Linq表达式树

Code

   
     using System;
using System.Linq.Expressions;
using System.Linq;
using System.Data.Linq;
namespace KingRi.Test
{
 public class Student
 {
 public Student(string name)
 {
 this.name = name;
 }
 private string name;
 public string Name
 {
 get
 {
 return this.name;
 }
 set
 {
 this.name = value;
 }
 }
 }
 public class Client
 {
 static void Main()
 {
 //表达式树基础
 /*
 //Expression<Func<int, int, int>> expression = (a, b)=>a*b+2
 ParameterExpression leftParam = Expression.Parameter(typeof(int), "a");
 ParameterExpression rightParam = Expression.Parameter(typeof(int), "b");

 BinaryExpression binaryLeft = Expression.Multiply(leftParam, rightParam);
 ConstantExpression conRight = Expression.Constant(2, typeof(int));

 BinaryExpression binaryBody = Expression.Add(binaryLeft, conRight);
 LambdaExpression lambda = Expression.Lambda<Func<int, int, int>>(binaryBody, leftParam, rightParam);
 Console.WriteLine(lambda.ToString());
 */

 //动态构建Linq
 /*
 ParameterExpression c1= Expression.Parameter(typeof(Student), "std");
 Expression condition = Expression.Constant(false);

 string[] cs = {"ad", "ac"};
 foreach (string c in cs)
 {
 Expression con = Expression.Call(
 Expression.Property(c1, typeof(Student).GetProperty("Name")),
 typeof(string).GetMethod("StartsWith", new Type[] { typeof(string) }),
 Expression.Constant(c));
 condition = Expression.Or(con, condition);
 }
 Expression<Func<Student, bool>> end =
 Expression.Lambda<Func<Student, bool>>(condition, new ParameterExpression[] { c1 });
 Console.WriteLine(end.ToString());
 */

 //Expression.Call方法学习
 Student[] stds = {
 new Student("ac Zhang"),
 new Student("ad Lisi"),
 new Student("aa WangWu")
 };
 ParameterExpression param = Expression.Parameter(typeof(Student), "c");
 Expression seletor = Expression.Property(param, typeof(Student).GetProperty("Name"));
 Expression pred = Expression.Lambda(seletor, param);

 Expression expr = Expression.Call(
 typeof(Queryable),
 "Select",
 new Type[] { typeof(Queryable), typeof(Expression<>) },
 Expression.Constant(stds), 
 pred);
 //(null, ((MethodInfo) MethodBase.GetCurrentMethod()).MakeGenericMethod(new Type[] { typeof(TSource) }), new Expression[] { source.Expression, Expression.Quote(predicate) }));
 IQueryable<string> query = stds.AsQueryable().Provider.CreateQuery<string>(expr);
 DataContext db = new DataContext("");
 
 System.Data.Common.DbCommand cmd = db.GetCommand(query);
 Console.WriteLine(cmd.CommandText);
 }
 }
}