我对通过密码创建关系的方式感到困惑。我的印象是 _src-[:likes]- _dst 创建了双向关系,但看起来情况并非如此,因为_src-[:likes]- _dst == _src<-[:likes]- _dst(下面提供的示例)
假设我创建了以下图表,但使用 _src[:likes] - _dst 表示法(使用'-'而不是'->')
create
(_u1 {type:"User",`name`:"u1",userId:'u1' }) , ( _u2 {type:"User",`name`:"u2",userId:'u2'} ) , ( _u3 {type:"User",`name`:"u3",userId:'u3' }) , ( _u4 {type:"User",`name`:"u4",userId:'u4' }) , ( _u5 {type:"User",`name`:"u5",userId:'u5'}) , (_u6 {type:"User",`name`:"u6",userId:'u6'}),
(_f1 {type:"Item",`name`:"f1",itemId:'f1' }) , ( _f2 {type:"Item",`name`:"f2",itemId:'f2' }) , ( _f3 {type:"Item",`name`:"f3",itemId:'f3' }) , ( _f4 {type:"Item",`name`:"f4",itemId:'f4'}) , (_f5 {type:"Item",`name`:"f5",itemId:'f5'}),
_u1-[:`likes`{likeValue:3}]-_f1 , _u1-[:`likes` {likeValue:13}]-_f2 , _u1-[:`likes` {likeValue:1}]-_f3 , _u1-[:`likes` {likeValue:5}]-_f4,
_u2-[:`likes`{likeValue:7}]-_f1 , _u2-[:`likes` {likeValue:13}]-_f2 , _u2-[:`likes` {likeValue:1}]-_f3,
_u3-[:`likes`{likeValue:5}]-_f1 , _u3-[:`likes` {likeValue:8}]-_f2 , _u4-[:`likes`{likeValue:5}]-_f1
,_u5-[:`likes` {likeValue:8}]-_f2,_u6-[:`likes` {likeValue:8}]-_f2;
我的印象是这样,你告诉 neo4j 创建一个双向关系。现在,看看下面的查询
neo4j-sh (?)$ start n=node(*) match n-[:likes]->m where has(n.type) and n.type='User' return n,m;
==> +-------+
==> | n | m |
==> +-------+
==> +-------+
==> 0 row
但相反的工作
neo4j-sh (?)$ start n=node(*) match n-[r]->m where has(n.type) and n.type="Item" return n,m limit 3;
==> +-----------------------------------------------------------------------------------------+
==> | n | m |
==> +-----------------------------------------------------------------------------------------+
==> | Node[7]{type:"Item",name:"f1",itemId:"f1"} | Node[4]{type:"User",name:"u4",userId:"u4"} |
==> | Node[7]{type:"Item",name:"f1",itemId:"f1"} | Node[3]{type:"User",name:"u3",userId:"u3"} |
==> | Node[7]{type:"Item",name:"f1",itemId:"f1"} | Node[2]{type:"User",name:"u2",userId:"u2"} |
==> +-----------------------------------------------------------------------------------------+
问题是为什么 a-[:likes]-b = a<-[:likes]-b ?
现在我按照 Cypher 手册中的说明再创建两个节点和一个关系
create (_u7 {type:"User",`name`:"u7",userId:'u7' });
create (_f7 {type:"Item",`name`:"f7",itemId:'f7' });
start src=node(*),dst=node(*) where src.name='u7' and dst.name='f7' create src-[:likes{likeValue:3}]-dst;
neo4j-sh (?)$ start n=node(*) match n-[r]->m where has(n.type) and n.type="User" return n,m limit 3;
==> +-------+
==> | n | m |
==> +-------+
==> +-------+
==> 0 row
同样的结果,我们不能从用户查询到项目,但
如果使用以下方法,我们现在可以从项目到用户,情况发生变化
create (_u {type:"User",`name`:"u8",userId:'u8' }) , ( _f {type:"User",`name`:"f8",userId:'f8'} ), _u-[:likes{likeValue:2}]-_f;
neo4j-sh (?)$ start n=node(*) match n-[r]->m where has(n.type) and n.type="User" return n,m limit 3;
==> +-------------------------------------------------------------------------------------------+
==> | n | m |
==> +-------------------------------------------------------------------------------------------+
==> | Node[19]{type:"User",name:"f8",userId:"f8"} | Node[18]{type:"User",name:"u8",userId:"u8"} |
==> +-------------------------------------------------------------------------------------------+
到底是怎么回事?这些是我的问题
1- 为什么创建 _src-[:likes]-_dst 不会创建双向关系?
2-如果不能,那为什么还要允许 _src-[:likes]-_dst 建立关系?为什么不强迫人们在建立关系时使用方向?
3- 我用来建立关系的两种方法有什么区别?( u7-f7和u8-f8 )