LINQ Join Extensions

LINQ Join Extensions

using System;
using System.Collections.Generic;
using System.Linq;

namespace JoinExtensionExamples
{
    public static class JoinExtension
    {
        public static IEnumerable<TResult> LeftJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source,
                                                 IEnumerable<TInner> inner,
                                                 Func<TSource, TKey> primaryKey,
                                                 Func<TInner, TKey> foreignKey,
                                                 Func<TSource, TInner, TResult> resultCollection)
        {
            var result = from s in source
                         join i in inner
                             on primaryKey(s) equals foreignKey(i) into joinData
                         from left in joinData.DefaultIfEmpty()
                         select resultCollection(s, left);

            return result;
        }

        public static IEnumerable<TResult> RightJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source,
                                                  IEnumerable<TInner> inner,
                                                  Func<TSource, TKey> primaryKey,
                                                  Func<TInner, TKey> foreignKey,
                                                  Func<TSource, TInner, TResult> resultCollection)
        {
            var result = from i in inner
                         join s in source
                             on foreignKey(i) equals primaryKey(s) into joinData
                         from right in joinData.DefaultIfEmpty()
                         select resultCollection(right, i);

            return result;
        }

        public static IEnumerable<TResult> FullOuterJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source,
                                                          IEnumerable<TInner> inner,
                                                          Func<TSource, TKey> primaryKey,
                                                          Func<TInner, TKey> foreignKey,
                                                          Func<TSource, TInner, TResult> resultCollection)
        {
            IEnumerable<TSource> sourceCollection = source as IList<TSource> ?? source.ToList();
            IEnumerable<TInner> innerCollection = inner as IList<TInner> ?? inner.ToList();

            var left = sourceCollection.LeftJoin(innerCollection, primaryKey, foreignKey, resultCollection).ToList();
            var right = sourceCollection.RightJoin(innerCollection, primaryKey, foreignKey, resultCollection).ToList();

            return left.Union(right);
        }

        public static IEnumerable<TResult> LeftExclusiveJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source,
                                                          IEnumerable<TInner> inner,
                                                          Func<TSource, TKey> primaryKey,
                                                          Func<TInner, TKey> foreignKey,
                                                          Func<TSource, TInner, TResult> resultCollection)
        {
            var result = from s in source
                         join i in inner
                             on primaryKey(s) equals foreignKey(i) into joinData
                         from left in joinData.DefaultIfEmpty()
                         where left == null
                         select resultCollection(s, left);

            return result;
        }

        public static IEnumerable<TResult> RightExclusiveJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source,
                                                        IEnumerable<TInner> inner,
                                                        Func<TSource, TKey> primaryKey,
                                                        Func<TInner, TKey> foreignKey,
                                                        Func<TSource, TInner, TResult> resultCollection)
        {
            var result = from i in inner
                         join s in source
                             on foreignKey(i) equals primaryKey(s) into joinData
                         from right in joinData.DefaultIfEmpty()
                         where right == null
                         select resultCollection(right, i);

            return result;
        }

        public static IEnumerable<TResult> FullOuterExclusiveJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source,
                                                      IEnumerable<TInner> inner,
                                                      Func<TSource, TKey> primaryKey,
                                                      Func<TInner, TKey> foreignKey,
                                                      Func<TSource, TInner, TResult> resultCollection)
        {
            IEnumerable<TSource> sourceCollection = source as IList<TSource> ?? source.ToList();
            IEnumerable<TInner> innerCollection = inner as IList<TInner> ?? inner.ToList();

            var left = sourceCollection.LeftExclusiveJoin(innerCollection, primaryKey, foreignKey, resultCollection).ToList();
            var right = sourceCollection.RightExclusiveJoin(innerCollection, primaryKey, foreignKey, resultCollection).ToList();

            return left.Union(right);
        }
    }
}