node.js - gremlin create edge while satisfying multiplicity constraint,if violated drop existing edge then create else just create it -

i struggling quite time solve problem like

i have graph in there defined multiplicity constraints . when new edge being created either new edge can created or can violate multiplicity constraint due data being changed.

now when data has changed need delete/drop existing edge , create new one. problem. not able drop , create edge in single go.

what have been trying sending query gremlin server via node-gremlin module of nodejs. relation trying create [merchant]-1--(sells)--*-> [product] . in given scenario 1 merchant can sell product . when other merchant starts selling product. need update reflect new relation between them. may case no 1 selling new edge has created. created edge returned.

29 jun 13:41:04 - [error: edge given label exists on in-vertex , label [sells] in-unique (error 597)] 29 jun  13:41:04 - { text: 'g.v().has(sidkey,sidval).ine(edgelabel).drop();graph.tx().commit();g.v().has(fidkey,fidval).oute(edgelabel).inv().has(sidkey,sidval).trynext().orelseget{g.v().has(fidkey,fidval).next().addedge(edgelabel,g.v().has(sidkey,sidval).next());};',      params:        { fidkey: 'merchant_id',          fidval: 20230,          sidkey: 'product_id',          sidval: 184504,          edgelabel: 'sells' } } 

the flow ii trying achieve this

find if existing edge present -> delete existing edge -> commit delete edge command --> create new edge --> commit new edge.

in above query have not written commit statement add edge because committing add edges in bulk.

i not able figure out how proceed solve problem . great.

you need iterate() on drop operation before committing transaction.

g.v().has(sidkey,sidval).ine(edgelabel).drop().iterate(); graph.tx().commit(); 

this common stumbling block , has been discussed previously: gremlin drop() isn't working via java api