forked from ddrilling/AsbCloudServer
80 lines
2.9 KiB
C#
80 lines
2.9 KiB
C#
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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 AsbCloudInfrastructure
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{
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#nullable enable
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/// <summary>
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/// stolen from https://github.com/lotosbin/BinbinPredicateBuilder
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/// </summary>
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public static class PredicateBuilder
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{
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/// <summary>
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/// Combines the first predicate with the second using the logical "and".
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/// </summary>
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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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/// Combines the first predicate with the second using the logical "or".
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/// </summary>
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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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/// <summary>
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/// Negates the predicate.
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/// </summary>
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public static Expression<Func<T, bool>> Not<T>(this Expression<Func<T, bool>> expression)
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{
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var negated = Expression.Not(expression.Body);
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return Expression.Lambda<Func<T, bool>>(negated, expression.Parameters);
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}
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private 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 map = first.Parameters
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.Select((f, i) => new { f, s = second.Parameters[i] })
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.ToDictionary(p => p.s, p => p.f);
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var tryReplaceParametr = (Expression node) =>
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{
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if (node is ParameterExpression parameter)
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if (map.TryGetValue(parameter, out ParameterExpression? replacement))
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return replacement;
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return node;
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};
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var 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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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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this.map = map;
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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 parametr)
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{
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if (map.TryGetValue(parametr, out ParameterExpression? replacement))
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parametr = replacement;
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return parametr;
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}
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}
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}
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}
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#nullable disable
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