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

效果：

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

構(gòu)建表達(dá)式樹：（快速式）

1.添加命名空間：

using System.Linq.Expressions;

2.聲明參數(shù)表達(dá)式（比如Book實(shí)體）

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

3.

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

4.通過反射機(jī)制調(diào)用string.Contains,構(gòu)建like;

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

5.拼接

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

//exp:and前面的語句，拼接之前的語句；

//Expression.Call():方法調(diào)用表達(dá)式；

//Expression.Property(param, "Name")字段或?qū)傩员磉_(dá)式

//methodinfo:調(diào)用上面Contains方法；

//Expression.Constant(s1):常量表達(dá)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(dá)式

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

7.調(diào)用

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

?

------------------------------------------------------------詳細(xì)（轉(zhuǎn)述網(wǎng)友秦迷）

//---------------動(dòng)態(tài)創(chuàng)建表達(dá)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(chuàng)建需要查找的參數(shù)

?

//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(shí)現(xiàn)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(dá)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(cuò)信息：

???????????????????? * 沒有為類型“System.Boolean”和“System.Boolean”定義二進(jìn)制運(yùn)算符 Add。

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

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

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

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

//生成Lambda表達(dá)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(jié)果：

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

*/

EF4.0、4.3創(chuàng)建表達(dá)式樹狀動(dòng)態(tài)查詢總結(jié)