WebWallet Graphstore

Transaction clearing microservice for the WebWallet API.

Contents

• Graph Database
• Data Modeling
• Query Design

Graph Database

Neo4j

• Cypher

Data Modeling

Nodes

Labels: IOU, Address, Currency, Transaction, Outputs.

• IOU
• Address
• Currency
• Transaction
  A transaction is a document, not an operation. Inserting a Transaction node is not equivalent to executing a transaction, which involves creating other nodes and relationships as well.
  • Outputs

Relationships

Types: Funds, Spends, Points.

• Clearing
  • IOUs
  • Outputs
• Indexing
  • Outputs

Constraints

Nodes with Address labels must satisfy the id property uniqueness constraint. Since Transaction nodes will be retrieved through traversals starting at Address nodes using their Outputs node (manual index), no constraint is imposed on Transaction node IDs in order to prevent a potentially large index from being created automatically by the database.

CREATE CONSTRAINT ON (address:Address) ASSERT address.id IS UNIQUE

Since uniqueness contraints cannot be created on relationships, CREATE UNIQUE must be used in combination with previous checks in order to manually enforce unique relationships on nodes.

...
WHERE NOT (txo)<-[:Spends {id:0}]-()
CREATE UNIQUE (txo)<-[s:Spends {id: 0}]-(txn)
...

Relationships with Spends labels should satisfy the id property existence constraint [enterprise edition feature]. Since Transaction documents contain outputs that can be referenced by subsequent transactions for clearing purposes, every Transaction that Spends another Transaction must specify which output it is referencing/spending.

CREATE CONSTRAINT ON ()-[output:Spends]-() ASSERT exists(output.id)

Query Design

Clearing

• Output Spending

MATCH (txo:Transaction)
WHERE txo.id = {transactionId}
SET txo.lock = true
WITH txo
WHERE NOT (txo)<-[:Spends {id:{outputId}}]-()
CREATE UNIQUE (txo)<-[:Spends {id: {outputId}}]-(txn:Transaction)
REMOVE txo.lock
RETURN txo, txn