上一篇对Lambda表达式公共操作类进行了一些增强，本篇使用扩展方法对Lambda表达式进行扩展。
修改Util项目的Extensions.Expression.cs文件，代码如下。
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using Util.Lambdas;namespace Util {
/// <summary>
/// 表达式扩展
/// </summary>
public static partial class Extensions { #region Property(属性表达式) /// <summary>
/// 创建属性表达式
/// </summary>
/// <param name="expression">表达式</param>
/// <param name="propertyName">属性名,支持多级属性名，与句点分隔，范例：Customer.Name</param>
public static Expression Property( this Expression expression, string propertyName ) {
if ( propertyName.All( t => t != '.' ) )
return Expression.Property( expression, propertyName );
var propertyNameList = propertyName.Split( '.' );
Expression result = null;
for ( int i = ; i < propertyNameList.Length; i++ ) {
if ( i == ) {
result = Expression.Property( expression, propertyNameList[] );
continue;
}
result = result.Property( propertyNameList[i] );
}
return result;
} /// <summary>
/// 创建属性表达式
/// </summary>
/// <param name="expression">表达式</param>
/// <param name="member">属性</param>
public static Expression Property( this Expression expression, MemberInfo member ) {
return Expression.MakeMemberAccess( expression, member );
} #endregion #region Operation(操作) /// <summary>
/// 操作
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="operator">运算符</param>
/// <param name="value">值</param>
public static Expression Operation( this Expression left, Operator @operator, object value ) {
switch ( @operator ) {
case Operator.Equal:
return left.Equal( value );
case Operator.NotEqual:
return left.NotEqual( value );
case Operator.Greater:
return left.Greater( value );
case Operator.Less:
return left.Less( value );
case Operator.GreaterEqual:
return left.GreaterEqual( value );
case Operator.LessEqual:
return left.LessEqual( value );
case Operator.Contains:
return left.Call( "Contains", value );
case Operator.Starts:
return left.StartsWith( value );
case Operator.Ends:
return left.EndsWith( value );
}
throw new NotImplementedException();
} #endregion #region StartsWith(头匹配) /// <summary>
/// 头匹配
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="value">值</param>
public static Expression StartsWith( this Expression left, object value ) {
return left.Call( "StartsWith", new[] { typeof( string ) }, value );
} #endregion #region EndsWith(尾匹配) /// <summary>
/// 尾匹配
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="value">值</param>
public static Expression EndsWith( this Expression left, object value ) {
return left.Call( "EndsWith", new[] { typeof( string ) }, value );
} #endregion #region Call(调用方法表达式) /// <summary>
/// 创建调用方法表达式
/// </summary>
/// <param name="instance">调用的实例</param>
/// <param name="methodName">方法名</param>
/// <param name="values">参数值列表</param>
public static Expression Call( this Expression instance, string methodName, params Expression[] values ) {
return Expression.Call( instance, instance.Type.GetMethod( methodName ), values );
} /// <summary>
/// 创建调用方法表达式
/// </summary>
/// <param name="instance">调用的实例</param>
/// <param name="methodName">方法名</param>
/// <param name="values">参数值列表</param>
public static Expression Call( this Expression instance, string methodName, params object[] values ) {
if ( values == null || values.Length == )
return Expression.Call( instance, instance.Type.GetMethod( methodName ) );
return Expression.Call( instance, instance.Type.GetMethod( methodName ), values.Select( Expression.Constant ) );
} /// <summary>
/// 创建调用方法表达式
/// </summary>
/// <param name="instance">调用的实例</param>
/// <param name="methodName">方法名</param>
/// <param name="paramTypes">参数类型列表</param>
/// <param name="values">参数值列表</param>
public static Expression Call( this Expression instance, string methodName, Type[] paramTypes, params object[] values ) {
if ( values == null || values.Length == )
return Expression.Call( instance, instance.Type.GetMethod( methodName, paramTypes ) );
return Expression.Call( instance, instance.Type.GetMethod( methodName, paramTypes ), values.Select( Expression.Constant ) );
} #endregion #region Equal(等于表达式) /// <summary>
/// 创建等于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="right">右操作数</param>
public static Expression Equal( this Expression left, Expression right ) {
return Expression.Equal( left, right );
} /// <summary>
/// 创建等于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="value">值</param>
public static Expression Equal( this Expression left, object value ) {
return left.Equal( Lambda.Constant( left, value ) );
} #endregion #region NotEqual(不等于表达式) /// <summary>
/// 创建不等于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="right">右操作数</param>
public static Expression NotEqual( this Expression left, Expression right ) {
return Expression.NotEqual( left, right );
} /// <summary>
/// 创建不等于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="value">值</param>
public static Expression NotEqual( this Expression left, object value ) {
return left.NotEqual( Lambda.Constant( left, value ) );
} #endregion #region Greater(大于表达式) /// <summary>
/// 创建大于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="right">右操作数</param>
public static Expression Greater( this Expression left, Expression right ) {
return Expression.GreaterThan( left, right );
} /// <summary>
/// 创建大于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="value">值</param>
public static Expression Greater( this Expression left, object value ) {
return left.Greater( Lambda.Constant( left, value ) );
} #endregion #region Less(小于表达式) /// <summary>
/// 创建小于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="right">右操作数</param>
public static Expression Less( this Expression left, Expression right ) {
return Expression.LessThan( left, right );
} /// <summary>
/// 创建小于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="value">值</param>
public static Expression Less( this Expression left, object value ) {
return left.Less( Lambda.Constant( left, value ) );
} #endregion #region GreaterEqual(大于等于表达式) /// <summary>
/// 创建大于等于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="right">右操作数</param>
public static Expression GreaterEqual( this Expression left, Expression right ) {
return Expression.GreaterThanOrEqual( left, right );
} /// <summary>
/// 创建大于等于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="value">值</param>
public static Expression GreaterEqual( this Expression left, object value ) {
return left.GreaterEqual( Lambda.Constant( left, value ) );
} #endregion #region LessEqual(小于等于表达式) /// <summary>
/// 创建小于等于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="right">右操作数</param>
public static Expression LessEqual( this Expression left, Expression right ) {
return Expression.LessThanOrEqual( left, right );
} /// <summary>
/// 创建小于等于运算表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="value">值</param>
public static Expression LessEqual( this Expression left, object value ) {
return left.LessEqual( Lambda.Constant( left, value ) );
} #endregion #region Compose(组合表达式) /// <summary>
/// 组合表达式
/// </summary>
/// <typeparam name="T">对象类型</typeparam>
/// <param name="first">左操作数</param>
/// <param name="second">右操作数</param>
/// <param name="merge">合并操作</param>
internal static Expression<T> Compose<T>( this Expression<T> first, Expression<T> second,
Func<Expression, Expression, Expression> merge ) {
var map = first.Parameters.Select( ( f, i ) => new { f, s = second.Parameters[i] } ).ToDictionary( p => p.s, p => p.f );
var secondBody = ParameterRebinder.ReplaceParameters( map, second.Body );
return Expression.Lambda<T>( merge( first.Body, secondBody ), first.Parameters );
} #endregion #region And(与表达式) /// <summary>
/// 与操作表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="right">右操作数</param>
public static Expression And( this Expression left, Expression right ) {
if ( left == null )
return right;
if ( right == null )
return left;
return Expression.AndAlso( left, right );
} /// <summary>
/// 与操作表达式
/// </summary>
/// <typeparam name="T">对象类型</typeparam>
/// <param name="left">左操作数</param>
/// <param name="right">右操作数</param>
public static Expression<Func<T, bool>> And<T>( this Expression<Func<T, bool>> left, Expression<Func<T, bool>> right ) {
if ( left == null )
return right;
if ( right == null )
return left;
return left.Compose( right, Expression.AndAlso );
} #endregion #region Or(或表达式) /// <summary>
/// 或操作表达式
/// </summary>
/// <param name="left">左操作数</param>
/// <param name="right">右操作数</param>
public static Expression Or( this Expression left, Expression right ) {
return Expression.OrElse( left, right );
} /// <summary>
/// 或操作表达式
/// </summary>
/// <typeparam name="T">对象类型</typeparam>
/// <param name="first">左操作数</param>
/// <param name="second">右操作数</param>
/// <returns></returns>
public static Expression<Func<T, bool>> Or<T>( this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second ) {
return first.Compose( second, Expression.OrElse );
} #endregion #region Value(获取lambda表达式的值) /// <summary>
/// 获取lambda表达式的值
/// </summary>
/// <typeparam name="T">对象类型</typeparam>
public static object Value<T>( this Expression<Func<T, bool>> expression ) {
return Lambda.GetValue( expression );
} #endregion #region ToLambda(创建Lambda表达式) /// <summary>
/// 创建Lambda表达式
/// </summary>
/// <typeparam name="TDelegate">委托类型</typeparam>
/// <param name="body">表达式</param>
/// <param name="parameters">参数列表</param>
public static Expression<TDelegate> ToLambda<TDelegate>( this Expression body, params ParameterExpression[] parameters ) {
return Expression.Lambda<TDelegate>( body, parameters );
} #endregion
}
}
在Util项目中添加Operator枚举，代码如下。
using System.ComponentModel;namespace Util {
/// <summary>
/// 操作符
/// </summary>
public enum Operator {
/// <summary>
/// 等于
/// </summary>
[Description( "等于" )]
Equal,
/// <summary>
/// 不等于
/// </summary>
[Description( "不等于" )]
NotEqual,
/// <summary>
/// 大于
/// </summary>
[Description( "大于" )]
Greater,
/// <summary>
/// 小于
/// </summary>
[Description( "小于" )]
Less,
/// <summary>
/// 大于等于
/// </summary>
[Description( "大于等于" )]
GreaterEqual,
/// <summary>
/// 小于等于
/// </summary>
[Description( "小于等于" )]
LessEqual,
/// <summary>
/// 头尾匹配
/// </summary>
[Description( "头尾匹配" )]
Contains,
/// <summary>
/// 头匹配
/// </summary>
[Description( "头匹配" )]
Starts,
/// <summary>
/// 尾匹配
/// </summary>
[Description( "尾匹配" )]
Ends
}
}
找到Util.Tests测试项目，修改Extensions目录下的ExpressionExtensionTest，代码如下。
using System;
using System.Linq.Expressions;
using Microsoft.VisualStudio.TestTools.UnitTesting;namespace Util.Tests.Extensions {
/// <summary>
/// 表达式扩展测试
/// </summary>
[TestClass]
public class ExpressionExtensionTest { #region 测试初始化 /// <summary>
/// 参数表达式
/// </summary>
private ParameterExpression _parameterExpression; /// <summary>
/// 表达式1
/// </summary>
private Expression _expression1; /// <summary>
/// 表达式2
/// </summary>
private Expression _expression2; /// <summary>
/// 测试初始化
/// </summary>
[TestInitialize]
public void TestInit() {
_parameterExpression = Expression.Parameter( typeof( Person ), "t" );
_expression1 = _parameterExpression.Property( "Name" ).Call( "Contains", Expression.Constant( "A" ) );
_expression2 = _parameterExpression.Property( "Birthday" )
.Property( "Value" )
.Property( "Year" )
.Greater( Expression.Constant( ) );
} #endregion #region And(与操作) /// <summary>
/// 测试And方法，连接两个表达式
/// </summary>
[TestMethod]
public void TestAnd() {
var andExpression = _expression1.And( _expression2 ).ToLambda<Func<Person, bool>>( _parameterExpression );
Expression<Func<Person, bool>> expected = t => t.Name.Contains( "A" ) && t.Birthday.Value.Year > ;
Assert.AreEqual( expected.ToString(), andExpression.ToString() );
} /// <summary>
/// 测试And方法，连接两个表达式
/// </summary>
[TestMethod]
public void TestAnd_2() {
Expression<Func<Person, bool>> left = t => t.Name == "A";
Expression<Func<Person, bool>> right = t => t.Name == "B";
Expression<Func<Person, bool>> expected = t => t.Name == "A" && t.Name == "B";
Assert.AreEqual( expected.ToString(), left.And( right ).ToString() );
} #endregion #region Or(或操作) /// <summary>
/// 测试Or方法，连接两个表达式
/// </summary>
[TestMethod]
public void TestOr() {
var andExpression = _expression1.Or( _expression2 ).ToLambda<Func<Person, bool>>( _parameterExpression );
Expression<Func<Person, bool>> expected = t => t.Name.Contains( "A" ) || t.Birthday.Value.Year > ;
Assert.AreEqual( expected.ToString(), andExpression.ToString() );
} /// <summary>
/// 测试Or方法，连接两个表达式
/// </summary>
[TestMethod]
public void TestOr_2() {
Expression<Func<Person, bool>> left = t => t.Name == "A";
Expression<Func<Person, bool>> right = t => t.Name == "B";
Expression<Func<Person, bool>> expected = t => t.Name == "A" || t.Name == "B";
Assert.AreEqual( expected.ToString(), left.Or( right ).ToString() );
} #endregion #region Value(获取成员值) /// <summary>
/// 获取成员值
/// </summary>
[TestMethod]
public void TestValue() {
Expression<Func<Person, bool>> expression = test => test.Name == "A";
Assert.AreEqual( "A", expression.Value() );
} #endregion #region 运算符操作 /// <summary>
/// 测试相等
/// </summary>
[TestMethod]
public void TestEqual_Nullable() {
_expression1 = _parameterExpression.Property( "Age" ).Equal( );
Assert.AreEqual( "t => (t.Age == 1)",
_expression1.ToLambda<Func<Person, bool>>( _parameterExpression ).ToString() );
} /// <summary>
/// 测试不相等
/// </summary>
[TestMethod]
public void TestNotEqual_Nullable() {
_expression1 = _parameterExpression.Property( "Age" ).NotEqual( );
Assert.AreEqual( "t => (t.Age != 1)",
_expression1.ToLambda<Func<Person, bool>>( _parameterExpression ).ToString() );
} /// <summary>
/// 测试大于
/// </summary>
[TestMethod]
public void TestGreater_Nullable() {
_expression1 = _parameterExpression.Property( "Age" ).Greater( );
Assert.AreEqual( "t => (t.Age > 1)",
_expression1.ToLambda<Func<Person, bool>>( _parameterExpression ).ToString() );
} /// <summary>
/// 测试大于等于
/// </summary>
[TestMethod]
public void TestGreaterEqual_Nullable() {
_expression1 = _parameterExpression.Property( "Age" ).GreaterEqual( );
Assert.AreEqual( "t => (t.Age >= 1)",
_expression1.ToLambda<Func<Person, bool>>( _parameterExpression ).ToString() );
} /// <summary>
/// 测试小于
/// </summary>
[TestMethod]
public void TestLess_Nullable() {
_expression1 = _parameterExpression.Property( "Age" ).Less( );
Assert.AreEqual( "t => (t.Age < 1)",
_expression1.ToLambda<Func<Person, bool>>( _parameterExpression ).ToString() );
} /// <summary>
/// 测试小于等于
/// </summary>
[TestMethod]
public void TestLessEqual_Nullable() {
_expression1 = _parameterExpression.Property( "Age" ).LessEqual( );
Assert.AreEqual( "t => (t.Age <= 1)",
_expression1.ToLambda<Func<Person, bool>>( _parameterExpression ).ToString() );
} #endregion #region Person（测试类） /// <summary>
/// 测试
/// </summary>
public class Person {
public string Name { get; set; }
public int? Age { get; set; }
public DateTime? Birthday { get; set; }
} #endregion
}
}
需要注意的是，如果需要合并表达式，比如And或Or操作，需要用到一个ParameterRebinder类，它从ExpressionVisitor派生，这个类我是从国外一个网站上直接Copy过来的，代码如下。
using System.Collections.Generic;
using System.Linq.Expressions;namespace Util.Lambdas {
/// <summary>
/// 参数重绑定操作
/// </summary>
public class ParameterRebinder : ExpressionVisitor {
/// <summary>
/// 参数字典
/// </summary>
private readonly Dictionary<ParameterExpression, ParameterExpression> _map; /// <summary>
/// 初始化参数重绑定操作
/// </summary>
/// <param name="map">参数字典</param>
public ParameterRebinder( Dictionary<ParameterExpression, ParameterExpression> map ) {
_map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
} /// <summary>
/// 替换参数
/// </summary>
/// <param name="map">参数字典</param>
/// <param name="exp">表达式</param>
public static Expression ReplaceParameters( Dictionary<ParameterExpression, ParameterExpression> map, Expression exp ) {
return new ParameterRebinder( map ).Visit( exp );
} /// <summary>
/// 访问参数
/// </summary>
/// <param name="parameterExpression">参数</param>
protected override Expression VisitParameter( ParameterExpression parameterExpression ) {
ParameterExpression replacement;
if ( _map.TryGetValue( parameterExpression, out replacement ) )
parameterExpression = replacement;
return base.VisitParameter( parameterExpression );
}
}
}
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