Linq实现between拓展

先写一个拓展方法

static class Ext

{

   public static IQueryable<TSource> Between<TSource, TKey>

        (this IQueryable<TSource> source, 

         Expression<Func<TSource, TKey>> keySelector,

         TKey low, TKey high) where TKey : IComparable<TKey>

   {

       Expression key = Expression.Invoke(keySelector, 

            keySelector.Parameters.ToArray());

       Expression lowerBound = Expression.GreaterThanOrEqual

           (key, Expression.Constant(low));

       Expression upperBound = Expression.LessThanOrEqual

           (key, Expression.Constant(high));

       Expression and = Expression.AndAlso(lowerBound, upperBound);

       Expression<Func<TSource, bool>> lambda = 

           Expression.Lambda<Func<TSource, bool>>(and, keySelector.Parameters);

       return source.Where(lambda);

   }

}

调用

var query = db.People.Between(person => person.Age, 18, 21);