Neo4j.rb -不能使用

Question

我有3983个BISAC类型的节点。我不能用order by来取回它们。以下是起作用的因素：

irb(main):024:0* bc = Bisac.all
=> <QueryProxy  CYPHER: "MATCH (n:`Bisac`)">
irb(main):025:0> bc.count
 CYPHER 796ms MATCH (n:`Bisac`) RETURN count(n) AS n 
=> 3983
irb(main):026:0> bc.first
 CYPHER 129ms MATCH (n:`Bisac`) RETURN n ORDER BY n.uuid LIMIT {limit_1} | {:limit_1=>1}
=> #<Bisac uuid: "d1c60f13-3c70-11e5-8eb8-22000b18b199", bisac_code: "MUS037050", bisac_value: "MUSIC / Printed Music / Mixed Collections">
irb(main):027:0> bc.last
 CYPHER 127ms MATCH (n:`Bisac`) RETURN n ORDER BY n.uuid LIMIT {limit_1} | {:limit_1=>1}
=> #<Bisac uuid: "d1c60f13-3c70-11e5-8eb8-22000b18b199", bisac_code: "MUS037050", bisac_value: "MUSIC / Printed Music / Mixed Collections">

当尝试使用order时，它会像这样失败：

irb(main):033:0* bc = Bisac.order('bisac_code')
=> <QueryProxy  CYPHER: "MATCH (result_bisac:`Bisac`) ORDER BY bisac_code">
irb(main):034:0> bc.count
 CYPHER 790ms MATCH (result_bisac:`Bisac`) RETURN count(result_bisac) AS result_bisac 
=> 3983
irb(main):035:0> bc.first
 CYPHER 364ms MATCH (result_bisac:`Bisac`) WITH result_bisac ORDER BY bisac_code RETURN HEAD(COLLECT(result_bisac)) as result_bisac 
Neo4j::Session::CypherError: bisac_code not defined (line 1, column 57 (offset: 56))
"MATCH (result_bisac:`Bisac`) WITH result_bisac ORDER BY bisac_code RETURN HEAD(COLLECT(result_bisac)) as result_bisac"
                                                         ^
    from /Users/levi/.rbenv/versions/2.2.1/lib/ruby/gems/2.2.0/gems/neo4j-core-5.0.10/lib/neo4j-server/cypher_response.rb:211:in `raise_cypher_error'

这里怎么了？

我的宝石是: neo4j (5.0.14)新4j-核心(5.0.10)

Answer 1

耶，我可以马上解释的事情！)

因此，计数中没有ORDER BY的原因是，它只会减慢您的count，并且永远不会返回不同的结果。

至于.order，原因是您传递的是String而不是Symbol。因为Cypher是一种比SQL更动态的查询语言，所以我曾经决定将字符串和符号区别对待。这样做的想法是，如果您指定一个字符串，您可能需要指定一个更动态的ORDER BY子句，而通常您将使用一个符号来指定要排序的属性。这实际上是在来自Query的neo4j-core API中实现的，但它会影响neo4j gem中的ActiveNode。

所以答案是：

bc = Bisac.order(:bisac_code)

bc.first

尽管如此，这确实应该被记录下来，并且有可能变得更聪明。我会创造一个问题的，谢谢！