C# 将包含转换为表达式树
有关:C# 将包含转换为表达式树,c#,linq,lambda,expression-trees,c#-6.0,C#,Linq,Lambda,Expression Trees,C# 6.0,有关: 请考虑此代码: from a in myTbl where a.Address.Contains(strToCheck) select a 如何将其转换为表达式树并使用表达式编写上述代码? 主要问题是将a.Address.Contains(strToCheck)转换为表达式树 编辑1)地址是一个字符串字段,strotcheck是一个字符串 谢谢你没有指定myTbl的类型, 因此,我仅使用对象列表创建了一个简单的解决方案。 using System; using System.Linq;
请考虑此代码:
from a in myTbl
where a.Address.Contains(strToCheck)
select a
如何将其转换为表达式树并使用表达式编写上述代码?
主要问题是将a.Address.Contains(strToCheck)
转换为表达式树
编辑1)地址是一个字符串
字段,strotcheck
是一个字符串
谢谢你没有指定myTbl的类型,
因此,我仅使用对象列表创建了一个简单的解决方案。
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Collections.Generic;
namespace Test
{
class Program
{
static void Main(string[] args) {
var adresses = FilterByAddress("Address", new List<Person> { new Person { Address = "Address1" }, new Person { Address = "AAAAAA" } });
}
public static IEnumerable<Person> FilterByAddress(string strToCheck, List<Person> list) {
var listParam = Expression.Parameter(typeof(IEnumerable<Person>), "list");
Expression<Func<Person, bool>> contains = a => a.Address.Contains(strToCheck);
var select = typeof(Enumerable).GetMethods().Single(m => m.Name.Equals("Where") && m.GetParameters()[1].ParameterType.GetGenericArguments().Length == 2);
var genericMethod = select.MakeGenericMethod(new[] { typeof(Person) });
var call = Expression.Call(null, genericMethod, new Expression[] { listParam, contains });
var lambda = Expression.Lambda<Func<IEnumerable<Person>, IEnumerable<Person>>>(call, new[] { listParam });
return lambda.Compile().Invoke(list);
}
}
public class Person
{
public string Address { get; set; }
}
}
使用系统;
使用System.Linq;
使用System.Linq.Expressions;
使用System.Collections.Generic;
名称空间测试
{
班级计划
{
静态void Main(字符串[]参数){
var Address=FilterByAddress(“地址”,新列表{new Person{Address=“Address1”},new Person{Address=“AAAAAA”});
}
公共静态IEnumerable FilterByAddress(字符串strToCheck,列表){
var listParam=Expression.Parameter(typeof(IEnumerable),“list”);
表达式contains=a=>a.Address.contains(strToCheck);
var select=typeof(Enumerable).GetMethods().Single(m=>m.Name.Equals(“Where”)&&m.GetParameters()[1]。ParameterType.GetGenericArguments().Length==2);
var genericMethod=select.MakeGenericMethod(new[]{typeof(Person)});
var call=Expression.call(null,genericMethod,新表达式[]{listParam,contains});
var lambda=Expression.lambda(调用,new[]{listParam});
返回lambda.Compile().Invoke(列表);
}
}
公共阶层人士
{
公共字符串地址{get;set;}
}
}
如果要使用“按谓词筛选”,可以将expression
作为参数传递(一行)
static void Main(字符串[]args){
var strToCheck=“地址”;
var list=newlist{newperson{Address=“Address1”},newperson{Address=“AAAAAA”};
var Address=FilterByAddress(list,p=>p.Address.Contains(strToCheck));
}
公共静态IEnumerable FilterByAddress(列表、表达式谓词){
var listParam=Expression.Parameter(typeof(IEnumerable),“list”);
var select=typeof(Enumerable).GetMethods().Single(m=>m.Name.Equals(“Where”)&&m.GetParameters()[1]。ParameterType.GetGenericArguments().Length==2);
var genericMethod=select.MakeGenericMethod(new[]{typeof(Person)});
var call=Expression.call(null,genericMethod,新表达式[]{listParam,predicateEx});
var lambda=Expression.lambda(调用,new[]{listParam});
返回lambda.Compile().Invoke(列表);
}
如果您有一个非常复杂的谓词,它跨越多行(表达式树可以从一行lambda计算),您可以使用以下技巧从谓词Func构造表达式树:
static void Main(string[] args) {
var strToCheck = "Address";
Func<Person, bool> predicate = p => {
return p.Address.Contains(strToCheck);
};
var list = new List<Person> { new Person { Address = "Address1" }, new Person { Address = "AAAAAA" } };
var adresses = FilterByAddress(list, predicate);
}
public static IEnumerable<Person> FilterByAddress(List<Person> list, Func<Person, bool> predicate) {
var listParam = Expression.Parameter(typeof(IEnumerable<Person>), "list");
Expression<Func<Person, bool>> predicateEx = p => predicate(p);
var select = typeof(Enumerable).GetMethods().Single(m => m.Name.Equals("Where") && m.GetParameters()[1].ParameterType.GetGenericArguments().Length == 2);
var genericMethod = select.MakeGenericMethod(new[] { typeof(Person) });
var call = Expression.Call(null, genericMethod, new Expression[] { listParam, predicateEx });
var lambda = Expression.Lambda<Func<IEnumerable<Person>, IEnumerable<Person>>>(call, new[] { listParam });
return lambda.Compile().Invoke(list);
}
static void Main(字符串[]args){
var strToCheck=“地址”;
Func谓词=p=>{
返回p.Address.Contains(strToCheck);
};
var list=newlist{newperson{Address=“Address1”},newperson{Address=“AAAAAA”};
var address=FilterByAddress(列表,谓词);
}
公共静态IEnumerable FilterByAddress(列表,Func谓词){
var listParam=Expression.Parameter(typeof(IEnumerable),“list”);
表达式predicateEx=p=>predicate(p);
var select=typeof(Enumerable).GetMethods().Single(m=>m.Name.Equals(“Where”)&&m.GetParameters()[1]。ParameterType.GetGenericArguments().Length==2);
var genericMethod=select.MakeGenericMethod(new[]{typeof(Person)});
var call=Expression.call(null,genericMethod,新表达式[]{listParam,predicateEx});
var lambda=Expression.lambda(调用,new[]{listParam});
返回lambda.Compile().Invoke(列表);
}
使用泛型方法按谓词筛选列表
static void Main(string[] args) {
var strToCheck = "Address";
Func<Person, bool> predicate = p => {
return p.Address.Contains(strToCheck);
};
var list = new List<Person> { new Person { Address = "Address1" }, new Person { Address = "AAAAAA" } };
var adresses = FilterBy<Person>(list, predicate);
}
public static IEnumerable<T> FilterBy<T>(List<T> list, Func<T, bool> predicate) {
var listParam = Expression.Parameter(typeof(IEnumerable<T>), "list");
Expression<Func<T, bool>> predicateEx = p => predicate(p);
var select = typeof(Enumerable).GetMethods().Single(m => m.Name.Equals("Where") && m.GetParameters()[1].ParameterType.GetGenericArguments().Length == 2);
var genericMethod = select.MakeGenericMethod(new[] { typeof(T) });
var call = Expression.Call(null, genericMethod, new Expression[] { listParam, predicateEx });
var lambda = Expression.Lambda<Func<IEnumerable<T>, IEnumerable<T>>>(call, new[] { listParam });
return lambda.Compile().Invoke(list);
}
}
static void Main(字符串[]args){
var strToCheck=“地址”;
Func谓词=p=>{
返回p.Address.Contains(strToCheck);
};
var list=newlist{newperson{Address=“Address1”},newperson{Address=“AAAAAA”};
var address=FilterBy(列表,谓词);
}
公共静态IEnumerable筛选器by(列表,Func谓词){
var listParam=Expression.Parameter(typeof(IEnumerable),“list”);
表达式predicateEx=p=>predicate(p);
var select=typeof(Enumerable).GetMethods().Single(m=>m.Name.Equals(“Where”)&&m.GetParameters()[1]。ParameterType.GetGenericArguments().Length==2);
var genericMethod=select.MakeGenericMethod(new[]{typeof(T)});
var call=Expression.call(null,genericMethod,新表达式[]{listParam,predicateEx});
var lambda=Expression.lambda(调用,new[]{listParam});
返回lambda.Compile().Invoke(列表);
}
}
您没有指定myTbl的类型,因此,我仅使用对象列表创建了一个简单的解决方案。
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Collections.Generic;
namespace Test
{
class Program
{
static void Main(string[] args) {
var adresses = FilterByAddress("Address", new List<Person> { new Person { Address = "Address1" }, new Person { Address = "AAAAAA" } });
}
public static IEnumerable<Person> FilterByAddress(string strToCheck, List<Person> list) {
var listParam = Expression.Parameter(typeof(IEnumerable<Person>), "list");
Expression<Func<Person, bool>> contains = a => a.Address.Contains(strToCheck);
var select = typeof(Enumerable).GetMethods().Single(m => m.Name.Equals("Where") && m.GetParameters()[1].ParameterType.GetGenericArguments().Length == 2);
var genericMethod = select.MakeGenericMethod(new[] { typeof(Person) });
var call = Expression.Call(null, genericMethod, new Expression[] { listParam, contains });
var lambda = Expression.Lambda<Func<IEnumerable<Person>, IEnumerable<Person>>>(call, new[] { listParam });
return lambda.Compile().Invoke(list);
}
}
public class Person
{
public string Address { get; set; }
}
}
使用系统;
使用System.Linq;
使用System.Linq.Expressions;
使用System.Collections.Generic;
名称空间测试
{
班级计划
{
静态void Main(字符串[]参数){
var Address=FilterByAddress(“地址”,新列表{new Person{Address=“Address1”},new Person{Address=“AAAAAA”});
}
公共静态IEnumerable FilterByAddress(字符串strToCheck,列表){
var listParam=Expression.Parameter(typeof(IEnumerable),“list”);
表达式contains=a=>a.Address.contains(strToCheck);
var select=typeof(Enumerable).GetMethods().Single(m=>m.Name.Equals(“Where”)&&m.GetParameters()[1]。ParameterType.GetGenericArguments().Length==2);
var genericMethod=select.MakeGenericMethod(new[]{typeof(Person)});
var call=Expr
public static MethodCallExpression Call(
Expression instance,
string methodName,
Type[] typeArguments,
params Expression[] arguments
)
var body = Expression.Call(
Expression.PropertyOrField(param, "Address"), // instance
"Contains", // method
Type.EmptyTypes, // no generic type arguments
Expression.Constant(strToCheck) // argument
);