使用Expression动态创建lambda表达式

using System;
using System.Linq.Expressions;
using System.Reflection;

namespace Helper
{
public class LambdaHelper
{
/// <summary>
/// 创建lambda表达式：p=>true
/// </summary>
/// <typeparam name="T"></typeparam>
/// <returns></returns>
public static Expression<Func<T, bool>> True<T>()
{
return p => true;
}

/// <summary>
/// 创建lambda表达式：p=>false
/// </summary>
/// <typeparam name="T"></typeparam>
/// <returns></returns>
public static Expression<Func<T, bool>> False<T>()
{
return p => false;
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName
/// </summary>
/// <typeparam name="T"></typeparam>
/// <typeparam name="TKey"></typeparam>
/// <param name="sort"></param>
/// <returns></returns>
public static Expression<Func<T, TKey>> GetOrderExpression<T, TKey>(string propertyName)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
return Expression.Lambda<Func<T, TKey>>(Expression.Property(parameter, propertyName), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName == propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateEqual<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.Equal(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName != propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="propertyName"></param>
/// <param name="propertyValue"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateNotEqual<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.NotEqual(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName > propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateGreaterThan<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.GreaterThan(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName < propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateLessThan<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.LessThan(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName >= propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateGreaterThanOrEqual<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.GreaterThanOrEqual(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName <= propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateLessThanOrEqual<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.LessThanOrEqual(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName.Contains(propertyValue)
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
private static Expression<Func<T, bool>> GetContains<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
ConstantExpression constant = Expression.Constant(propertyValue, typeof(string));
return Expression.Lambda<Func<T, bool>>(Expression.Call(member, method, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：!(p=>p.propertyName.Contains(propertyValue))
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
private static Expression<Func<T, bool>> GetNotContains<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
ConstantExpression constant = Expression.Constant(propertyValue, typeof(string));
return Expression.Lambda<Func<T, bool>>(Expression.Not(Expression.Call(member, method, constant)),parameter);
}
}
}

原文链接：https://blog.csdn.net/yl2isoft/article/details/53196092