107 lines
4.2 KiB
C#
107 lines
4.2 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 DG.Core
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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.OrElse(left, right);
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return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
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}
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/// <summary>
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/// And ((a or b )and (x or d))关系，但是and后面里面的关系是Or的关系，如 a.resid='' and ((a.channel>=1 and a.channel<10) or (a.channel>=50 and a.channel<60))
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/// </summary>
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/// <typeparam name="T"></typeparam>
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/// <param name="expLeft"></param>
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/// <param name="expRight"></param>
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/// <returns></returns>
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public static Expression<Func<T, bool>> AndListOr<T>(this Expression<Func<T, bool>> expLeft, Expression<Func<T, bool>>[] predicates)
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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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Expression<Func<T, bool>> lambda = predicates[0];
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for (int i = 1; i < predicates.Length; i++)
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{
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lambda = lambda.Or(predicates[i]);
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}
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var right = parameterReplacer.Replace(lambda.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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/// <summary>
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/// 传入条件之间为OR查询
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/// </summary>
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/// <typeparam name="T"></typeparam>
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/// <param name="source"></param>
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/// <param name="predicates"></param>
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/// <returns></returns>
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public static IQueryable<T> WhereOR<T>(this IQueryable<T> source, params Expression<Func<T, bool>>[] predicates)
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{
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if (source == null) throw new ArgumentNullException("source");
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if (predicates == null) throw new ArgumentNullException("predicates");
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if (predicates.Length == 0) return source.Where(x => true);
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if (predicates.Length == 1) return source.Where(predicates[0]);
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var param = Expression.Parameter(typeof(T), "x");
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Expression body = Expression.Invoke(predicates[0], param);
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for (int i = 1; i < predicates.Length; i++)
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{
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body = Expression.OrElse(body, Expression.Invoke(predicates[i], param));
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}
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var lambda = Expression.Lambda<Func<T, bool>>(body, param);
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return source.Where(lambda);
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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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