Saya pikir ada masalah dengan sebagian besar dari ini, termasuk jawaban yang diterima, karena mereka tidak bekerja dengan baik dengan Linq atas IQueryable baik karena melakukan bolak-balik server terlalu banyak dan terlalu banyak pengembalian data, atau melakukan terlalu banyak eksekusi klien.
Untuk IEnumerable, saya tidak suka jawaban Sehe atau serupa karena memiliki penggunaan memori yang berlebihan (tes daftar sederhana 10000000 menjalankan Linqpad kehabisan memori pada mesin 32GB saya).
Juga, sebagian besar yang lain tidak benar-benar menerapkan Full Outer Join yang tepat karena mereka menggunakan Union dengan Right Join daripada Concat dengan Right Anti Semi Join, yang tidak hanya menghilangkan duplikat inner join rows dari hasil, tetapi duplikat yang tepat yang ada awalnya di data kiri atau kanan.
Jadi di sini adalah ekstensi saya yang menangani semua masalah ini, menghasilkan SQL serta mengimplementasikan bergabung dalam LINQ ke SQL secara langsung, mengeksekusi di server, dan lebih cepat dan dengan memori lebih sedikit daripada yang lain di Enumerables:
public static class Ext {
public static IEnumerable<TResult> LeftOuterJoin<TLeft, TRight, TKey, TResult>(
this IEnumerable<TLeft> leftItems,
IEnumerable<TRight> rightItems,
Func<TLeft, TKey> leftKeySelector,
Func<TRight, TKey> rightKeySelector,
Func<TLeft, TRight, TResult> resultSelector) {
return from left in leftItems
join right in rightItems on leftKeySelector(left) equals rightKeySelector(right) into temp
from right in temp.DefaultIfEmpty()
select resultSelector(left, right);
}
public static IEnumerable<TResult> RightOuterJoin<TLeft, TRight, TKey, TResult>(
this IEnumerable<TLeft> leftItems,
IEnumerable<TRight> rightItems,
Func<TLeft, TKey> leftKeySelector,
Func<TRight, TKey> rightKeySelector,
Func<TLeft, TRight, TResult> resultSelector) {
return from right in rightItems
join left in leftItems on rightKeySelector(right) equals leftKeySelector(left) into temp
from left in temp.DefaultIfEmpty()
select resultSelector(left, right);
}
public static IEnumerable<TResult> FullOuterJoinDistinct<TLeft, TRight, TKey, TResult>(
this IEnumerable<TLeft> leftItems,
IEnumerable<TRight> rightItems,
Func<TLeft, TKey> leftKeySelector,
Func<TRight, TKey> rightKeySelector,
Func<TLeft, TRight, TResult> resultSelector) {
return leftItems.LeftOuterJoin(rightItems, leftKeySelector, rightKeySelector, resultSelector).Union(leftItems.RightOuterJoin(rightItems, leftKeySelector, rightKeySelector, resultSelector));
}
public static IEnumerable<TResult> RightAntiSemiJoin<TLeft, TRight, TKey, TResult>(
this IEnumerable<TLeft> leftItems,
IEnumerable<TRight> rightItems,
Func<TLeft, TKey> leftKeySelector,
Func<TRight, TKey> rightKeySelector,
Func<TLeft, TRight, TResult> resultSelector) {
var hashLK = new HashSet<TKey>(from l in leftItems select leftKeySelector(l));
return rightItems.Where(r => !hashLK.Contains(rightKeySelector(r))).Select(r => resultSelector(default(TLeft),r));
}
public static IEnumerable<TResult> FullOuterJoin<TLeft, TRight, TKey, TResult>(
this IEnumerable<TLeft> leftItems,
IEnumerable<TRight> rightItems,
Func<TLeft, TKey> leftKeySelector,
Func<TRight, TKey> rightKeySelector,
Func<TLeft, TRight, TResult> resultSelector) where TLeft : class {
return leftItems.LeftOuterJoin(rightItems, leftKeySelector, rightKeySelector, resultSelector).Concat(leftItems.RightAntiSemiJoin(rightItems, leftKeySelector, rightKeySelector, resultSelector));
}
private static Expression<Func<TP, TC, TResult>> CastSMBody<TP, TC, TResult>(LambdaExpression ex, TP unusedP, TC unusedC, TResult unusedRes) => (Expression<Func<TP, TC, TResult>>)ex;
public static IQueryable<TResult> LeftOuterJoin<TLeft, TRight, TKey, TResult>(
this IQueryable<TLeft> leftItems,
IQueryable<TRight> rightItems,
Expression<Func<TLeft, TKey>> leftKeySelector,
Expression<Func<TRight, TKey>> rightKeySelector,
Expression<Func<TLeft, TRight, TResult>> resultSelector) {
var sampleAnonLR = new { left = default(TLeft), rightg = default(IEnumerable<TRight>) };
var parmP = Expression.Parameter(sampleAnonLR.GetType(), "p");
var parmC = Expression.Parameter(typeof(TRight), "c");
var argLeft = Expression.PropertyOrField(parmP, "left");
var newleftrs = CastSMBody(Expression.Lambda(Expression.Invoke(resultSelector, argLeft, parmC), parmP, parmC), sampleAnonLR, default(TRight), default(TResult));
return leftItems.AsQueryable().GroupJoin(rightItems, leftKeySelector, rightKeySelector, (left, rightg) => new { left, rightg }).SelectMany(r => r.rightg.DefaultIfEmpty(), newleftrs);
}
public static IQueryable<TResult> RightOuterJoin<TLeft, TRight, TKey, TResult>(
this IQueryable<TLeft> leftItems,
IQueryable<TRight> rightItems,
Expression<Func<TLeft, TKey>> leftKeySelector,
Expression<Func<TRight, TKey>> rightKeySelector,
Expression<Func<TLeft, TRight, TResult>> resultSelector) {
var sampleAnonLR = new { leftg = default(IEnumerable<TLeft>), right = default(TRight) };
var parmP = Expression.Parameter(sampleAnonLR.GetType(), "p");
var parmC = Expression.Parameter(typeof(TLeft), "c");
var argRight = Expression.PropertyOrField(parmP, "right");
var newrightrs = CastSMBody(Expression.Lambda(Expression.Invoke(resultSelector, parmC, argRight), parmP, parmC), sampleAnonLR, default(TLeft), default(TResult));
return rightItems.GroupJoin(leftItems, rightKeySelector, leftKeySelector, (right, leftg) => new { leftg, right }).SelectMany(l => l.leftg.DefaultIfEmpty(), newrightrs);
}
public static IQueryable<TResult> FullOuterJoinDistinct<TLeft, TRight, TKey, TResult>(
this IQueryable<TLeft> leftItems,
IQueryable<TRight> rightItems,
Expression<Func<TLeft, TKey>> leftKeySelector,
Expression<Func<TRight, TKey>> rightKeySelector,
Expression<Func<TLeft, TRight, TResult>> resultSelector) {
return leftItems.LeftOuterJoin(rightItems, leftKeySelector, rightKeySelector, resultSelector).Union(leftItems.RightOuterJoin(rightItems, leftKeySelector, rightKeySelector, resultSelector));
}
private static Expression<Func<TP, TResult>> CastSBody<TP, TResult>(LambdaExpression ex, TP unusedP, TResult unusedRes) => (Expression<Func<TP, TResult>>)ex;
public static IQueryable<TResult> RightAntiSemiJoin<TLeft, TRight, TKey, TResult>(
this IQueryable<TLeft> leftItems,
IQueryable<TRight> rightItems,
Expression<Func<TLeft, TKey>> leftKeySelector,
Expression<Func<TRight, TKey>> rightKeySelector,
Expression<Func<TLeft, TRight, TResult>> resultSelector) {
var sampleAnonLgR = new { leftg = default(IEnumerable<TLeft>), right = default(TRight) };
var parmLgR = Expression.Parameter(sampleAnonLgR.GetType(), "lgr");
var argLeft = Expression.Constant(default(TLeft), typeof(TLeft));
var argRight = Expression.PropertyOrField(parmLgR, "right");
var newrightrs = CastSBody(Expression.Lambda(Expression.Invoke(resultSelector, argLeft, argRight), parmLgR), sampleAnonLgR, default(TResult));
return rightItems.GroupJoin(leftItems, rightKeySelector, leftKeySelector, (right, leftg) => new { leftg, right }).Where(lgr => !lgr.leftg.Any()).Select(newrightrs);
}
public static IQueryable<TResult> FullOuterJoin<TLeft, TRight, TKey, TResult>(
this IQueryable<TLeft> leftItems,
IQueryable<TRight> rightItems,
Expression<Func<TLeft, TKey>> leftKeySelector,
Expression<Func<TRight, TKey>> rightKeySelector,
Expression<Func<TLeft, TRight, TResult>> resultSelector) {
return leftItems.LeftOuterJoin(rightItems, leftKeySelector, rightKeySelector, resultSelector).Concat(leftItems.RightAntiSemiJoin(rightItems, leftKeySelector, rightKeySelector, resultSelector));
}
}
Perbedaan antara Right Anti-Semi-Join sebagian besar diperdebatkan dengan Linq to Objects atau di sumbernya, tetapi membuat perbedaan di sisi server (SQL) dalam jawaban akhir, menghapus yang tidak perlu JOIN .
Pengkodean tangan Expressionuntuk menangani penggabungan Expression<Func<>>ke dalam lambda dapat ditingkatkan dengan LinqKit, tetapi akan lebih baik jika bahasa / kompiler menambahkan bantuan untuk itu. Fungsi FullOuterJoinDistinctdan RightOuterJointermasuk untuk kelengkapan, tapi saya tidak menerapkan kembaliFullOuterGroupJoin .
Saya menulis versi lain untuk join luar penuhIEnumerable untuk kasus-kasus di mana kuncinya dapat dipesan, yaitu sekitar 50% lebih cepat daripada menggabungkan gabungan luar kiri dengan anti-bergabung kanan, setidaknya pada koleksi kecil. Ini melewati setiap koleksi setelah memilah hanya sekali.
Saya juga menambahkan jawaban lain untuk versi yang bekerja dengan EF dengan mengganti Invokedengan ekspansi kustom.