59 lines
2.0 KiB
C#
59 lines
2.0 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Linq.Expressions;
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using System.Text;
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namespace Mini.Services
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{
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public static class PredicateExtensionses
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{
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public static Expression<Func<T, bool>> True<T>() { return f => true; }
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public static Expression<Func<T, bool>> False<T>() { return f => false; }
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public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expLeft, Expression<Func<T, bool>> expRight)
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{
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var candidateExpr = Expression.Parameter(typeof(T), "candidate");
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var parameterReplacer = new ParameterReplacer(candidateExpr);
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var left = parameterReplacer.Replace(expLeft.Body);
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var right = parameterReplacer.Replace(expRight.Body);
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var body = Expression.And(left, right);
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return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
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}
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public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expLeft, Expression<Func<T, bool>> expRight)
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{
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var candidateExpr = Expression.Parameter(typeof(T), "candidate");
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var parameterReplacer = new ParameterReplacer(candidateExpr);
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var left = parameterReplacer.Replace(expLeft.Body);
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var right = parameterReplacer.Replace(expRight.Body);
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var body = Expression.Or(left, right);
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return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
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}
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}
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internal class ParameterReplacer : ExpressionVisitor
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{
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public ParameterReplacer(ParameterExpression paramExpr)
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{
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this.ParameterExpression = paramExpr;
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}
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public ParameterExpression ParameterExpression { get; private set; }
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public Expression Replace(Expression expr)
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{
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return this.Visit(expr);
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}
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protected override Expression VisitParameter(ParameterExpression p)
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{
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return this.ParameterExpression;
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}
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}
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}
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