EF中扩展出Between操作符（修订版）

最新推荐文章于 2022-01-19 00:09:16 发布

愤怒的TryCatch

最新推荐文章于 2022-01-19 00:09:16 发布

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本文链接：https://blog.youkuaiyun.com/a406502972/article/details/83034470

本文介绍了一个Entity Framework (EF) 中用于实现Between操作的有效扩展方法。该方法允许开发者通过指定范围来筛选数据，例如按年龄范围筛选人员。通过使用表达式树来构建条件，此扩展方法确保了查询可以被EF正确解析并执行。

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随手记录一下，这是针对原文错误的修改。

原文：EF中扩展出Between操作符

直接使用是错误的，修改后的扩展方法：

/// <summary>
        /// 扩展 Between 操作符
        /// 使用 var query = db.People.Between(person => person.Age, 18, 21);
        /// </summary>
        /// <typeparam name="TSource"></typeparam>
        /// <typeparam name="TKey"></typeparam>
        /// <param name="source"></param>
        /// <param name="keySelector"></param>
        /// <param name="low"></param>
        /// <param name="high"></param>
        /// <returns></returns>
        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.Compile()).AsQueryable();
        }