Expression<Func<int, int, bool>> expression = (x, y) => x!=0 && x==y+1;

//动态创建表达式树
Expression<Func<int, int, bool>> expression = (x, y) => x != 0 && x == y + 1;//先创建两个参数
ParameterExpression[] parameters = new ParameterExpression[] { Expression.Parameter(typeof(int),"x"), Expression.Parameter(typeof(int), "y") };ParameterExpression param1 = parameters[0];
ParameterExpression param2 = parameters[1];//下面先创建右边第一个表达式 x!=0
//(1)常量 0x
ConstantExpression rightLeftRight = Expression.Constant(0, typeof(int));
//(2)创建左边第一个表达式 x!=0
BinaryExpression rightLeft = Expression.NotEqual(param1, rightLeftRight);//下面创建右边第二个表达式 x==y+1
//(3) 先创建右边部分表达式y+1
BinaryExpression rightRightRight = Expression.Add(param2, Expression.Constant(1, typeof(int)));
//(4)创建右边表达式  x==y+1
BinaryExpression rightRight = Expression.Equal(param1, rightRightRight);//5）创建表达式 右部整体 x != 0 && x == y + 1
BinaryExpression Right = Expression.AndAlso(rightLeft, rightRight);//(6)完成整个表达式
Expression<Func<int, int, bool>> lambdaExr = Expression.Lambda<Func<int, int, bool>>(Right,parameters);Console.Write(lambdaExr.ToString());

//执行表达式树
Expression<Func<int, int, bool>> expression = (x, y) => x != 0 && x == y + 1;
Func<int, int, bool> result = expression.Compile();
bool result2= expression.Compile()(9,8);
Console.WriteLine(result2);
Console.WriteLine(result(3, 2));
Console.WriteLine(result(5, 4));
Console.WriteLine(result(6, 4));
Console.WriteLine(result(-6, -7));

public class OrElseModifier : ExpressionVisitor
{public Expression Modify(Expression expression){return Visit(expression);}protected override Expression VisitBinary(BinaryExpression b){if (b.NodeType == ExpressionType.AndAlso){Expression left = this.Visit(b.Left);Expression right = this.Visit(b.Right);return Expression.MakeBinary(ExpressionType.OrElse, left, right, b.IsLiftedToNull, b.Method);}return base.VisitBinary(b);}
}

//修改表达式树
Expression<Func<int, int, bool>> expression = (x, y) => x != 0 && x == y + 1;OrElseModifier amf = new OrElseModifier();
Expression newExp= amf.Modify(expression);
Console.WriteLine("原表达式：      "+ expression.ToString());
Console.WriteLine("修改后的表达式："+newExp.ToString());

/// <summary
/// 我的博客文章实体类
/// </summary>
public class MyArticle
{/// <summary>/// 文章编号/// </summary>public int id { get; set; }/// <summary>/// 文章标题/// </summary>public string title { get; set; }/// <summary>/// 文章摘要/// </summary>public string summary { get; set; }/// <summary>/// 发布时间/// </summary>public DateTime published { get; set; }/// <summary>/// 最后更新时间/// </summary>public DateTime updated { get; set; }/// <summary>/// URL地址/// </summary>public string link { get; set; }/// <summary>/// 推荐数/// </summary>public int diggs { get; set; }/// <summary>/// 浏览量/// </summary>public int views { get; set; }/// <summary>/// 评论数/// </summary>public int comments { get; set; }/// <summary>/// 作者/// </summary>public string author { get; set; }
}

//动态查询 我在博客园中的文章分类查询//第一步，获取我在博客园中的文章
List<MyArticle> myArticleList = new List<MyArticle>();
var document = XDocument.Load("http://wcf.open.cnblogs.com/blog/u/yubinfeng/posts/1/100");var elements = document.Root.Elements();//在进行这个工作之前，我们先获取我博客中的文章列表
var result = elements.Where(m => m.Name.LocalName == "entry").Select(myArticle => new MyArticle
{id = Convert.ToInt32(myArticle.Elements().SingleOrDefault(x => x.Name.LocalName == "id").Value),title = myArticle.Elements().SingleOrDefault(x => x.Name.LocalName == "title").Value,published = Convert.ToDateTime(myArticle.Elements().SingleOrDefault(x => x.Name.LocalName == "published").Value),updated = Convert.ToDateTime(myArticle.Elements().SingleOrDefault(x => x.Name.LocalName == "updated").Value),diggs = Convert.ToInt32(myArticle.Elements().SingleOrDefault(x => x.Name.LocalName == "diggs").Value),views = Convert.ToInt32(myArticle.Elements().SingleOrDefault(x => x.Name.LocalName == "views").Value),comments = Convert.ToInt32(myArticle.Elements().SingleOrDefault(x => x.Name.LocalName == "comments").Value),summary = myArticle.Elements().SingleOrDefault(x => x.Name.LocalName == "summary").Value,link = myArticle.Elements().SingleOrDefault(x => x.Name.LocalName == "link").Attribute("href").Value,author = myArticle.Elements().SingleOrDefault(x => x.Name.LocalName == "author").Elements().SingleOrDefault(x => x.Name.LocalName == "name").Value
});
myArticleList.AddRange(result);

public static IQueryable<T> MySearchList(IQueryable<T> myArticleTable, T myArticle)
{//第二步，动态查询我的文章// List<MyArticle> SearchMyArticleList = new List<MyArticle>();//1.我们先定义几个查询的参数(文章标题,浏览数,发布时间)
ParameterExpression myart = Expression.Parameter(typeof(T), "article");   //标题     ParameterExpression searchTitle = Expression.Parameter(typeof(string), "searchTitle");   //标题     ParameterExpression searchViews = Expression.Parameter(typeof(int), "searchViews");     //浏览数   ParameterExpression searchPublished = Expression.Parameter(typeof(DateTime), "searchPublished");//创建月份//2.使用表达式树，动态生成查询 （查询某个日期的文章）Expression left = Expression.Property(myart, typeof(T).GetProperty("published")); //访问属性的表达式Expression right = Expression.Property(Expression.Constant(myArticle), typeof(T).GetProperty("published"));//访问属性的表达式Expression e1 = Expression.GreaterThanOrEqual(left, right); //大于等于//2.使用表达式树，动态生成查询 （按点击数查询）Expression left2 = Expression.Property(myart, typeof(T).GetProperty("views")); //访问属性的表达式Expression right2 = Expression.Property(Expression.Constant(myArticle), typeof(T).GetProperty("views"));//访问属性的表达式Expression e2 = Expression.GreaterThanOrEqual(left2, right2);//3.构造动态查询 （按点击数和月份查询）Expression predicateBody = Expression.AndAlso(e1, e2);//4.构造过滤MethodCallExpression whereCallExpression = Expression.Call(typeof(Queryable),"Where",new Type[] { typeof(T) },myArticleTable.Expression,Expression.Lambda<Func<T, bool>>(predicateBody, new ParameterExpression[] { myart }));//构造排序MethodCallExpression orderByCallExpression = Expression.Call(typeof(Queryable),"OrderByDescending",new Type[] { typeof(T), typeof(int) },whereCallExpression,Expression.Lambda<Func<T, int>>(left2, new ParameterExpression[] { myart }));//创建查询表达式树IQueryable<T> results = myArticleTable.Provider.CreateQuery<T>(orderByCallExpression);return results;
}

IQueryable<MyArticle> results = ExpressionTree<MyArticle>.MySearchList(myArticleList.AsQueryable<MyArticle>(), new MyArticle() { views=500, published=Convert.ToDateTime("2015-06")});foreach (MyArticle article in results)Console.WriteLine(article.title + " \n [发布日期:"+article.published+"] [浏览数："+article.views+"]");