/***********************************************************************
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* Project: baifenBinfa
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* ProjectName: 百分兵法管理系统
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* Web: http://chuanyin.com
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* Author:
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* Email:
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* CreateTime: 202403/02
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* Description: 暂无
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***********************************************************************/
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using System;
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using System.Linq;
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using System.Linq.Expressions;
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namespace CoreCms.Net.Model.Entities.Expression
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{
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public static class PredicateBuilder
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{
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public static Expression<Func<T, bool>> True<T>()
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{
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return f => true;
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}
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public static Expression<Func<T, bool>> False<T>()
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{
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return f => false;
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}
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public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second,
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Func<System.Linq.Expressions.Expression, System.Linq.Expressions.Expression,
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System.Linq.Expressions.Expression> merge)
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{
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// build parameter map (from parameters of second to parameters of first)
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var map = first.Parameters.Select((f, i) => new {f, s = second.Parameters[i]})
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.ToDictionary(p => p.s, p => p.f);
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// replace parameters in the second lambda expression with parameters from the first
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var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
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// apply composition of lambda expression bodies to parameters from the first expression
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return System.Linq.Expressions.Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
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}
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/// <summary>
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/// 扩展啦
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/// </summary>
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/// <typeparam name="T"></typeparam>
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/// <param name="first"></param>
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/// <param name="second"></param>
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/// <returns></returns>
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public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first,
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Expression<Func<T, bool>> second)
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{
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return first.Compose(second, System.Linq.Expressions.Expression.AndAlso);
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}
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public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first,
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Expression<Func<T, bool>> second)
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{
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return first.Compose(second, System.Linq.Expressions.Expression.OrElse);
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}
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}
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}
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