表达式<Func<TModel,string>> 到表达式<Action<TModel>> “Getter” 到 “Setter”
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【中文标题】表达式<Func<TModel,string>> 到表达式<Action<TModel>> “Getter” 到 “Setter”【英文标题】：Expression<Func<TModel,string>> to Expression<Action<TModel>> "Getter" to "Setter" 【发布时间】：2011-10-11 09:10:54 【问题描述】：我是表达式的新手，我想知道如何以任何方式转换我的表达式
假设在这个例子中我的 TModel 是 Customer 类型，并把它分配到这样的地方：
Expression<Func<TModel, string>> getvalueexpression = customer =>customer.Name
类似
Expression<Action<TModel,string>> setvalueexpression = [PSEUDOCODE] getvalueexpression = input
Action<TModel,string> Setter = setvalueexpression.Compile();
Setter(mycustomer,value);
简而言之，我想以某种方式构建和编译一个表达式，将我的 getter 表达式指定的客户名称设置为特定值。
【问题讨论】：
如果没有getter（即属性只有setter）会怎样？ 我不是在这里创建一个通用的解决方案。我计划使用它的属性将具有可访问的 getter 和 setter，我只是想知道如何构建 Setter 看看这个问题的第一个答案。 ***.com/questions/2823236/… 也许你应该选择另一个方向——从 setter 到 getter。 基于CreateDelegate 的方法通常比编译基于表达式树的方法更快。我还建议在***.com/questions/2823236/… 或我这里***.com/a/16078960/661933 中的 Marc 的回答中提到的那个。
【参考方案1】：
修改版。这个类可能比你可以找到的许多其他类更好:-) 这是因为这个版本支持直接属性（p => p.B）（和其他人一样:-)）、嵌套属性（p => p.B.C.D）、字段（两者都是“终端”和“中间”，所以在p => p.B.C.D 中B 和D 都可以是字段）和类型的“内部”转换（所以p => ((BType)p.B).C.D 和p => (p.B as BType).C.D)。唯一不是支持的是“终端”元素的转换（所以没有p => (object)p.B）。
生成器中有两个“代码路径”：用于简单表达式 (p => p.B) 和用于“嵌套”表达式。 .NET 4.0 有代码变体（具有 Expression.Assign 表达式类型）。从我的一些基准测试中，最快的代表是：“简单”Delegate.CreateDelegate 用于属性，Expression.Assign 用于字段，“简单”FieldSetter 用于字段（这个比Expression.Assign 字段慢一点）。所以在.NET 4.0下你应该去掉所有标记为3.5的代码。
部分代码不是我的。初始（简单）版本基于 Fluent NHibernate 代码（但它仅支持直接属性），其他一些部分基于来自 How do I set a field value in an C# Expression tree? 和 Assignment in .NET 3.5 expression trees 的代码。
public static class FluentTools
public static Action<T, TValue> GetterToSetter<T, TValue>(Expression<Func<T, TValue>> getter)
ParameterExpression parameter;
Expression instance;
MemberExpression propertyOrField;
GetMemberExpression(getter, out parameter, out instance, out propertyOrField);
// Very simple case: p => p.Property or p => p.Field
if (parameter == instance)
if (propertyOrField.Member.MemberType == MemberTypes.Property)
// This is FASTER than Expression trees! (5x on my benchmarks) but works only on properties
PropertyInfo property = propertyOrField.Member as PropertyInfo;
MethodInfo setter = property.GetSetMethod();
var action = (Action<T, TValue>)Delegate.CreateDelegate(typeof(Action<T, TValue>), setter);
return action;
#region .NET 3.5
else // if (propertyOrField.Member.MemberType == MemberTypes.Field)
// 1.2x slower than 4.0 method, 5x faster than 3.5 method
FieldInfo field = propertyOrField.Member as FieldInfo;
var action = FieldSetter<T, TValue>(field);
return action;
#endregion
ParameterExpression value = Expression.Parameter(typeof(TValue), "val");
Expression expr = null;
#region .NET 3.5
if (propertyOrField.Member.MemberType == MemberTypes.Property)
PropertyInfo property = propertyOrField.Member as PropertyInfo;
MethodInfo setter = property.GetSetMethod();
expr = Expression.Call(instance, setter, value);
else // if (propertyOrField.Member.MemberType == MemberTypes.Field)
expr = FieldSetter(propertyOrField, value);
#endregion
//#region .NET 4.0
//// For field access it's 5x faster than the 3.5 method and 1.2x than "simple" method. For property access nearly same speed (1.1x faster).
//expr = Expression.Assign(propertyOrField, value);
//#endregion
return Expression.Lambda<Action<T, TValue>>(expr, parameter, value).Compile();
private static void GetMemberExpression<T, U>(Expression<Func<T, U>> expression, out ParameterExpression parameter, out Expression instance, out MemberExpression propertyOrField)
Expression current = expression.Body;
while (current.NodeType == ExpressionType.Convert || current.NodeType == ExpressionType.TypeAs)
current = (current as UnaryExpression).Operand;
if (current.NodeType != ExpressionType.MemberAccess)
throw new ArgumentException();
propertyOrField = current as MemberExpression;
current = propertyOrField.Expression;
instance = current;
while (current.NodeType != ExpressionType.Parameter)
if (current.NodeType == ExpressionType.Convert || current.NodeType == ExpressionType.TypeAs)
current = (current as UnaryExpression).Operand;
else if (current.NodeType == ExpressionType.MemberAccess)
current = (current as MemberExpression).Expression;
else
throw new ArgumentException();
parameter = current as ParameterExpression;
#region .NET 3.5
// Based on https://***.com/questions/321650/how-do-i-set-a-field-value-in-an-c-expression-tree/321686#321686
private static Action<T, TValue> FieldSetter<T, TValue>(FieldInfo field)
DynamicMethod m = new DynamicMethod("setter", typeof(void), new Type[] typeof(T), typeof(TValue) , typeof(FluentTools));
ILGenerator cg = m.GetILGenerator();
// arg0.<field> = arg1
cg.Emit(OpCodes.Ldarg_0);
cg.Emit(OpCodes.Ldarg_1);
cg.Emit(OpCodes.Stfld, field);
cg.Emit(OpCodes.Ret);
return (Action<T, TValue>)m.CreateDelegate(typeof(Action<T, TValue>));
// Based on https://***.com/questions/208969/assignment-in-net-3-5-expression-trees/3972359#3972359
private static Expression FieldSetter(Expression left, Expression right)
return
Expression.Call(
null,
typeof(FluentTools)
.GetMethod("AssignTo", BindingFlags.NonPublic | BindingFlags.Static)
.MakeGenericMethod(left.Type),
left,
right);
private static void AssignTo<T>(ref T left, T right) // note the 'ref', which is
// important when assigning
left = right; // to value types!
#endregion
【讨论】：
这看起来很有希望，我在 CreateDelegate 调用中遇到了一个参数异常，“错误绑定到目标方法。”调试模式下的表达式有一个 NodeType 参数，我要设置的成员是 DateTime @Mvision 你想绑定什么？这仅适用于公共属性。 我假设我绑定的所有属性都是公开的，我从 EF4 实体中挑选它们，如下所示：customer=>customer.DateCreated 等 @Mvision 在这里它可以正常工作。我刚刚生成了一个 EF 模型来测试它。尝试查看 DateCreated 的定义（右键单击，转到定义） public global::System.DateTime Datecreated，我使用“object”作为 U 很难，因为我不确定该值是什么类型，可能是这样吗？【参考方案2】：static Expression<Action<T, TProperty>> MakeSetter<T, TProperty>(Expression<Func<T, TProperty>> getter)
var memberExpr = (MemberExpression)getter.Body;
var @this = Expression.Parameter(typeof(T), "$this");
var value = Expression.Parameter(typeof(TProperty), "value");
return Expression.Lambda<Action<T, TProperty>>(
Expression.Assign(Expression.MakeMemberAccess(@this, memberExpr.Member), value),
@this, value);
【讨论】：
【参考方案3】：我有这个帮助方法，它返回属性的属性信息：
public static PropertyInfo GetPropertyInfo<T, U>(Expression<Func<T, U>> property) where T : class
var memberExpression = (property.Body as MemberExpression);
if (memberExpression != null && memberExpression.Member is PropertyInfo)
return memberExpression.Member as PropertyInfo;
throw new InvalidOperationException("Invalid usage of GetPropertyInfo");
用法：GetPropertyInfo((MyClass c) => c.PropertyName);
然后您可以使用 PropertyInfo 设置类的属性值。
您需要修改代码以满足您的需要，但希望它会有所帮助。
【讨论】：
【参考方案4】：由于正确的答案对我不起作用（表达式中的集合）但将我推向了正确的方向，我需要对此进行大量调查，我想我想出了一种可以为几乎任何成员表达。
对于属性和字段，它的行为与标记的答案相同（但我相信它更加透明）。
它对列表和字典有额外的支持 - 请在 cmets 中查看。
public static Action<TObject, TPropertyOnObject> GetSetter<TObject, TPropertyOnObject>(Expression<Func<TObject, TPropertyOnObject>> getterExpression)
/*** SIMPLE PROPERTIES AND FIELDS ***/
// check if the getter expression refers directly to a PROPERTY or FIELD
var memberAcessExpression = getterExpression.Body as MemberExpression;
if (memberAcessExpression != null)
//to here we assign the SetValue method of a property or field
Action<object, object> propertyOrFieldSetValue = null;
// property
var propertyInfo = memberAcessExpression.Member as PropertyInfo;
if (propertyInfo != null)
propertyOrFieldSetValue = (declaringObjectInstance, propertyOrFieldValue) => propertyInfo.SetValue(declaringObjectInstance, propertyOrFieldValue);
;
// field
var fieldInfo = memberAcessExpression.Member as FieldInfo;
if (fieldInfo != null)
propertyOrFieldSetValue = (declaringObjectInstance, propertyOrFieldValue) => fieldInfo.SetValue(declaringObjectInstance, propertyOrFieldValue);
// This is the expression to get declaring object instance.
// Example: for expression "o=>o.Property1.Property2.CollectionProperty[3].TargetProperty" it gives us the "o.Property1.Property2.CollectionProperty[3]" part
var memberAcessExpressionCompiledLambda = Expression.Lambda(memberAcessExpression.Expression, getterExpression.Parameters.Single()).Compile();
Action<TObject, TPropertyOnObject> setter = (expressionParameter, value) =>
// get the object instance on which is the property we want to set
var declaringObjectInstance = memberAcessExpressionCompiledLambda.DynamicInvoke(expressionParameter);
Debug.Assert(propertyOrFieldSetValue != null, "propertyOrFieldSetValue != null");
// set the value of the property
propertyOrFieldSetValue(declaringObjectInstance, value);
;
return setter;
/*** COLLECTIONS ( IDictionary<,> and IList<,>) ***/
/*
* DICTIONARY:
* Sample expression:
* "myObj => myObj.Property1.ListProperty[5].AdditionalInfo["KEY"]"
* Setter behaviour:
* The same as adding to a dictionary.
* It does Add("KEY", <value to be set>) to the dictionary. It fails if the jey already exists.
*
*
* LIST
* Sample expression:
* "myObj => myObj.Property1.ListProperty[INDEX]"
* Setter behaviour:
* If INDEX >= 0 and the index exists in the collection it behaves the same like inserting to a collection.
* IF INDEX < 0 (is negative) it adds the value at the end of the collection.
*/
var methodCallExpression = getterExpression.Body as MethodCallExpression;
if (
methodCallExpression != null && methodCallExpression.Object != null &&
methodCallExpression.Object.Type.IsGenericType)
var collectionGetterExpression = methodCallExpression.Object as MemberExpression;
Debug.Assert(collectionGetterExpression != null, "collectionGetterExpression != null");
// This gives us the collection instance when it is invoked on the object instance whic the expression is for
var collectionGetterCompiledLambda =Expression.Lambda(collectionGetterExpression, getterExpression.Parameters.Single()).Compile();
// this returns the "KEY" which is the key (object) in case of Dictionaries and Index (integer) in case of other collections
var collectionKey = ((ConstantExpression) methodCallExpression.Arguments[0]).Value;
var collectionType = collectionGetterExpression.Type;
// IDICTIONARY
if (collectionType.GetGenericTypeDefinition() == typeof(IDictionary<,>))
// Create an action which accepts the instance of the object which the "dictionary getter" expression is for and a value
// to be added to the dictionary.
Action<TObject, TPropertyOnObject> dictionaryAdder = (expressionParameter, value) =>
try
var dictionaryInstance = (IDictionary)collectionGetterCompiledLambda.DynamicInvoke(expressionParameter);
dictionaryInstance.Add(collectionKey, value);
catch (Exception exception)
throw new Exception(
string.Format(
"Addition to dictionary failed [Key='0', Value='1']. The \"adder\" was generated from getter expression: '2'.",
collectionKey,
value,
getterExpression.ToString()), exception);
;
return dictionaryAdder;
// ILIST
if (typeof (IList<>).MakeGenericType(typeof (bool)).IsAssignableFrom(collectionType.GetGenericTypeDefinition().MakeGenericType(typeof(bool))))
// Create an action which accepts the instance of the object which the "collection getter" expression is for and a value
// to be inserted
Action<TObject, TPropertyOnObject> collectionInserter = (expressionParameter, value) =>
try
var collectionInstance = (IList<TPropertyOnObject>)collectionGetterCompiledLambda.DynamicInvoke(expressionParameter);
var collectionIndexFromExpression = int.Parse(collectionKey.ToString());
// The semantics of a collection setter is to add value if the index in expression is <0 and set the item at the index
// if the index >=0.
if (collectionIndexFromExpression < 0)
collectionInstance.Add(value);
else
collectionInstance[collectionIndexFromExpression] = value;
catch (Exception invocationException)
throw new Exception(
string.Format(
"Insertion to collection failed [Index='0', Value='1']. The \"inserter\" was generated from getter expression: '2'.",
collectionKey,
value,
getterExpression.ToString()), invocationException);
;
return collectionInserter;
throw new NotSupportedException(
string.Format(
"Cannot generate setter from the given expression: '0'. Collection type: '1' not supported.",
getterExpression, collectionType));
throw new NotSupportedException("Cannot generate setter from the given expression: "+getterExpression);
【讨论】：
【参考方案5】：这是我的方式
public static Action<T, object> GenerateSetterAction<T>(PropertyInfo pi)
//p=> p.<pi>=(pi.PropertyType)v
var expParamP = Expression.Parameter(typeof(T), "p");
var expParamV = Expression.Parameter(typeof(object), "v");
var expParamVc = Expression.Convert(expParamV, pi.PropertyType);
var mma = Expression.Call(
expParamP
, pi.GetSetMethod()
, expParamVc
);
var exp = Expression.Lambda<Action<T, object>>(mma, expParamP, expParamV);
return exp.Compile();
【讨论】：
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