Hi,
The Neo4jClient now supports Cypher as a query language with Neo4j. However I noticed the following:
- Simple graph traversals are much more efficient when using Gremlin
- Queries in Gremlin are 30-50% faster for simple traversals
- Cypher is ideal for complex traversals where back tracking is required
- Cypher is our choice of query language for reporting
- Gremlin is our choice of query language for simple traversals where projections are not required
- Cypher has intrinsic table projection model, where Gremlins table projection model relies on AS steps which can be cumbersome when backtracking e.g. Back(), As() and _CopySplit, where cypher is just comma separated matches
- Cypher is much better suited for outer joins than Gremlin, to achieve similar results in gremlin requires parallel querying with CopySplit, where as in Cypher using the Match clause with optional relationships
- Gremlin is ideal when you need to retrieve very simple data structures
- Table projection in gremlin can be very powerful, however outer joins can be very verbose
So in a nutshell, we like to use Cypher when we need tabular data back from Neo4j and is especially useful in outer joins.
Here are two queries that return the exact same data from Neo4j, one in Cypher and one in Gremlin.
Cypher Report Query
var resultSet = graphClient.RootNode
.StartCypher("root")
.Match(@"root-[:HOSTS]->(agency)
<-[:USER_BELONGS_TO]-(user)-[:USER_LINKED_TO_PROGRAM]
->(program)
<-[:HAS_PROGRAM]-(centre),
(program)<-[:HAS_SUGGESTED_PROGRAM]-(referralDecisionsSection)
<-[:REFERRAL_HAS_DECISIONS_SECTION]-(referral)-[:CREATED_BY]
->(createdByUser), (referral)-[:REFERRAL_HAS_WHO_SECTION]
->(whoSection)-[:HAS_PARTICIPANT]->(participant)")
.Where<Agency>(agency => agency.Key == userIdentifier.AgencyKey)
.And()
.Where<User>(user => user.Username == userIdentifier.Username)
.And()
.Where<Referral>(referral => referral.Completed == false)
.Return((user, program, centre, createdByUser, referral, whoSection, participant) =>
new ReferralByGroup
{
UserFamilyName = createdByUser.As<User>().FamilyName,
UserGivenName = createdByUser.As<User>().GivenName,
Program = program.As<Program>().Name,
Centre = centre.As<Centre>().Name,
ReferralId = referral.As<Referral>().UniqueId,
ReferralDate = whoSection.As<ReferralWhoSection>().ReferralDate,
ParticipantName = participant.As<ReferralParticipant>().Name,
ParticipantDisplayOrder = participant.As<ReferralParticipant>().DisplayOrder,
})
.Results
.ToArray();
Gremlin Report Query using Table Projections
var resultSet = graphClient
.RootNode
.Out<Agency>(Hosts.TypeKey, a => a.Key == userIdentifier.AgencyKey)
.In<User>(UserBelongsTo.TypeKey, u => u.Username == userIdentifier.Username)
.Out<Program>(UserLinkedToProgram.TypeKey)
.As("Program")
.In<Centre>(HasProgram.TypeKey)
.As("Centre")
.BackV<Program>("Program")
.In<ReferralDecisionsSection>(HasSuggestedProgram.TypeKey)
.In<Referral>(ReferralHasDecisionsSection.TypeKey, r => r.Completed == false)
.As("ReferralId")
.Out<User>(CreatedBy.TypeKey)
.As("UserGivenName")
.As("UserFamilyName")
.BackV<Referral>("ReferralId")
.Out<ReferralWhoSection>(ReferralHasWhoSection.TypeKey)
.As("ReferralDate")
.Out<ReferralParticipant>(HasParticipant.TypeKey)
.As("ParticipantDisplayOrder")
.As("ParticipantName")
.Table
<ReferralByGroup, Program, Centre, Referral, User, User, ReferralWhoSection, ReferralParticipant,
ReferralParticipant>(
program => program.Name,
centre => centre.Name,
referral => referral.UniqueId,
user => user.FamilyName,
user => user.GivenName,
who => who.ReferralDate,
participant => participant.Name,
participant => participant.DisplayOrder
)
.ToArray();
Below is the converted parameterised script sent for cypher and gremlin respectively for those not familiar with the Neo4jClient.
Cypher
START root=node({p8})
MATCH root-[:HOSTS]->(agency)
<-[:USER_BELONGS_TO]-(user)-[:USER_LINKED_TO_PROGRAM]->(program)
<-[:HAS_PROGRAM]-(centre),
(program)<-[:HAS_SUGGESTED_PROGRAM]-(referralDecisionsSection)
<-[:REFERRAL_HAS_DECISIONS_SECTION]-(referral)-[:CREATED_BY]
->(createdByUser), (referral)-[:REFERRAL_HAS_WHO_SECTION]
->(whoSection)-[:HAS_PARTICIPANT]
->(participant)
WHERE (agency.Key? = {p0}) AND (user.Username? = {p1}) AND (referral.Completed? = {p2})
RETURN createdByUser.FamilyName? AS UserFamilyName, createdByUser.GivenName? AS UserGivenName, program.Name? AS Program, centre.Name? AS Centre, referral.UniqueId? AS ReferralId, whoSection.ReferralDate? AS ReferralDate, participant.Name? AS ParticipantName, participant.DisplayOrder? AS ParticipantDisplayOrder
Gremlin
g.v(p0)
.out(p1).filter{ it[p2].equalsIgnoreCase(p3) }
.in(p4).filter{ it[p5].equalsIgnoreCase(p6) }
.out(p7).as(p8).in(p9).as(p10).back(p11)
.in(p12).in(p13).filter{ it[p14] == p15 }.as(p16)
.out(p17).as(p18).as(p19).back(p20)
.out(p21).as(p22).out(p23).as(p24).as(p25)
.table(new Table()){it[p26]}{it[p27]}{it[p28]}{it[p29]}{it[p30]}{it[p31]}{it[p32]}{it[p33]}
.cap
I have included below the non-paramerterised cypher and gremlin query respectively.
Cypher
START root=node(0) MATCH root-[:HOSTS]->(agency)<-[:USER_BELONGS_TO]-(user)-[:USER_LINKED_TO_PROGRAM] ->(program) <-[:HAS_PROGRAM]-(centre),(program) <-[:HAS_SUGGESTED_PROGRAM]-(referralDecisionsSection) <-[:REFERRAL_HAS_DECISIONS_SECTION]-(referral)-[:CREATED_BY]->(createdByUser), (referral)-[:REFERRAL_HAS_WHO_SECTION] ->(whoSection)-[:HAS_PARTICIPANT] ->(participant) WHERE (agency.Key? = romikoagency) AND (user.Username? = romiko.derbynew) AND (referral.Completed? = false) RETURN createdByUser.FamilyName? AS UserFamilyName, createdByUser.GivenName? AS UserGivenName, program.Name? AS Program, centre.Name? AS Centre, referral.UniqueId? AS ReferralId, whoSection.ReferralDate? AS ReferralDate, participant.Name? AS ParticipantName, participant.DisplayOrder? AS ParticipantDisplayOrder
Gremlin
g.v('0').out('HOSTS').filter{ it['Key'].equalsIgnoreCase('romikoagency') }
.in('USER_BELONGS_TO').filter{ it['Username'].equalsIgnoreCase('romiko.derbynew') }
.out('USER_LINKED_TO_PROGRAM').as('Program')
.in('HAS_PROGRAM').as('Centre').back('Program')
.in('HAS_SUGGESTED_PROGRAM')
.in('REFERRAL_HAS_DECISIONS_SECTION').filter{ it['Completed'] == false }.as('ReferralId')
.out('CREATED_BY').as('UserGivenName').as('UserFamilyName').back('ReferralId')
.out('REFERRAL_HAS_WHO_SECTION').as('ReferralDate')
.out('HAS_PARTICIPANT').as('ParticipantDisplayOrder').as('ParticipantName')
.table(new Table()){it['Name']}{it['Name']}{it['UniqueId']}{it['FamilyName']}{it['GivenName']}{it['ReferralDate']}{it['Name']}{it['DisplayOrder']}.cap
Romiko Derbynew 