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);

}

}

}

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