c# Lambda扩展
2024-08-27 06:43:36
扩展类
public static class LinqExtensions
{
/// <summary>
/// 创建lambda表达式：p=>true
/// </summary>
/// <typeparam name="T">对象名称（类名）</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">对象名称（类名）</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">对象名称（类名）</typeparam>
/// <typeparam name="TKey">参数类型</typeparam>
/// <param name="propertyName">字段名称（数据库中字段名称）</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">对象名称（类名）</typeparam>
/// <param name="propertyName">字段名称（数据库中字段名称）</param>
/// <param name="propertyValue">数据值</param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateEqual<T>(string propertyName, object propertyValue, Type typeValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//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">对象名称（类名）</typeparam>
/// <param name="propertyName">字段名称（数据库中字段名称）</param>
/// <param name="propertyValue">数据值</param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateNotEqual<T>(string propertyName, object propertyValue, Type typeValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//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">对象名称（类名）</typeparam>
/// <param name="propertyName">字段名称（数据库中字段名称）</param>
/// <param name="propertyValue">数据值</param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateGreaterThan<T>(string propertyName, object propertyValue, Type typeValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//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小于propertyValue
/// </summary>
/// <typeparam name="T">对象名称（类名）</typeparam>
/// <param name="propertyName">字段名称（数据库中字段名称）</param>
/// <param name="propertyValue">数据值</param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateLessThan<T>(string propertyName, object propertyValue, Type typeValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//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">对象名称（类名）</typeparam>
/// <param name="propertyName">字段名称（数据库中字段名称）</param>
/// <param name="propertyValue">数据值</param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateGreaterThanOrEqual<T>(string propertyName, object propertyValue, Type typeValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//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 小于= propertyValue
/// </summary>
/// <typeparam name="T">对象名称（类名）</typeparam>
/// <param name="propertyName">字段名称（数据库中字段名称）</param>
/// <param name="propertyValue">数据值</param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateLessThanOrEqual<T>(string propertyName, object propertyValue, Type typeValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//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">对象名称（类名）</typeparam>
/// <param name="propertyName">字段名称（数据库中字段名称）</param>
/// <param name="propertyValue">数据值</param>
/// <returns></returns>
public 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">对象名称（类名）</typeparam>
/// <param name="propertyName">字段名称（数据库中字段名称）</param>
/// <param name="propertyValue">数据值</param>
/// <returns></returns>
public 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);
} /// <summary>
/// 功能描述:拼接Or
/// 作 者:beck.huang
/// 创建日期:2018-11-30 15:35:10
/// 任务编号:好餐谋后台管理系统
/// </summary>
/// <param name="expression1">expression1</param>
/// <param name="expression2">expression2</param>
/// <returns>返回值</returns>
public static Expression<Func<T, bool>> Or<T>(Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
{
return Compose(expression1, expression2, Expression.OrElse);
} /// <summary>
/// 功能描述:拼接And
/// 作 者:beck.huang
/// 创建日期:2018-11-30 15:35:18
/// 任务编号:好餐谋后台管理系统
/// </summary>
/// <param name="expression1">expression1</param>
/// <param name="expression2">expression2</param>
/// <returns>返回值</returns>
public static Expression<Func<T, bool>> And<T>(Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
{
return Compose(expression1, expression2, Expression.AndAlso);
} /// <summary>
/// 功能描述:合并2个表达式
/// 作 者:beck.huang
/// 创建日期:2018-11-30 15:35:26
/// 任务编号:好餐谋后台管理系统
/// </summary>
/// <param name="first">first</param>
/// <param name="second">second</param>
/// <param name="merge">merge</param>
/// <returns>返回值</returns>
public static Expression<T> Compose<T>(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);
}
private class ParameterRebinder : ExpressionVisitor
{
readonly Dictionary<ParameterExpression, ParameterExpression> map;
/// <summary>
/// Initializes a new instance of the <see cref="ParameterRebinder"/> class.
/// </summary>
/// <param name="map">The map.</param>
ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
{
this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
}
/// <summary>
/// Replaces the parameters.
/// </summary>
/// <param name="map">The map.</param>
/// <param name="exp">The exp.</param>
/// <returns>Expression</returns>
public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)
{
return new ParameterRebinder(map).Visit(exp);
}
protected override Expression VisitParameter(ParameterExpression p)
{
ParameterExpression replacement; if (map.TryGetValue(p, out replacement))
{
p = replacement;
}
return base.VisitParameter(p);
}
}
}
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