Environment

  • AgensGraph v2.0 release
  • CentOS 7

Situation

  • If you use MATCH to query a target when you use the create statement, but do not consider the edges, you can have duplicated edges between vertices.
  • e.g
-- Expected results
agens=# MATCH (a:person)-[r]->(b:person)
WHERE a.name='jhs'
AND b.name = 'hsjeon'
RETURN a,r,b;
              a               |              r              |                b
------------------------------+-----------------------------+---------------------------------
 person[4.517]{"name": "jhs"} | knows[11.15][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 
 
MATCH (a:person)-[r]->(b:person)
WHERE a.name='jhs'
AND b.name = 'hsjeon' 
-- If you do not have this part -- AND NOT EXISTS ((a)-[]->(b))
CREATE (a)-[:knows]->(b);


agens=# MATCH (a:person)-[r]->(b:person)
WHERE a.name='jhs'
AND b.name = 'hsjeon' AND NOT EXISTS ((a)-[]->(b))
CREATE (a)-[:knows]->(b)
;
GRAPH WRITE (INSERT VERTEX 0, INSERT EDGE 0)
agens=# MATCH (a:person)-[r]->(b:person)
WHERE a.name='jhs'
AND b.name = 'hsjeon'
CREATE (a)-[:knows]->(b)
;
GRAPH WRITE (INSERT VERTEX 0, INSERT EDGE 1)
agens=# MATCH (a:person)-[r]->(b:person)
WHERE a.name='jhs'
AND b.name = 'hsjeon'
CREATE (a)-[:knows]->(b)
;
GRAPH WRITE (INSERT VERTEX 0, INSERT EDGE 2)
agens=# MATCH (a:person)-[r]->(b:person)
WHERE a.name='jhs'
AND b.name = 'hsjeon'
CREATE (a)-[:knows]->(b)
;
GRAPH WRITE (INSERT VERTEX 0, INSERT EDGE 4)
agens=# MATCH (a:person)-[r]->(b:person)
WHERE a.name='jhs'
AND b.name = 'hsjeon'
CREATE (a)-[:knows]->(b)
;
GRAPH WRITE (INSERT VERTEX 0, INSERT EDGE 8)
agens=# MATCH (a:person)-[r]->(b:person)
WHERE a.name='jhs'
AND b.name = 'hsjeon'
CREATE (a)-[:knows]->(b)
;
GRAPH WRITE (INSERT VERTEX 0, INSERT EDGE 16)
agens=# MATCH (a:person)-[r]->(b:person)
WHERE a.name='jhs'
AND b.name = 'hsjeon'
CREATE (a)-[:knows]->(b)
;
GRAPH WRITE (INSERT VERTEX 0, INSERT EDGE 32)

agens=# MATCH (a:person)-[r]->(b:person) WHERE a.name = 'jhs' AND b.name = 'hsjeon' RETURN a,r,b;
              a               |              r              |                b
------------------------------+-----------------------------+---------------------------------
 person[4.517]{"name": "jhs"} | knows[11.15][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.29][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.30][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.31][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.32][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.33][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.34][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.35][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.36][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.37][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.38][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.39][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.40][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.41][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.42][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.43][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.44][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.45][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.46][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.47][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.48][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 person[4.517]{"name": "jhs"} | knows[11.49][4.517,4.546]{} | person[4.546]{"name": "hsjeon"}
 ....
 (64 rows)

solution

agens=# MATCH (a:person)-[r:knows]->(b:person)
agens-# WHERE a.name = 'jhs' AND b.name = 'hsjeon'
agens-# WITH id(a) AS a_id ,id(b) AS b_id, collect(id(r)) as rel_a_b
agens-# WITH collect(rel_a_b[0]) as c1
agens-# MATCH (a1:person)-[r1:knows]->(b1:person)
agens-# WHERE a1.name = 'jhs' AND b1.name = 'hsjeon'
agens-# AND NOT to_jsonb(id(r1))  IN c1
agens-# DELETE r1;
GRAPH WRITE (DELETE VERTEX 0, DELETE EDGE 63)