C# ExpressionTree方法将MemberInitExpression分配给属性
我正在尝试使用表达式树,这样我就可以选择使用实体框架映射到DTO,就像Include指令在DbSet(实现OData的OpenSorce项目的一部分)上工作一样 下面的代码表示一个测试用例C# ExpressionTree方法将MemberInitExpression分配给属性,c#,entity-framework-6,expression-trees,C#,Entity Framework 6,Expression Trees,我正在尝试使用表达式树,这样我就可以选择使用实体框架映射到DTO,就像Include指令在DbSet(实现OData的OpenSorce项目的一部分)上工作一样 下面的代码表示一个测试用例 Expression<Func<Bar, Bar>> mapBar = b => new Bar { BarInt = b.BarInt, BarString = b.BarString }; Expression<Func<Foo, Foo>> mapF
Expression<Func<Bar, Bar>> mapBar = b => new Bar { BarInt = b.BarInt, BarString = b.BarString };
Expression<Func<Foo, Foo>> mapFoo = f => new Foo { FooInt = f.FooInt, B = null };
Expression<Func<Foo, Foo>> target = f => new Foo { FooInt = f.FooInt,
B = new Bar {
BarInt=f.B.BarInt, BarString = f.B.BarString
} };
但是我不知道如何将表达式newbar{BarInt=b.BarInt,…
,改成newbar{BarInt=f.b.BarInt,…
该函数将需要类似这样的ExpressionVisitor
public class MergingVisitor : ExpressionVisitor
{
private readonly ParameterExpression _oldExpr;
private readonly ParameterExpression _newProp;
private readonly ParameterExpression _newParent;
public MergingVisitor(ParameterExpression oldExpr, ParameterExpression newProp, ParameterExpression newParent)
{
_oldExpr = oldExpr;
_newProp = newProp;
_newParent = newParent;
}
protected override Expression VisitMember(MemberExpression node)
{
if (node.Expression == _oldExpr)
{
/*!!what to do here!!*/
var ma = Expression.MakeMemberAccess(_newProp, node.Member);
return Expression.MakeMemberAccess(_newParent, ma.Member);
}
return base.VisitMember(node);
}
它们都需要用类似的东西连接在一起
public static Expression<Func<T, TMap>> MapNavProperty<T, TMap, U, UMap>(this Expression<Func<T, TMap>> parent, Expression<Func<U, UMap>> nav, string propName)
{
//concern 1 remap name of prop in nav - not sure if I should do this first
var parentInitVarName = parent.Parameters[0].Name;
var parentParam = Expression.Parameter(typeof(T), parentInitVarName);
var propParam = Expression.Parameter(typeof(U), propName);
var mergeVisitor = new MergingVisitor(nav.Parameters[0], propParam, parentParam);
var newNavBody = mergeVisitor.Visit(nav.Body); //as MemberExpression;
//concern 2 replace given property
var visitor = new UpdateExpressionVisitor(propParam, nav.Body);
return (Expression<Func<T, TMap>>)visitor.Visit(parent);
}
公共静态表达式MapNavProperty(此表达式父级、表达式nav、字符串propName)
{
//关注点1在导航中重新映射道具名称-不确定是否应首先执行此操作
var parentInitVarName=parent.Parameters[0].Name;
var parentParam=Expression.Parameter(typeof(T),parentInitVarName);
var propParam=Expression.Parameter(typeof(U),propName);
var mergeVisitor=new MergingVisitor(导航参数[0]、propParam、parentParam);
var newNavBody=mergeVisitor.Visit(nav.Body);//作为成员表达式;
//关注点2替换给定属性
var visitor=新的UpdateExpressionVisitor(propParam,nav.Body);
返回(表达)访客。访问(家长);
}
尽管目前parentParam在表达式中会失败。MakeMemberAccess
函数的类型是T(上例中是Foo),而不是U
如何更改子属性的lamda表达式中的变量名和类型-谢谢
更新
Svick和Ivan Stoev的答案在解释上很博学,而且都很完美——两个答案中(通过的)单元测试和代码都是正确的。非常感谢你们两个——很遗憾我不能勾选两个答案,所以归结到Eeny,meeny,miny,moe
var parentParam = Expression.Parameter(typeof(T), parentInitVarName);
这不起作用,表达式中的参数不是通过名称标识的,而是通过引用标识的。您需要做的只是获取父级的参数
这对我来说没有任何意义。
propName
是属性的名称,因此需要使用它来创建成员访问表达式,而不是参数表达式
您需要的是将一个表达式(
b
)替换为另一个(f.b
)。为此,我将创建:
public class ReplaceVisitor : ExpressionVisitor
{
private readonly Expression _oldExpr;
private readonly Expression _newExpr;
public ReplaceVisitor(Expression oldExpr, Expression newExpr)
{
_oldExpr = oldExpr;
_newExpr = newExpr;
}
public override Expression Visit(Expression node)
{
if (node == _oldExpr)
{
return _newExpr;
}
return base.Visit(node);
}
}
oldExpr
作为参数表达式没有任何意义。您需要的只是一个字符串
您需要在此处实际使用newNavBody
整个MapNavProperty()
现在将如下所示:
var parentParam = parent.Parameters.Single();
var propExpression = Expression.Property(parentParam, propName);
var mergeVisitor = new ReplaceVisitor(nav.Parameters.Single(), propExpression);
var newNavBody = mergeVisitor.Visit(nav.Body);
var visitor = new UpdateExpressionVisitor(propName, newNavBody);
return (Expression<Func<T, TMap>>)visitor.Visit(parent);
public static Expression<Func<T, TMap>> MapNavProperty<T, TMap, U, UMap>(this Expression<Func<T, TMap>> parent, Expression<Func<U, UMap>> nav, string propName)
{
var parameter = parent.Parameters[0];
var body = parent.Body.ReplaceMemberAssignment(
typeof(TMap).GetProperty(propName),
nav.ReplaceParameter(Expression.Property(parameter, propName))
);
return Expression.Lambda<Func<T, TMap>>(body, parameter);
}
var parentParam=parent.Parameters.Single();
var propExpression=Expression.Property(parentParam,propName);
var mergeVisitor=new ReplaceVisitor(nav.Parameters.Single(),propExpression);
var newNavBody=mergeVisitor.Visit(nav.Body);
var visitor=newupdateexpressionvisitor(propName,newNavBody);
返回(表达)访客。访问(家长);
通过这些更改,您的代码将正常工作。我个人会使用不同的帮助程序:
(1) 用于替换参数
static Expression ReplaceParameter(this LambdaExpression lambda, Expression target)
{
return lambda.Body.ReplaceParameter(lambda.Parameters.Single(), target);
}
static Expression ReplaceParameter(this Expression expression, ParameterExpression source, Expression target)
{
return new ParameterReplacer { Source = source, Target = target }.Visit(expression);
}
class ParameterReplacer : ExpressionVisitor
{
public ParameterExpression Source;
public Expression Target;
protected override Expression VisitParameter(ParameterExpression node)
{
return node == Source ? Target : base.VisitParameter(node);
}
}
(2) 用于替换成员分配值
static Expression ReplaceMemberAssignment(this Expression expression, MemberInfo member, Expression value)
{
return new MemberAssignmentReplacer { Member = member, Value = value }.Visit(expression);
}
class MemberAssignmentReplacer : ExpressionVisitor
{
public MemberInfo Member;
public Expression Value;
protected override MemberAssignment VisitMemberAssignment(MemberAssignment node)
{
return node.Member == Member ? node.Update(Value) : base.VisitMemberAssignment(node);
}
}
有了这些助手,所讨论的功能如下:
var parentParam = parent.Parameters.Single();
var propExpression = Expression.Property(parentParam, propName);
var mergeVisitor = new ReplaceVisitor(nav.Parameters.Single(), propExpression);
var newNavBody = mergeVisitor.Visit(nav.Body);
var visitor = new UpdateExpressionVisitor(propName, newNavBody);
return (Expression<Func<T, TMap>>)visitor.Visit(parent);
public static Expression<Func<T, TMap>> MapNavProperty<T, TMap, U, UMap>(this Expression<Func<T, TMap>> parent, Expression<Func<U, UMap>> nav, string propName)
{
var parameter = parent.Parameters[0];
var body = parent.Body.ReplaceMemberAssignment(
typeof(TMap).GetProperty(propName),
nav.ReplaceParameter(Expression.Property(parameter, propName))
);
return Expression.Lambda<Func<T, TMap>>(body, parameter);
}
公共静态表达式MapNavProperty(此表达式父级、表达式nav、字符串propName)
{
var参数=父参数[0];
var body=parent.body.ReplaceMemberAssignment(
typeof(TMap).GetProperty(propName),
ReplaceParameter(Expression.Property(参数,propName))
);
返回表达式.Lambda(主体,参数);
}
static Expression ReplaceParameter(this LambdaExpression lambda, Expression target)
{
return lambda.Body.ReplaceParameter(lambda.Parameters.Single(), target);
}
static Expression ReplaceParameter(this Expression expression, ParameterExpression source, Expression target)
{
return new ParameterReplacer { Source = source, Target = target }.Visit(expression);
}
class ParameterReplacer : ExpressionVisitor
{
public ParameterExpression Source;
public Expression Target;
protected override Expression VisitParameter(ParameterExpression node)
{
return node == Source ? Target : base.VisitParameter(node);
}
}
static Expression ReplaceMemberAssignment(this Expression expression, MemberInfo member, Expression value)
{
return new MemberAssignmentReplacer { Member = member, Value = value }.Visit(expression);
}
class MemberAssignmentReplacer : ExpressionVisitor
{
public MemberInfo Member;
public Expression Value;
protected override MemberAssignment VisitMemberAssignment(MemberAssignment node)
{
return node.Member == Member ? node.Update(Value) : base.VisitMemberAssignment(node);
}
}
public static Expression<Func<T, TMap>> MapNavProperty<T, TMap, U, UMap>(this Expression<Func<T, TMap>> parent, Expression<Func<U, UMap>> nav, string propName)
{
var parameter = parent.Parameters[0];
var body = parent.Body.ReplaceMemberAssignment(
typeof(TMap).GetProperty(propName),
nav.ReplaceParameter(Expression.Property(parameter, propName))
);
return Expression.Lambda<Func<T, TMap>>(body, parameter);
}