99 lines
3.6 KiB
C#
99 lines
3.6 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Linq.Expressions;
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using System.Text;
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using System.Threading.Tasks;
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namespace Yi.Framework.Infrastructure.Helper
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{
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public static class ExpressionHelper
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{
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/// <summary>
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/// Expression表达式树lambda参数拼接组合
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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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/// <param name="merge"></param>
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/// <returns></returns>
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public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
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{
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var parameterMap = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
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var secondBody = LambdaParameteRebinder.ReplaceParameter(parameterMap, second.Body);
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return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
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}
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/// <summary>
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/// Expression表达式树lambda参数拼接--false
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/// </summary>
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/// <typeparam name="T"></typeparam>
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/// <returns></returns>
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public static Expression<Func<T, bool>> False<T>() => f => false;
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/// <summary>
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/// Expression表达式树lambda参数拼接-true
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/// </summary>
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/// <typeparam name="T"></typeparam>
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/// <returns></returns>
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public static Expression<Func<T, bool>> True<T>() => f => true;
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/// <summary>
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/// Expression表达式树lambda参数拼接--and
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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, Expression<Func<T, bool>> second) => first.Compose(second, Expression.And);
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/// <summary>
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/// Expression表达式树lambda参数拼接--or
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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>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second) => first.Compose(second, Expression.Or);
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}
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public class LambdaParameteRebinder : ExpressionVisitor
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{
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/// <summary>
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/// 存放表达式树的参数的字典
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/// </summary>
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private readonly Dictionary<ParameterExpression, ParameterExpression> map;
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/// <summary>
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/// 构造函数
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/// </summary>
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/// <param name="map"></param>
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public LambdaParameteRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
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{
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this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
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}
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/// <summary>
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/// 重载参数访问的方法，访问表达式树参数，如果字典中包含，则取出
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/// </summary>
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/// <param name="node">表达式树参数</param>
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/// <returns></returns>
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protected override Expression VisitParameter(ParameterExpression node)
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{
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if (map.TryGetValue(node, out ParameterExpression expression))
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{
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node = expression;
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}
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return base.VisitParameter(node);
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}
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public static Expression ReplaceParameter(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)
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{
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return new LambdaParameteRebinder(map).Visit(exp);
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}
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}
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}
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