Data structures 如何在Neo4J中处理队列？

在我的Neo4J数据库中，我有一系列通过双链表实现的卡片队列。数据结构如下图所示（使用Alistair Jones的在线工具生成的队列SVG图）：

因为这些是队列，所以我总是从队列的尾部添加新项目。我知道双重关系（next/previous）是不必要的，但它们简化了双向遍历，所以我更喜欢使用它们

插入新节点 这是我用来插入新“卡”的查询：

查询可以分为两部分。第一部分：

MATCH (currentList:List)-[currentTailRel:TailCard]->(currentTail:Card) WHERE ID(currentList) = {{LIST_ID}}
CREATE (currentList)-[newTailRel:TailCard]->(newCard:Card { title: {{TITLE}}, description: {{DESCRIPTION}} })
CREATE (newCard)-[newPrevRel:PreviousCard]->(currentTail)
CREATE (currentTail)-[newNextRel:NextCard]->(newCard)
DELETE currentTailRel

我处理将一张卡添加到已经有其他卡的队列的一般情况。 第二部分：

WITH count(newCard) as countNewCard
WHERE countNewCard = 0
MATCH (emptyList:List)-[fakeTailRel:TailCard]->(emptyList), 
(emptyList)-[fakeHeadRel:HeadCard]->(emptyList) 
WHERE ID(emptyList) = {{LIST_ID}}
WITH emptyList, fakeTailRel, fakeHeadRel
CREATE (emptyList)-[:TailCard]->(newCard:Card { title: {{TITLE}}, description: {{DESCRIPTION}} })
CREATE (emptyList)-[:HeadCard]->(newCard)
DELETE fakeTailRel, fakeHeadRel
RETURN true

我处理队列中没有卡的情况。在这种情况下，（emptyList）节点有两种类型的关系HeadCard和TailCard指向自身（我称它们为fake tail和fake head）

这似乎奏效了。不过，作为一个不速之客，我有一种感觉，就是我想得太多了，可能有一种更优雅、更直接的方式来实现这一点。例如，我想了解如何更好/更简单地处理这两个子查询。如果可能的话，我还希望能够在这两种情况下返回新创建的节点

存档现有节点 下面是我如何从队列中删除节点。我不想简单地删除节点，我宁愿将它们添加到存档节点，以便在需要时可以恢复它们。 我已查明这些案件：

当要存档的节点位于队列的中间时

// archive a node in the middle of a doubly-linked list
MATCH (before:Card)-[n1:NextCard]->(middle:Card)-[n2:NextCard]->(after:Card) 
WHERE ID(middle)=48
CREATE (before)-[:NextCard]->(after)
CREATE (after)-[:PreviousCard]->(before)
WITH middle, before, after
MATCH (middle)-[r]-(n)
DELETE r
WITH middle, before, after
MATCH (before)<-[:NextCard*]-(c:Card)<-[:HeadCard]-(l:List)<-[:NextList*]-(fl:List)<-[:HeadList]-(p:Project)-[:ArchiveList]->(archive:List)
CREATE (archive)-[r:Archived { archivedOn : timestamp() }]->(middle)
RETURN middle

// archive the head node of a doubly-linked list
MATCH (list:List)-[h1:HeadCard]->(head:Card)-[n1:NextCard]->(second:Card) 
WHERE ID(head)=48
CREATE (list)-[:HeadCard]->(second)
WITH head, list
MATCH (head)-[r]-(n)
DELETE r
WITH head, list
MATCH (list)<-[:NextList*]-(fl:List)<-[:HeadList]-(p:Project)-[:ArchiveList]->(archive:List)
CREATE (archive)-[r:Archived { archivedOn : timestamp() }]->(head)
RETURN head

// archive the tail node of a doubly-linked list
MATCH (list:List)-[t1:TailCard]->(tail:Card)-[p1:PreviousCard]->(nextToLast:Card) 
WHERE ID(tail)=48
CREATE (list)-[:TailCard]->(nextToLast)
WITH tail, list
MATCH (tail)-[r]-(n)
DELETE r
WITH tail, list
MATCH (list)<-[:NextList*]-(fl:List)<-[:HeadList]-(p:Project)-[:ArchiveList]->(archive:List)
CREATE (archive)-[r:Archived { archivedOn : timestamp() }]->(tail)
RETURN tail

// archive the one and only node in the doubly-linked list
MATCH (list:List)-[tc:TailCard]->(only:Card)<-[hc:HeadCard]-(list:List) 
WHERE ID(only)=48
CREATE (list)-[:TailCard]->(list)
CREATE (list)-[:HeadCard]->(list)
WITH only, list
MATCH (only)-[r]-(n)
DELETE r
WITH only, list
MATCH (list)<-[:NextList*]-(fl:List)<-[:HeadList]-(p:Project)-[:ArchiveList]->(archive:List)
CREATE (archive)-[r:Archived { archivedOn : timestamp() }]->(only)
RETURN only

我还是会陷入一个无限循环或者其他什么。。。 因此，我猜before为NULL时的行

大小写然后[]ELSE COLLECT（before）END AS beforeList

不是一个好主意。。。关于如何从这里开始有什么建议吗？我走错路了吗

---

解决方案？ 最后，经过大量研究，我找到了一种编写单个查询的方法，该查询可以处理所有可能的场景。我不知道这是否是实现我想要实现的目标的最佳方式，但对我来说，它似乎足够优雅和紧凑。你觉得怎么样

// first let's get a hold of the card we want to archive
MATCH (theCard:Card) WHERE ID(theCard)=44
// next, let's get a hold of the correspondent archive list node, since we need to move the card in that list
OPTIONAL MATCH (theCard)<-[:NEXT_CARD|HEAD_CARD*]-(theList:List)<-[:NEXT_LIST|HEAD_LIST*]-(theProject:Project)-[:ARCHIVE_LIST]->(theArchive:List)
// let's check if we are in the case where the card to be archived is in the middle of a list
OPTIONAL MATCH (before:Card)-[btc:NEXT_CARD]->(theCard:Card)-[tca:NEXT_CARD]->(after:Card) 
OPTIONAL MATCH (next:Card)-[ntc:PREV_CARD]->(theCard:Card)-[tcp:PREV_CARD]->(previous:Card) 
// let's check if the card to be archived is the only card in the list
OPTIONAL MATCH (listOfOne:List)-[lootc:TAIL_CARD]->(theCard:Card)<-[tcloo:HEAD_CARD]-(listOfOne:List)
// let's check if the card to be archived is at the head of the list
OPTIONAL MATCH (listToHead:List)-[lthtc:HEAD_CARD]->(theCard:Card)-[tcs:NEXT_CARD]->(second:Card)-[stc:PREV_CARD]->(theCard:Card) 
// let's check if the card to be archived is at the tail of the list
OPTIONAL MATCH (listToTail:List)-[ltttc:TAIL_CARD]->(theCard:Card)-[tcntl:PREV_CARD]->(nextToLast:Card)-[ntltc:NEXT_CARD]->(theCard:Card) 
WITH 
    theCard, theList, theProject, theArchive,
    CASE WHEN theArchive IS NULL THEN [] ELSE [(theArchive)] END AS archives,
    CASE WHEN before IS NULL THEN [] ELSE [(before)] END AS befores, 
    before, btc, tca, after, 
    CASE WHEN next IS NULL THEN [] ELSE [(next)] END AS nexts, 
    next, ntc, tcp, previous, 
    CASE WHEN listOfOne IS NULL THEN [] ELSE [(listOfOne)] END AS listsOfOne, 
    listOfOne, lootc, tcloo, 
    CASE WHEN listToHead IS NULL THEN [] ELSE [(listToHead)] END AS listsToHead, 
    listToHead, lthtc, tcs, second, stc, 
    CASE WHEN listToTail IS NULL THEN [] ELSE [(listToTail)] END AS listsToTail, 
    listToTail, ltttc, tcntl, nextToLast, ntltc
// let's handle the case in which the archived card was in the middle of a list
FOREACH (value IN befores | 
    CREATE (before)-[:NEXT_CARD]->(after)
    CREATE (after)-[:PREV_CARD]->(before)
    DELETE btc, tca)
FOREACH (value IN nexts | DELETE ntc, tcp)
// let's handle the case in which the archived card was the one and only card in the list
FOREACH (value IN listsOfOne | 
    CREATE (listOfOne)-[:HEAD_CARD]->(listOfOne)
    CREATE (listOfOne)-[:TAIL_CARD]->(listOfOne)
    DELETE lootc, tcloo)
// let's handle the case in which the archived card was at the head of the list
FOREACH (value IN listsToHead | 
    CREATE (listToHead)-[:HEAD_CARD]->(second)
    DELETE lthtc, tcs, stc)
// let's handle the case in which the archived card was at the tail of the list
FOREACH (value IN listsToTail | 
    CREATE (listToTail)-[:TAIL_CARD]->(nextToLast)
    DELETE ltttc, tcntl, ntltc)
// finally, let's move the card in the archive  
// first get a hold of the archive list to which we want to add the card
WITH 
    theCard, 
    theArchive
// first get a hold of the list to which we want to add the new card
OPTIONAL MATCH (theArchive)-[tact:TAIL_CARD]->(currentTail:Card)
// check if the list is empty
OPTIONAL MATCH (theArchive)-[tata1:TAIL_CARD]->(theArchive)-[tata2:HEAD_CARD]->(theArchive)
WITH
    theArchive, theCard,
    CASE WHEN currentTail IS NULL THEN [] ELSE [(currentTail)] END AS currentTails,
    currentTail, tact,
    CASE WHEN tata1 IS NULL THEN [] ELSE [(theArchive)] END AS emptyLists,
    tata1, tata2
// handle the case in which the list already had at least one card
FOREACH (value IN currentTails | 
    CREATE (theArchive)-[:TAIL_CARD]->(theCard)
    CREATE (theCard)-[:PREV_CARD]->(currentTail)
    CREATE (currentTail)-[:NEXT_CARD]->(theCard)
    DELETE tact)
// handle the case in which the list was empty
FOREACH (value IN emptyLists |
    CREATE (theArchive)-[:TAIL_CARD]->(theCard)
    CREATE (theArchive)-[:HEAD_CARD]->(theCard)
    DELETE tata1, tata2)
RETURN theCard

存档卡片 现在让我们重新考虑一下我们想要归档卡片的用例。让我们回顾一下体系结构：

我们有：

• 每个项目都有一个列表队列
• 每个项目都有一个存档队列来存储所有存档卡
• 每个列表都有一个卡片队列

在前面的队列体系结构中，我有4种不同的场景，这取决于要归档的卡是头部、尾部还是中间的一张卡，或者它是否是队列中剩下的最后一张卡

现在，随着头节点和尾节点的引入，只有一种情况，因为头节点和尾节点在那里停留，即使在队列为空的情况下：

• 我们需要找到（上一个）和（下一个）节点，在（card）节点之前和之后，这是我们要归档的节点
• 然后，我们需要用[next_CARD]和[PREV_CARD]关系连接（previous）和（next）
• 然后，我们需要删除连接（卡片）到（上一个）和（下一个）节点的所有关系

生成的密码查询可以细分为三个不同的部分。第一部分负责查找（存档）节点，给定（卡片）节点的ID：

最后，我们在归档队列的末尾插入（卡片）：

WITH theCard, theArchive
MATCH (theArchive)-[tat:TAIL_CARD]->(archiveTail)-[tp:PREV_CARD]->(archivePrevious)-[pt:NEXT_CARD]->(archiveTail) 
WITH theCard, theArchive, archiveTail, tp, pt, archivePrevious
CREATE (archiveTail)-[:PREV_CARD]->(theCard)-[:NEXT_CARD]->(archiveTail)
CREATE (theCard)-[:PREV_CARD]->(archivePrevious)-[:NEXT_CARD]->(theCard)
DELETE tp,pt
RETURN theCard

---

我希望你会觉得这最后一次编辑很有趣，因为我通过这个练习找到了工作。我想再次感谢韦斯（通过Twitter和堆栈溢出）在这个有趣的（至少对我来说）实验中提供的远程帮助。

您的解决方案似乎足够好，也符合您的目的。我只是给你提一些建议。。那个当你检查要存档的卡在列表中间时，确认它在中间，而不需要检查它是否在列表的头部或尾部，反之亦然。

< P>一个好问题——图中的双链表。我最近研究了一个类似的概念，需要跟踪列表，但试图找到一种方法来避免需要知道如何处理列表末尾边缘情况的困难。我努力的结果是

转换为双链接列表，如下所示：

CREATE
 (head:Head), 
 (tail:Tail),
 (head)-[:NEXT]->(tail),
 (tail)-[:PREV]->(head),
 (a:Archive)-[:NEXT]->(:ArchiveTail)-[:PREV]->(a);
; // we need something to start at, and an archive list

然后，您可以使用以下简单方法对节点进行排队：

MATCH (tail:Tail)-[p:PREV]->(prev),
      (tail)<-[n:NEXT]-(prev)
CREATE (new {text:"new card"})<-[:NEXT]-(prev),  
       (new)-[:PREV]->(prev),
       (new)<-[:PREV]-(tail),
       (new)-[:NEXT]->(tail) 
DELETE p, n

匹配（tail:tail）-[p:PREV]->（PREV），
（尾）（下），
（到存档）（下一个）-[：上一个]->（上一个）
删除nn、np、pn、pp
以拱形
匹配（存档：存档）-[n:下一个]->（第一个）-[p:上一个]->（存档）
CREATE（archive）-[：NEXT]->（toArchive）你可能应该用一些真实的数据在文章中创建一个图表摘要，这样每个人都可以看到数据是如何从你的查询中返回的？我们还有一些示例数据可供使用/测试。您可能有兴趣查看我的跳过列表图表要点。。。它处理空列表时有一个永远不会被删除的尾部和头部，所以情况总是一样的（删除一个内部节点）：@WesFreeman非常有趣。所以你把头部和尾部的概念从关系转移到了节点上，就像我刚才所做的那样。这确实让事情变得简单多了！非常聪明！
// first let's get a hold of the card we want to archive
MATCH (theCard:Card) WHERE ID(theCard)=44
// next, let's get a hold of the correspondent archive list node, since we need to move the card in that list
OPTIONAL MATCH (theCard)<-[:NEXT_CARD|HEAD_CARD*]-(theList:List)<-[:NEXT_LIST|HEAD_LIST*]-(theProject:Project)-[:ARCHIVE_LIST]->(theArchive:List)
// let's check if we are in the case where the card to be archived is in the middle of a list
OPTIONAL MATCH (before:Card)-[btc:NEXT_CARD]->(theCard:Card)-[tca:NEXT_CARD]->(after:Card) 
OPTIONAL MATCH (next:Card)-[ntc:PREV_CARD]->(theCard:Card)-[tcp:PREV_CARD]->(previous:Card) 
// let's check if the card to be archived is the only card in the list
OPTIONAL MATCH (listOfOne:List)-[lootc:TAIL_CARD]->(theCard:Card)<-[tcloo:HEAD_CARD]-(listOfOne:List)
// let's check if the card to be archived is at the head of the list
OPTIONAL MATCH (listToHead:List)-[lthtc:HEAD_CARD]->(theCard:Card)-[tcs:NEXT_CARD]->(second:Card)-[stc:PREV_CARD]->(theCard:Card) 
// let's check if the card to be archived is at the tail of the list
OPTIONAL MATCH (listToTail:List)-[ltttc:TAIL_CARD]->(theCard:Card)-[tcntl:PREV_CARD]->(nextToLast:Card)-[ntltc:NEXT_CARD]->(theCard:Card) 
WITH 
    theCard, theList, theProject, theArchive,
    CASE WHEN theArchive IS NULL THEN [] ELSE [(theArchive)] END AS archives,
    CASE WHEN before IS NULL THEN [] ELSE [(before)] END AS befores, 
    before, btc, tca, after, 
    CASE WHEN next IS NULL THEN [] ELSE [(next)] END AS nexts, 
    next, ntc, tcp, previous, 
    CASE WHEN listOfOne IS NULL THEN [] ELSE [(listOfOne)] END AS listsOfOne, 
    listOfOne, lootc, tcloo, 
    CASE WHEN listToHead IS NULL THEN [] ELSE [(listToHead)] END AS listsToHead, 
    listToHead, lthtc, tcs, second, stc, 
    CASE WHEN listToTail IS NULL THEN [] ELSE [(listToTail)] END AS listsToTail, 
    listToTail, ltttc, tcntl, nextToLast, ntltc
// let's handle the case in which the archived card was in the middle of a list
FOREACH (value IN befores | 
    CREATE (before)-[:NEXT_CARD]->(after)
    CREATE (after)-[:PREV_CARD]->(before)
    DELETE btc, tca)
FOREACH (value IN nexts | DELETE ntc, tcp)
// let's handle the case in which the archived card was the one and only card in the list
FOREACH (value IN listsOfOne | 
    CREATE (listOfOne)-[:HEAD_CARD]->(listOfOne)
    CREATE (listOfOne)-[:TAIL_CARD]->(listOfOne)
    DELETE lootc, tcloo)
// let's handle the case in which the archived card was at the head of the list
FOREACH (value IN listsToHead | 
    CREATE (listToHead)-[:HEAD_CARD]->(second)
    DELETE lthtc, tcs, stc)
// let's handle the case in which the archived card was at the tail of the list
FOREACH (value IN listsToTail | 
    CREATE (listToTail)-[:TAIL_CARD]->(nextToLast)
    DELETE ltttc, tcntl, ntltc)
// finally, let's move the card in the archive  
// first get a hold of the archive list to which we want to add the card
WITH 
    theCard, 
    theArchive
// first get a hold of the list to which we want to add the new card
OPTIONAL MATCH (theArchive)-[tact:TAIL_CARD]->(currentTail:Card)
// check if the list is empty
OPTIONAL MATCH (theArchive)-[tata1:TAIL_CARD]->(theArchive)-[tata2:HEAD_CARD]->(theArchive)
WITH
    theArchive, theCard,
    CASE WHEN currentTail IS NULL THEN [] ELSE [(currentTail)] END AS currentTails,
    currentTail, tact,
    CASE WHEN tata1 IS NULL THEN [] ELSE [(theArchive)] END AS emptyLists,
    tata1, tata2
// handle the case in which the list already had at least one card
FOREACH (value IN currentTails | 
    CREATE (theArchive)-[:TAIL_CARD]->(theCard)
    CREATE (theCard)-[:PREV_CARD]->(currentTail)
    CREATE (currentTail)-[:NEXT_CARD]->(theCard)
    DELETE tact)
// handle the case in which the list was empty
FOREACH (value IN emptyLists |
    CREATE (theArchive)-[:TAIL_CARD]->(theCard)
    CREATE (theArchive)-[:HEAD_CARD]->(theCard)
    DELETE tata1, tata2)
RETURN theCard

MATCH (theList:List)-[tlt:TAIL_CARD]->(tail)-[tp:PREV_CARD]->(previous)-[pt:NEXT_CARD]->(tail) 
WHERE ID(theList)={{listId}}
WITH theList, tail, tp, pt, previous
CREATE (newCard:Card { title: "Card Title", description: "" })
CREATE (tail)-[:PREV_CARD]->(newCard)-[:NEXT_CARD]->(tail)
CREATE (newCard)-[:PREV_CARD]->(previous)-[:NEXT_CARD]->(newCard)
DELETE tp,pt
RETURN newCard 

MATCH (theCard)<-[:NEXT_CARD|HEAD_CARD*]-(l:List)<-[:NEXT_LIST*]-(h)<-[:HEAD_LIST]-(p:Project)-[:ARCHIVE]->(theArchive:Archive) 
WHERE ID(theCard)={{cardId}}

WITH theCard, theArchive
MATCH (previous)-[ptc:NEXT_CARD]->(theCard)-[tcn:NEXT_CARD]->(next)-[ntc:PREV_CARD]->(theCard)-[tcp:PREV_CARD]->(previous)
WITH theCard, theArchive, previous, next, ptc, tcn, ntc, tcp
CREATE (previous)-[:NEXT_CARD]->(next)-[:PREV_CARD]->(previous)
DELETE ptc, tcn, ntc, tcp

WITH theCard, theArchive
MATCH (theArchive)-[tat:TAIL_CARD]->(archiveTail)-[tp:PREV_CARD]->(archivePrevious)-[pt:NEXT_CARD]->(archiveTail) 
WITH theCard, theArchive, archiveTail, tp, pt, archivePrevious
CREATE (archiveTail)-[:PREV_CARD]->(theCard)-[:NEXT_CARD]->(archiveTail)
CREATE (theCard)-[:PREV_CARD]->(archivePrevious)-[:NEXT_CARD]->(theCard)
DELETE tp,pt
RETURN theCard

CREATE
 (head:Head), 
 (tail:Tail),
 (head)-[:NEXT]->(tail),
 (tail)-[:PREV]->(head),
 (a:Archive)-[:NEXT]->(:ArchiveTail)-[:PREV]->(a);
; // we need something to start at, and an archive list

MATCH (tail:Tail)-[p:PREV]->(prev),
      (tail)<-[n:NEXT]-(prev)
CREATE (new {text:"new card"})<-[:NEXT]-(prev),  
       (new)-[:PREV]->(prev),
       (new)<-[:PREV]-(tail),
       (new)-[:NEXT]->(tail) 
DELETE p, n

MATCH (toArchive)-[nn:NEXT]->(next),
      (toArchive)<-[np:PREV]-(next),
      (toArchive)<-[pn:NEXT]-(prev),
      (toArchive)-[pp:PREV]->(prev) 
WHERE toArchive.text = "new card 2" 
CREATE (prev)-[:NEXT]->(next)-[:PREV]->(prev) 
DELETE nn, np, pn, pp 
WITH toArchive 
MATCH (archive:Archive)-[n:NEXT]->(first)-[p:PREV]->(archive) 
CREATE (archive)-[:NEXT]->(toArchive)<-[:PREV]-(first),
       (archive)<-[:PREV]-(toArchive)-[:NEXT]->(first) 
DELETE n, p