C# 好用的Expression动态拼接帮助类

public static class ExpressionHandle
{
    /// <summary>
    /// Linq的And操作
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="first"></param>
    /// <param name="second"></param>
    /// <param name="tf">是否拼接param>
    /// <returns>val为空就返回first，否则返回first与second的And操作</returns>
    public static Expression<Func<T, bool>> IfAnd<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second, bool tf)
    {
        if (tf)
        {
            return first.ExpressionAnd(second);
        }
        return first;
    }

    /// <summary>
    /// Linq的Or操作
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="first"></param>
    /// <param name="second"></param>
    /// <param name="tf">是否为拼接</param>
    /// <returns>val为空就返回first，否则返回first与second的Or操作</returns>
    public static Expression<Func<T, bool>> IfOr<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second, bool tf)
    {
        if (tf)
        {
            return first.ExpressionOr(second);
        }
        return first;
    }

    /// <summary>
    /// Linq的And操作
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="first"></param>
    /// <param name="second"></param>
    /// <param name="tf">是否拼接param>
    /// <returns>val为空就返回first，否则返回first与second的And操作</returns>
    public static Expression<Func<T1, T2, bool>> IfAnd<T1, T2>(this Expression<Func<T1, T2, bool>> first, Expression<Func<T1, T2, bool>> second, bool tf)
    {
        if (tf)
        {
            return first.ExpressionAnd(second);
        }
        return first;
    }

    /// <summary>
    /// Linq的Or操作
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="first"></param>
    /// <param name="second"></param>
    /// <param name="tf">是否为拼接</param>
    /// <returns>val为空就返回first，否则返回first与second的Or操作</returns>
    public static Expression<Func<T1, T2, bool>> IfOr<T1, T2>(this Expression<Func<T1, T2, bool>> first, Expression<Func<T1, T2, bool>> second, bool tf)
    {
        if (tf)
        {
            return first.ExpressionOr(second);
        }
        return first;
    }

    /// <summary>
    /// Linq的And操作
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="first"></param>
    /// <param name="second"></param>
    /// <param name="tf">是否拼接param>
    /// <returns>val为空就返回first，否则返回first与second的And操作</returns>
    public static Expression<Func<T1, T2, T3, bool>> IfAnd<T1, T2, T3>(this Expression<Func<T1, T2, T3, bool>> first, Expression<Func<T1, T2, T3, bool>> second, bool tf)
    {
        if (tf)
        {
            return first.ExpressionAnd(second);
        }
        return first;
    }

    /// <summary>
    /// Linq的Or操作
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="first"></param>
    /// <param name="second"></param>
    /// <param name="tf">是否为拼接</param>
    /// <returns>val为空就返回first，否则返回first与second的Or操作</returns>
    public static Expression<Func<T1, T2, T3, bool>> IfOr<T1, T2, T3>(this Expression<Func<T1, T2, T3, bool>> first, Expression<Func<T1, T2, T3, bool>> second, bool tf)
    {
        if (tf)
        {
            return first.ExpressionOr(second);
        }
        return first;
    }
}

public static class ExpressionHelper
{
    private static Expression<T> Combine<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
    {
        var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
        var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
        return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
    }
    /// <summary>
    /// And合并
    /// </summary>
    /// <returns></returns>
    public static Expression<Func<T, bool>> ExpressionAnd<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
    {
        return first.Combine(second, Expression.And);
    }
    /// <summary>
    /// OR合并
    /// </summary>
    /// <returns></returns>
    public static Expression<Func<T, bool>> ExpressionOr<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
    {
        return first.Combine(second, Expression.Or);
    }
    /// <summary>
    /// And合并
    /// </summary>
    /// <returns></returns>
    public static Expression<Func<T1, T2, bool>> ExpressionAnd<T1, T2>(this Expression<Func<T1, T2, bool>> first, Expression<Func<T1, T2, bool>> second)
    {
        return first.Combine(second, Expression.And);
    }
    /// <summary>
    /// OR合并
    /// </summary>
    /// <returns></returns>
    public static Expression<Func<T1, T2, bool>> ExpressionOr<T1, T2>(this Expression<Func<T1, T2, bool>> first, Expression<Func<T1, T2, bool>> second)
    {
        return first.Combine(second, Expression.Or);
    }
    /// <summary>
    /// And合并
    /// </summary>
    /// <returns></returns>
    public static Expression<Func<T1, T2, T3, bool>> ExpressionAnd<T1, T2, T3>(this Expression<Func<T1, T2, T3, bool>> first, Expression<Func<T1, T2, T3, bool>> second)
    {
        return first.Combine(second, Expression.And);
    }
    /// <summary>
    /// OR合并
    /// </summary>
    /// <returns></returns>
    public static Expression<Func<T1, T2, T3, bool>> ExpressionOr<T1, T2, T3>(this Expression<Func<T1, T2, T3, bool>> first, Expression<Func<T1, T2, T3, bool>> second)
    {
        return first.Combine(second, Expression.Or);
    }
}

public class ParameterRebinder : ExpressionVisitor
{
    private readonly Dictionary<ParameterExpression, ParameterExpression> map;
    /// <summary>
    /// 
    /// </summary>
    /// <param name="map"></param>
    public ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
    {
        this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
    }
    /// <summary>
    /// 
    /// </summary>
    /// <param name="map"></param>
    /// <param name="exp"></param>
    /// <returns></returns>
    public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)
    {
        return new ParameterRebinder(map).Visit(exp);
    }
    /// <summary>
    /// 
    /// </summary>
    /// <param name="p"></param>
    /// <returns></returns>
    protected override Expression VisitParameter(ParameterExpression p)
    {
        ParameterExpression replacement;
        if (map.TryGetValue(p, out replacement))
        {
            p = replacement;
        }
        return base.VisitParameter(p);
    }

}