Fixes #295: Querying interface @relation fields with non-unique relationship names

[michaeldgraham]

Issue #295 resulted from no label being added to the Cypher path pattern for related nodes being matched when querying an interface type @relation field. To make the path pattern more specific and prevent matching inappropriate nodes, the interface type name is now added as a label.

For example, given the following schema:

interface Tools {
  id: ID
}
type Screwdriver implements Tools {
  id: ID
  size: Int!
}
type Material {
  id: ID!
}
type Product {
  materials: [Material!]! @relation(name: "USES", direction: OUT)
  tools: [Tools!]! @relation(name: "USES", direction: OUT)
}

And this query over the tools interface type @relation field:

query {
  Product {
    tools {
      id
    }
  }
}

Current translation:

MATCH (`product`:`Product`) RETURN `product` {tools: [(`product`)-[:`USES`]->(`product_tools`) | product_tools {FRAGMENT_TYPE: head( [ label IN labels(product_tools) WHERE label IN $Tools_derivedTypes ] ),  .id }] } AS `product`

Translation with the fix:

MATCH (`product`:`Product`) RETURN `product` {tools: [(`product`)-[:`USES`]->(`product_tools`:`Tools`) | product_tools {FRAGMENT_TYPE: head( [ label IN labels(product_tools) WHERE label IN $Tools_derivedTypes ] ),  .id }] } AS `product`

In this translation, tools: [(`product`)-[:`USES`]->(`product_tools`) becomes tools: [(`product`)-[:`USES`]->(`product_tools`:`Tools`).

[codecov-io]

Codecov Report

Merging #366 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #366   +/-   ##
======================================
  Coverage    96.3%   96.3%           
======================================
  Files          24      24           
  Lines        2844    2844           
======================================
  Hits         2739    2739           
  Misses        105     105

Impacted Files	Coverage Δ
src/translate.js	98.31% <ø> (ø)	⬆️

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