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Aucma.Scada/HighWayIot.Common/ExpressionExtensions.cs

150 lines
6.1 KiB
C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
namespace HighWayIot.Common
{
/// <summary>
/// 谓词表达式构建器
/// </summary>
public static class ExpressionExtensions
{
/// <summary>
/// 创建一个值恒为 <c>true</c> 的表达式。
/// </summary>
/// <typeparam name="T">表达式方法类型</typeparam>
/// <returns>一个值恒为 <c>true</c> 的表达式。</returns>
public static Expression<Func<T, bool>> True<T>() { return p => true; }
/// <summary>
/// 创建一个值恒为 <c>false</c> 的表达式。
/// </summary>
/// <typeparam name="T">表达式方法类型</typeparam>
/// <returns>一个值恒为 <c>false</c> 的表达式。</returns>
public static Expression<Func<T, bool>> False<T>() { return f => false; }
/// <summary>
/// 使用 Expression.OrElse 的方式拼接两个 System.Linq.Expression。
/// </summary>
/// <typeparam name="T">表达式方法类型</typeparam>
/// <param name="left">左边的 System.Linq.Expression 。</param>
/// <param name="right">右边的 System.Linq.Expression。</param>
/// <returns>拼接完成的 System.Linq.Expression。</returns>
public static Expression<T> Or<T>(this Expression<T> left, Expression<T> right)
{
return MakeBinary(left, right, Expression.OrElse);
}
/// <summary>
/// 使用 Expression.AndAlso 的方式拼接两个 System.Linq.Expression。
/// </summary>
/// <typeparam name="T">表达式方法类型</typeparam>
/// <param name="left">左边的 System.Linq.Expression 。</param>
/// <param name="right">右边的 System.Linq.Expression。</param>
/// <returns>拼接完成的 System.Linq.Expression。</returns>
public static Expression<T> And<T>(this Expression<T> left, Expression<T> right)
{
return MakeBinary(left, right, Expression.AndAlso);
}
/// <summary>
/// 使用自定义的方式拼接两个 System.Linq.Expression。
/// </summary>
/// <typeparam name="T">表达式方法类型</typeparam>
/// <param name="left">左边的 System.Linq.Expression 。</param>
/// <param name="right">右边的 System.Linq.Expression。</param>
/// <param name="func"> </param>
/// <returns>拼接完成的 System.Linq.Expression。</returns>
private static Expression<T> MakeBinary<T>(this Expression<T> left, Expression<T> right, Func<Expression, Expression, Expression> func)
{
return MakeBinary((LambdaExpression)left, right, func) as Expression<T>;
}
/// <summary>
/// 拼接两个 <paramref>
/// <name>System.Linq.Expression</name>
/// </paramref> ,两个 <paramref>
/// <name>System.Linq.Expression</name>
/// </paramref> 的参数必须完全相同。
/// </summary>
/// <param name="left">左边的 <paramref>
/// <name>System.Linq.Expression</name>
/// </paramref> </param>
/// <param name="right">右边的 <paramref>
/// <name>System.Linq.Expression</name>
/// </paramref> </param>
/// <param name="func">表达式拼接的具体逻辑</param>
/// <returns>拼接完成的 <paramref>
/// <name>System.Linq.Expression</name>
/// </paramref> </returns>
private static LambdaExpression MakeBinary(this LambdaExpression left, LambdaExpression right, Func<Expression, Expression, Expression> func)
{
var data = Combinate(right.Parameters, left.Parameters).ToArray();
right = ParameterReplace.Replace(right, data) as LambdaExpression;
return Expression.Lambda(func(left.Body, right.Body), left.Parameters.ToArray());
}
/// <summary>
/// 合并参数
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="left"></param>
/// <param name="right"></param>
/// <returns></returns>
private static IEnumerable<KeyValuePair<T, T>> Combinate<T>(IEnumerable<T> left, IEnumerable<T> right)
{
var a = left.GetEnumerator();
var b = right.GetEnumerator();
while (a.MoveNext() && b.MoveNext())
yield return new KeyValuePair<T, T>(a.Current, b.Current);
}
}
internal sealed class ParameterReplace : ExpressionVisitor
{
public static Expression Replace(Expression e, IEnumerable<KeyValuePair<ParameterExpression, ParameterExpression>> paramList)
{
var item = new ParameterReplace(paramList);
return item.Visit(e);
}
private readonly Dictionary<ParameterExpression, ParameterExpression> _parameters;
public ParameterReplace(IEnumerable<KeyValuePair<ParameterExpression, ParameterExpression>> paramList)
{
_parameters = paramList.ToDictionary(p => p.Key, p => p.Value, new ParameterEquality());
}
protected override Expression VisitParameter(ParameterExpression p)
{
ParameterExpression result;
if (_parameters.TryGetValue(p, out result))
return result;
return base.VisitParameter(p);
}
#region class: ParameterEquality
private class ParameterEquality : IEqualityComparer<ParameterExpression>
{
public bool Equals(ParameterExpression x, ParameterExpression y)
{
if (x == null || y == null)
return false;
return x.Type == y.Type;
}
public int GetHashCode(ParameterExpression obj)
{
if (obj == null)
return 0;
return obj.Type.GetHashCode();
}
}
#endregion
}
}