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  • Entityframework lambda Join Extension

        public class DictionaryResult<TKey, TValue>
        {
            public TKey Key { get; set; }
            public IEnumerable<TValue> Values { get; set; }
        }
    
        public class JoinResult<TLeft, TRight>
        {
            public TLeft Left { get; set; }
            public TRight Right { get; set; }
        }
        public static class JoinExtension
        {
            /// <summary>
            /// 两表JOIN,以Key匹配,仅返回交集
            /// </summary>
            /// <typeparam name="T1"></typeparam>
            /// <typeparam name="T2"></typeparam>
            /// <typeparam name="TKey"></typeparam>
            /// <typeparam name="TResult"></typeparam>
            /// <param name="query"></param>
            /// <param name="another"></param>
            /// <param name="keySelector"></param>
            /// <param name="keySelector2"></param>
            /// <param name="resultSelector"></param>
            /// <returns></returns>
            public static IQueryable<TResult> InnerJoin<T1, T2, TKey, TResult>(this IQueryable<T1> query,
                IQueryable<T2> another,
                Expression<Func<T1, TKey>> keySelector,
                Expression<Func<T2, TKey>> keySelector2,
                Expression<Func<T1, T2, TResult>> resultSelector
                )
            {
                return query.Join(another, keySelector, keySelector2, resultSelector);
            }
    
            /// <summary>
            /// 两表JOIN,左表为主,以Key匹配右表数据。结果表示方式以左表行为Key,右表行为Values
            /// </summary>
            /// <typeparam name="T1"></typeparam>
            /// <typeparam name="T2"></typeparam>
            /// <typeparam name="TKey"></typeparam>
            /// <param name="query"></param>
            /// <param name="another"></param>
            /// <param name="keySelector"></param>
            /// <param name="keySelector2"></param>
            /// <returns></returns>
            public static IQueryable<DictionaryResult<T1, T2>> LeftJoinToDictionary<T1, T2, TKey>(this IQueryable<T1> query,
                IQueryable<T2> another,
                Expression<Func<T1, TKey>> keySelector,
                Expression<Func<T2, TKey>> keySelector2
                )
            {
                return query.GroupJoin(another, keySelector, keySelector2, (x, y) => new DictionaryResult<T1, T2> { Key = x, Values = y });
            }
    
            /// <summary>
            /// 两表JOIN,左表为主,以Key匹配右表数据。结果必有左表所有行,右表未有匹配行时其对应属性为NULL
            /// </summary>
            /// <typeparam name="T1"></typeparam>
            /// <typeparam name="T2"></typeparam>
            /// <typeparam name="TKey"></typeparam>
            /// <typeparam name="TResult"></typeparam>
            /// <param name="query"></param>
            /// <param name="another"></param>
            /// <param name="keySelector"></param>
            /// <param name="keySelector2"></param>
            /// <param name="resultSelector"></param>
            /// <returns></returns>
            public static IQueryable<TResult> LeftJoin<T1, T2, TKey, TResult>(this IQueryable<T1> query,
                IQueryable<T2> another,
                Expression<Func<T1, TKey>> keySelector,
                Expression<Func<T2, TKey>> keySelector2,
                Expression<Func<JoinResult<T1, T2>, TResult>> resultSelector
                )
            {
                return query.LeftJoinToDictionary(another, keySelector, keySelector2)
                    .SelectMany(x => x.Values.DefaultIfEmpty(), (x, y) => new JoinResult<T1, T2> { Left = x.Key, Right = y })
                    .Select(resultSelector);
            }
    
            /// <summary>
            /// 两表JOIN,右表为主,以Key匹配左表数据。结果表示方式以右表行为Key,左表行为Values
            /// </summary>
            /// <typeparam name="T1"></typeparam>
            /// <typeparam name="T2"></typeparam>
            /// <typeparam name="TKey"></typeparam>
            /// <param name="query"></param>
            /// <param name="another"></param>
            /// <param name="keySelector"></param>
            /// <param name="keySelector2"></param>
            /// <returns></returns>
            public static IQueryable<DictionaryResult<T2, T1>> RightJoinToDictionary<T1, T2, TKey>(this IQueryable<T1> query,
                IQueryable<T2> another,
                Expression<Func<T1, TKey>> keySelector,
                Expression<Func<T2, TKey>> keySelector2
                )
            {
                return another.GroupJoin(query, keySelector2, keySelector, (x, y) => new DictionaryResult<T2, T1> { Key = x, Values = y });
            }
    
    
            /// <summary>
            /// 两表JOIN,右表为主,以Key匹配左表数据。结果必有右表所有行,左表未有匹配行时其对应属性为NULL
            /// </summary>
            /// <typeparam name="T1"></typeparam>
            /// <typeparam name="T2"></typeparam>
            /// <typeparam name="TKey"></typeparam>
            /// <typeparam name="TResult"></typeparam>
            /// <param name="query"></param>
            /// <param name="another"></param>
            /// <param name="keySelector"></param>
            /// <param name="keySelector2"></param>
            /// <param name="resultSelector"></param>
            /// <returns></returns>
            public static IQueryable<TResult> RightJoin<T1, T2, TKey, TResult>(this IQueryable<T1> query,
                IQueryable<T2> another,
                Expression<Func<T1, TKey>> keySelector,
                Expression<Func<T2, TKey>> keySelector2,
                Expression<Func<JoinResult<T1, T2>, TResult>> resultSelector
                )
            {
                return another.RightJoinToDictionary(query, keySelector2, keySelector)
                    .SelectMany(x => x.Values.DefaultIfEmpty(), (x, y) => new JoinResult<T1, T2> { Left = x.Key, Right = y })
                    .Select(resultSelector);
            }
    }
    
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  • 原文地址:https://www.cnblogs.com/mrtiny/p/10395936.html
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