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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namespace YX.BLL
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{
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public static class PredicateBuilder
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{
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/// <summary>
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/// 机关函数应用True时:单个AND有效,多个AND有效;单个OR无效,多个OR无效;混应时写在AND后的OR有效
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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>() { return f => true; }
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/// <summary>
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/// 机关函数应用False时:单个AND无效,多个AND无效;单个OR有效,多个OR有效;混应时写在OR后面的AND有效
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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>() { return f => false; }
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public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
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{
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var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
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return Expression.Lambda<Func<T, bool>>(Expression.Or(expr1.Body, invokedExpr), expr1.Parameters);
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}
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public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
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{
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var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
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return Expression.Lambda<Func<T, bool>>(Expression.And(expr1.Body, invokedExpr), expr1.Parameters);
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}
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}
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}
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