => x.Name)
.ToArray();
}
else
{
//如果沒有傳指定的屬性則默認獲取同名屬性
List<PropertyInfo> propertyInfos = new List<PropertyInfo>();
foreach (var property in sourceType.GetProperties(bindingFlags))
{//不同類型指定同名且類型相同的屬性
var targetProperty = targetType.GetProperty(property.Name, bindingFlags);
if (targetProperty != null && targetProperty.PropertyType == property.PropertyType)
{
propertyInfos.Add(property);
}
}
properties = propertyInfos.Select(x => x.Name).ToArray();
}
}
//定義lambda 3個參數
var s = Expression.Parameter(typeof(TSource), "s");
var t = Expression.Parameter(typeof(TTarget), "t");
var ps = Expression.Parameter(typeof(string[]), "ps");
//獲取泛型擴展方法Contains
var methodInfo = typeof(Enumerable).GetMethods().FirstOrDefault(e => e.Name == "Contains" && e.GetParameters().Length == 2);
if (methodInfo == null)
{
// properties.Contains()
throw new NullReferenceException(nameof(methodInfo));
}
MethodInfo genericMethod = methodInfo.MakeGenericMethod(typeof(String));//創建泛型方法
List<BlockExpression> bs = new List<BlockExpression>();
foreach (string field in properties)
{
//獲取兩個類型裡面的屬性
var sourceField = Expression.Property(s, field);
var targetField = Expression.Property(t, field);
//創建一個條件表達式
var notEqual = Expression.NotEqual(sourceField, targetField);//sourceField!=targetField
var method = Expression.Call(null, genericMethod, ps, Expression.Constant(field));//ps.Contains(f);
//構建賦值語句
var ifTrue = Expression.Assign(sourceField, targetField);
//拼接表達式 sourceField!=targetField&&ps.Contains(f)
var condition = Expression.And(notEqual, Expression.IsTrue(method));
//判斷是否相同，如果不相同則賦值
var expression = Expression.IfThen(condition, ifTrue);
bs.Add(Expression.Block(expression));
}
var lambda = Expression.Lambda<Action<TSource, TTarget, string[]>>(Expression.Block(bs), s, t, ps);
func = lambda.Compile();
}
func.Invoke(source, target, properties);
return source;
}
}
/// <summary>
/// 通過目標類更新源類同名屬性值
/// </summary>
/// <typeparam name="TSource">待更新的數據類型</typeparam>
/// <typeparam name="TTarget">目標數據類型</typeparam>
/// <param name="source">源數據</param>
/// <param name="target">目標數據</param>
/// <param name="properties">要變更的屬性名稱</param>
/// <returns>返回源數據，更新後的</returns>
public static TSource SetProperties<TSource, TTarget>(this TSource source, TTarget target, params string[] properties)
{
return MapperAccessor<TSource, TTarget>.Set(source, target, properties);
}
}
編寫測試方法
/// <summary>
/// 比如需要把teacher的某些屬性值賦給student，而id不需要賦值
/// </summary>
/// <param name="student"></param>
/// <param name="teacher"></param>
public static void SetProperty(Student student, Teacher teacher)
{
if (student.Name != teacher.Name)
{
student.Name = teacher.Name;
}
if (student.Age != teacher.Age)
{
student.Age = teacher.Age;
}
}
public static void SetProperty2(Student student, Teacher teacher, params string[] properties)
{
var sourceType = student.GetType();
var targetType = teacher.GetType();
foreach (var property in properties)
{
var aP = sourceType.GetProperty(property);
var bP = targetType.GetProperty(property);
var apValue = aP.GetValue(student);
var bpValue = bP.GetValue(teacher);
if (apValue != bpValue)
{
aP.SetValue(student, bpValue);
}
}
}
static (List<Student>, List<Teacher>) CreateData(int length)
{
var rd = new Random();
(List<Student>, List<Teacher>) ret;
ret.Item1 = new List<Student>();
ret.Item2 = new List<Teacher>();
for (int i = 0; i < length; i++)
{
Student student = new Student()
{
Id = Guid.NewGuid(),
Name = Guid.NewGuid().ToString("N"),
Age = rd.Next(1, 100)
};
ret.Item1.Add(student);
Teacher teacher = new Teacher()
{
Id = Guid.NewGuid(),
Name = Guid.NewGuid().ToString("N"),
Age = rd.Next(1, 100)
};
ret.Item2.Add(teacher);
}
return ret;
}
static void Main(string[] args)
{
var length = 1000000;
var data = CreateData(length);
Stopwatch sw = new Stopwatch();
sw.Start();
for (int i = 0; i < length; i++)
{
SetProperty(data.Item1[i], data.Item2[i]);
}
sw.Stop();
Console.WriteLine($"手寫方法耗時：{sw.ElapsedMilliseconds}ms");
data.Item1.Clear();
data.Item2.Clear();
var data2 = CreateData(length);
sw.Restart();
for (int i = 0; i < length; i++)
{
data2.Item1[i].SetProperties(data2.Item2[i], nameof(Student.Age), nameof(Student.Name));
}
data2.Item1.Clear();
data2.Item2.Clear();
sw.Stop();
Console.WriteLine($"lambda耗時：{sw.ElapsedMilliseconds}ms");
var data3 = CreateData(length);
sw.Restart();
for (int i = 0; i < length; i++)
{
SetProperty2(data3.Item1[i], data3.Item2[i], nameof(Student.Age), nameof(Student.Name));
}
sw.Stop();
Console.WriteLine($"反射耗時：{sw.ElapsedMilliseconds}ms");
data3.Item1.Clear();
data3.Item2.Clear();
Console.ReadKey();
}
可以看到性能和手寫方法之間的差距，如果要求比較高還是手寫方法，如果字段多的話寫起來是很痛苦的事。但是日常用這個足夠瞭，而且是擴展方法，通用性很強。
到此這篇關於C#使用表達式樹(LambdaExpression)動態更新類的屬性值的文章就介紹到這瞭,更多相關C#表達式樹類的屬性值內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet！
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