80 lines
2.9 KiB
C#
80 lines
2.9 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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namespace APT.Infrastructure.Core
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{
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/// <summary>
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/// Expression表达式扩展操作类
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/// </summary>
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public static class ExpressionExtensions
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{
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/// <summary>
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/// 以特定的条件运行组合两个Expression表达式
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/// </summary>
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/// <typeparam name="T">表达式的主实体类型</typeparam>
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/// <param name="first">第一个Expression表达式</param>
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/// <param name="second">要组合的Expression表达式</param>
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/// <param name="merge">组合条件运算方式</param>
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/// <returns>组合后的表达式</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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Dictionary<ParameterExpression, ParameterExpression> map =
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first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
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Expression secondBody = ParameterRebinder.ReplaceParameters(map, 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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/// 以 Expression.AndAlso 组合两个Expression表达式
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/// </summary>
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/// <typeparam name="T">表达式的主实体类型</typeparam>
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/// <param name="first">第一个Expression表达式</param>
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/// <param name="second">要组合的Expression表达式</param>
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/// <returns>组合后的表达式</returns>
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public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
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{
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return first.Compose(second, Expression.AndAlso);
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}
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/// <summary>
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/// 以 Expression.OrElse 组合两个Expression表达式
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/// </summary>
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/// <typeparam name="T">表达式的主实体类型</typeparam>
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/// <param name="first">第一个Expression表达式</param>
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/// <param name="second">要组合的Expression表达式</param>
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/// <returns>组合后的表达式</returns>
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public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
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{
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return first.Compose(second, Expression.OrElse);
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}
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private class ParameterRebinder : ExpressionVisitor
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{
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private readonly Dictionary<ParameterExpression, ParameterExpression> _map;
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private ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
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{
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_map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
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}
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public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)
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{
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return new ParameterRebinder(map).Visit(exp);
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}
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protected override Expression VisitParameter(ParameterExpression node)
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{
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ParameterExpression replacement;
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if (_map.TryGetValue(node, out replacement))
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{
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node = replacement;
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}
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return base.VisitParameter(node);
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}
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}
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}
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} |