---------------------------------------------快速適用

效果：

where name like '%王%' and Age>=35 or Age<10

構建表達式樹：（快速式）

1.添加命名空間：

using System.Linq.Expressions;

2.聲明參數表達式（比如Book實體）

?ParameterExpression param = Expression.Parameter(typeof(Book));

3.

Expression exp = Expression.Constant(true);初始化表達式樹；

4.通過反射機制調用string.Contains,構建like;

var methodinfo = typeof(string).GetMethod("Contains");

5.拼接

//Expression.And:表示 and 后面的條件當然還有Or、 >=、<=、=等

//exp:and前面的語句，拼接之前的語句；

//Expression.Call():方法調用表達式；

//Expression.Property(param, "Name")字段或屬性表達式

//methodinfo:調用上面Contains方法；

//Expression.Constant(s1):常量表達式；s1=“王”；

exp = Expression.And(exp, Expression.Call(Expression.Property(param, "Name"),methodinfo, Expression.Constant(s1)));

exp = Expression.And(exp, Expression.GreaterThanOrEqual(Expression.Property(param, "Id"),Expression.Constant(35)));

exp = Expression.Or(exp, Expression.LessThan(Expression.Property(param, "Id"), Expression.Constant(10)));

6.描述lambda表達式

var lam = Expression.Lambda<Func<Book, bool>>(exp, param);

7.調用

var lis = books.Where<Book>(lam).ToList();

?

------------------------------------------------------------詳細（轉述網友秦迷）

//---------------動態創建表達式目錄樹---------------//

//名字模糊查詢tony

//年齡大于等于20

//年齡小于30

string uname = "tony";

List<Expression> expList = new List<Expression>(2);

ParameterExpression parExp = Expression.Parameter(typeof(UserInfo), "infos");//創建需要查找的參數

?

//查姓名infos.UserName.Contains("tony")

MemberExpression unameExp = Expression.Property(parExp, "UserName");

MethodInfo containsMethod = typeof(string).GetMethod("Contains");//using System.Reflection;指定實現Contains方法

ConstantExpression unamevalueExp = Expression.Constant(uname, typeof(string));

MethodCallExpression containsExp = Expression.Call(unameExp, containsMethod, unamevalueExp);

expList.Add(containsExp);

?

//查年齡infos.Age>=20

MemberExpression age1 = Expression.Property(parExp, "Age");

ConstantExpression agevalue1 = Expression.Constant(20, typeof(int));

BinaryExpression gteExp = Expression.GreaterThanOrEqual(age1, agevalue1);

expList.Add(gteExp);

//查年齡infos.Age<30

//if (1 > 2)

//{

MemberExpression age2 = Expression.Property(parExp, "Age");

ConstantExpression agevalue2 = Expression.Constant(30, typeof(int));

BinaryExpression ltExp = Expression.LessThan(age2, agevalue2);

expList.Add(ltExp);

//}

?

?

//把上面的表達式連接起來

Expression whereExp = null;

foreach (var item in expList)

??? {

??????? if (whereExp == null)

??????????????? {

??????????????????? whereExp = item;

??????????????? }

??????????????? else

??????????????? {

??????????????????? whereExp = Expression.And(whereExp, item);

??????????????????? /*

???????????????????? * 出錯信息：

???????????????????? * 沒有為類型“System.Boolean”和“System.Boolean”定義二進制運算符 Add。

???????????????????? * 是And，開始我寫錯成了Add一直找不到原因

??????????????????? ?*/

??????????????? }

??????????? }

//生成Lambda表達式

//Expression<Func<UserInfo, bool>> lambda = Expression.Lambda<Func<UserInfo, bool>>(whereExp, parExp);

LambdaExpression lambda = Expression.Lambda<Func<UserInfo, bool>>(whereExp, parExp);

Console.WriteLine(lambda);

/*

* 生成結果：

* infos => ((infos.UserName.Contains("tony") And (infos.Age>=20)) And (infos.Age<30))

*/

EF4.0、4.3創建表達式樹狀動態查詢總結