ConstantExpression exp1 = Expression.Constant(1);构建常量表达式（还可以加类型）
BinaryExpression exp12 = Expression.Add(exp1, exp2);构建二元加法表达式，参数为左右两个需要相加的常量表达式或者变量
ParameterExpression expA = Expression.Parameter(typeof(double), "a");构建参数
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ParameterExpression expA = Expression.Parameter(typeof(double), "a"); //参数a
MethodCallExpression expCall = Expression.Call(null,
typeof(Math).GetMethod("Sin", BindingFlags.Static | BindingFlags.Public),
expA); //Math.Sin(a)构建方法调用表达式（表示一次方法调用）
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LambdaExpression exp = Expression.Lambda(expCall, expA); //构建lambda表达式（由表达式体和参数构成这个表达式体表示为一个方法调用表达式）
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Expression<Func<double, double>> exp = a => Math.Sin(a);构建强类型的表达式树(表达式树字面量)
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UnaryExpression negate= Expression.Negate(left);//构建一元-表达式如：-a
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ConstantExpression strin= Expression.Constant("hello",typeof(string));
NewExpression negate = Expression.New(typeof(StringBuilder).GetConstructor(new Type[] { typeof(String) }), strin);
//构造new StringBuilder("hello")
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ParameterExpression a = Expression.Parameter(typeof(int), "a");
ParameterExpression b= Expression.Parameter(typeof(int), "b");
ParameterExpression i= Expression.Parameter(typeof(int), "i");
BinaryExpression add = Expression.Add(a,b);
ConstantExpression s=Expression.Constant(1);
BinaryExpression substract = Expression.Subtract(i,s);
NewArrayExpression arrayint= Expression.NewArrayInit(typeof(int), a, b, add);
IndexExpression arracc= Expression.ArrayAccess(arrayint, substract);
Console.WriteLine(arracc.ToString());
//new [] {a, b, (a + b)}[(i - 1)]数组访问
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MemberExpression mem=Expression.Property(exppro, property)//创建类型的属性表达式
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Expression.Equal(left, right)//二元=表达式
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Expression.GreaterThan(left, right)//二元>表达式
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Expression.GreaterThanOrEqual(left, right)//>=
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Expression.LessThan(left, right)//<
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Expression.LessThanOrEqual(left,right)/<=
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return Expression.Call(left, typeof (string).GetMethod("Contains"), right)//like 字符串中包含right表达式代表的字符串
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MethodCallExpression resultExp =
Expression.Call(
typeof (Enumerable),
"Contains",
new[] {left.Type},
right,
left)
//构造in 比如： c=>new[] {"nn","mm"}.contains(c.name)
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Expression.NotEqual(left, right)//!=
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Expression.Call(left, typeof (string).GetMethod("StartsWith", new[] {typeof (string)}), right)//left以right字符串开始
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Expression.Call(left, typeof (string).GetMethod("EndsWith", new[] {typeof (string)}), right)//left以right字符串结尾
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Expression.AndAlso(left, expression)//and 表达式&&
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Expression.OrElse(left, orGroupByExpAnd)//or表达式||
