我尝试了简单(不完整)的实现来改变表达式
p => p.Id == 15
(代码如下)。有一个名为“crossmapping”的类定义了原始类型和“新”类型以及类型成员之间的映射。
有好几种方法
Mutate_XY_Expression
对于每个表达式类型,这将生成新的变异表达式。方法输入需要原始表达式(
MemberExpression originalExpression
)作为表达式的模型,列表或参数表达式(
IList<ParameterExpression> parameterExpressions
)它们是由“parent”表达式定义的参数,应该由“parent”主体和映射对象使用(
CrossMapping mapping
)它定义类型和成员之间的映射。
对于完整的实现,您可能需要从父表达式获得比参数更多的信息。但模式应该是一样的。
sample并没有实现visitor模式,正如您所知——这是因为它很简单。但是没有任何障碍可以转化为他们。
我希望,这会有帮助。
代码(C 4.0):
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Linq.Expressions;
namespace ConsoleApplication1 {
public class Product1 {
public int Id { get; set; }
public string Name { get; set; }
public decimal Weight { get; set; }
}
public class Product2 {
public int Id { get; set; }
public string Name { get; set; }
public decimal Weight { get; set; }
}
class Program {
static void Main( string[] args ) {
// list of products typed as Product1
var lst1 = new List<Product1> {
new Product1{ Id = 1, Name = "One" },
new Product1{ Id = 15, Name = "Fifteen" },
new Product1{ Id = 9, Name = "Nine" }
};
// the expression for filtering products
// typed as Product1
Expression<Func<Product1, bool>> q1;
q1 = p => p.Id == 15;
// list of products typed as Product2
var lst2 = new List<Product2> {
new Product2{ Id = 1, Name = "One" },
new Product2{ Id = 15, Name = "Fifteen" },
new Product2{ Id = 9, Name = "Nine" }
};
// type of Product1
var tp1 = typeof( Product1 );
// property info of "Id" property from type Product1
var tp1Id = tp1.GetProperty( "Id", BindingFlags.Public | BindingFlags.Instance );
// delegate type for predicating for Product1
var tp1FuncBool = typeof( Func<,> ).MakeGenericType( tp1, typeof( bool ) );
// type of Product2
var tp2 = typeof( Product2 );
// property info of "Id" property from type Product2
var tp21Id = tp2.GetProperty( "Id", BindingFlags.Public | BindingFlags.Instance );
// delegate type for predicating for Product2
var tp2FuncBool = typeof( Func<,> ).MakeGenericType( tp2, typeof( bool ) );
// mapping object for types and type members
var cm1 = new CrossMapping {
TypeMapping = {
// Product1 -> Product2
{ tp1, tp2 },
// Func<Product1, bool> -> Func<Product2, bool>
{ tp1FuncBool, tp2FuncBool }
},
MemberMapping = {
// Product1.Id -> Product2.Id
{ tp1Id, tp21Id }
}
};
// mutate express from Product1's "enviroment" to Product2's "enviroment"
var cq1_2 = MutateExpression( q1, cm1 );
// compile lambda to delegate
var dlg1_2 = ((LambdaExpression)cq1_2).Compile();
// executing delegate
var rslt1_2 = lst2.Where( (Func<Product2, bool>)dlg1_2 ).ToList();
return;
}
class CrossMapping {
public IDictionary<Type, Type> TypeMapping { get; private set; }
public IDictionary<MemberInfo, MemberInfo> MemberMapping { get; private set; }
public CrossMapping() {
this.TypeMapping = new Dictionary<Type, Type>();
this.MemberMapping = new Dictionary<MemberInfo, MemberInfo>();
}
}
static Expression MutateExpression( Expression originalExpression, CrossMapping mapping ) {
var ret = MutateExpression(
originalExpression: originalExpression,
parameterExpressions: null,
mapping: mapping
);
return ret;
}
static Expression MutateExpression( Expression originalExpression, IList<ParameterExpression> parameterExpressions, CrossMapping mapping ) {
Expression ret;
if ( null == originalExpression ) {
ret = null;
}
else if ( originalExpression is LambdaExpression ) {
ret = MutateLambdaExpression( (LambdaExpression)originalExpression, parameterExpressions, mapping );
}
else if ( originalExpression is BinaryExpression ) {
ret = MutateBinaryExpression( (BinaryExpression)originalExpression, parameterExpressions, mapping );
}
else if ( originalExpression is ParameterExpression ) {
ret = MutateParameterExpression( (ParameterExpression)originalExpression, parameterExpressions, mapping );
}
else if ( originalExpression is MemberExpression ) {
ret = MutateMemberExpression( (MemberExpression)originalExpression, parameterExpressions, mapping );
}
else if ( originalExpression is ConstantExpression ) {
ret = MutateConstantExpression( (ConstantExpression)originalExpression, parameterExpressions, mapping );
}
else {
throw new NotImplementedException();
}
return ret;
}
static Type MutateType( Type originalType, IDictionary<Type, Type> typeMapping ) {
if ( null == originalType ) { return null; }
Type ret;
typeMapping.TryGetValue( originalType, out ret );
if ( null == ret ) { ret = originalType; }
return ret;
}
static MemberInfo MutateMember( MemberInfo originalMember, IDictionary<MemberInfo, MemberInfo> memberMapping ) {
if ( null == originalMember ) { return null; }
MemberInfo ret;
memberMapping.TryGetValue( originalMember, out ret );
if ( null == ret ) { ret = originalMember; }
return ret;
}
static LambdaExpression MutateLambdaExpression( LambdaExpression originalExpression, IList<ParameterExpression> parameterExpressions, CrossMapping mapping ) {
if ( null == originalExpression ) { return null; }
var newParameters = (from p in originalExpression.Parameters
let np = MutateParameterExpression( p, parameterExpressions, mapping )
select np).ToArray();
var newBody = MutateExpression( originalExpression.Body, newParameters, mapping );
var newType = MutateType( originalExpression.Type, mapping.TypeMapping );
var ret = Expression.Lambda(
delegateType: newType,
body: newBody,
name: originalExpression.Name,
tailCall: originalExpression.TailCall,
parameters: newParameters
);
return ret;
}
static BinaryExpression MutateBinaryExpression( BinaryExpression originalExpression, IList<ParameterExpression> parameterExpressions, CrossMapping mapping ) {
if ( null == originalExpression ) { return null; }
var newExprConversion = MutateExpression( originalExpression.Conversion, parameterExpressions, mapping );
var newExprLambdaConversion = (LambdaExpression)newExprConversion;
var newExprLeft = MutateExpression( originalExpression.Left, parameterExpressions, mapping );
var newExprRigth = MutateExpression( originalExpression.Right, parameterExpressions, mapping );
var newType = MutateType( originalExpression.Type, mapping.TypeMapping );
var newMember = MutateMember( originalExpression.Method, mapping.MemberMapping);
var newMethod = (MethodInfo)newMember;
var ret = Expression.MakeBinary(
binaryType: originalExpression.NodeType,
left: newExprLeft,
right: newExprRigth,
liftToNull: originalExpression.IsLiftedToNull,
method: newMethod,
conversion: newExprLambdaConversion
);
return ret;
}
static ParameterExpression MutateParameterExpression( ParameterExpression originalExpresion, IList<ParameterExpression> parameterExpressions, CrossMapping mapping ) {
if ( null == originalExpresion ) { return null; }
ParameterExpression ret = null;
if ( null != parameterExpressions ) {
ret = (from p in parameterExpressions
where p.Name == originalExpresion.Name
select p).FirstOrDefault();
}
if ( null == ret ) {
var newType = MutateType( originalExpresion.Type, mapping.TypeMapping );
ret = Expression.Parameter( newType, originalExpresion.Name );
}
return ret;
}
static MemberExpression MutateMemberExpression( MemberExpression originalExpression, IList<ParameterExpression> parameterExpressions, CrossMapping mapping ) {
if ( null == originalExpression ) { return null; }
var newExpression = MutateExpression( originalExpression.Expression, parameterExpressions, mapping );
var newMember = MutateMember( originalExpression.Member, mapping.MemberMapping );
var ret = Expression.MakeMemberAccess(
expression: newExpression,
member: newMember
);
return ret;
}
static ConstantExpression MutateConstantExpression( ConstantExpression originalExpression, IList<ParameterExpression> parameterExpressions, CrossMapping mapping ) {
if ( null == originalExpression ) { return null; }
var newType = MutateType( originalExpression.Type, mapping.TypeMapping );
var newValue = originalExpression.Value;
var ret = Expression.Constant(
value: newValue,
type: newType
);
return ret;
}
}
}
