feat: add optional argument for plural attributes

[igdianov]

This PR adds support for default optional: true argument for collections in the query selection graph, i.e.

query {
  Authors {
    select {
      id
      name
      books(optional: true) {
        id
        title
        genre
      }
    }
  }
}

With optional: true, the data fetcher will apply LEFT OUTER JOIN on books and return empty books collections:

{
  "data": {
    "Authors": {
      "select": [
        {
          "id": 1,
          "name": "Leo Tolstoy",
          "books": [
            {
              "id": 2,
              "title": "War and Peace",
              "genre": "NOVEL"
            },
            {
              "id": 3,
              "title": "Anna Karenina",
              "genre": "NOVEL"
            }
          ]
        },
        {
          "id": 4,
          "name": "Anton Chekhov",
          "books": [
            {
              "id": 5,
              "title": "The Cherry Orchard",
              "genre": "PLAY"
            },
            {
              "id": 6,
              "title": "The Seagull",
              "genre": "PLAY"
            },
            {
              "id": 7,
              "title": "Three Sisters",
              "genre": "PLAY"
            }
          ]
        },
        {
          "id": 8,
          "name": "Igor Dianov",
          "books": []
        }
      ]
    }
  }
}

Use optional: false to enforce INNER JOIN, so that

query {
  Authors {
    select {
      id
      name
      books(optional: false) {
        id
        title
        genre
      }
    }
}

Will return entity graph with only existing associations:

{
  "data": {
    "Authors": {
      "select": [
        {
          "id": 1,
          "name": "Leo Tolstoy",
          "books": [
            {
              "id": 2,
              "title": "War and Peace",
              "genre": "NOVEL"
            },
            {
              "id": 3,
              "title": "Anna Karenina",
              "genre": "NOVEL"
            }
          ]
        },
        {
          "id": 4,
          "name": "Anton Chekhov",
          "books": [
            {
              "id": 5,
              "title": "The Cherry Orchard",
              "genre": "PLAY"
            },
            {
              "id": 6,
              "title": "The Seagull",
              "genre": "PLAY"
            },
            {
              "id": 7,
              "title": "Three Sisters",
              "genre": "PLAY"
            }
          ]
        }
      ]
    }
  }
}

You can also configure default join fetch optional argument value via Api.

[codecov]

Codecov Report

Merging #138 into master will decrease coverage by 0.04%.
The diff coverage is 76.92%.

@@             Coverage Diff              @@
##             master     #138      +/-   ##
============================================
- Coverage     68.27%   68.23%   -0.05%     
- Complexity      432      437       +5     
============================================
  Files            33       33              
  Lines          2219     2238      +19     
  Branches        330      331       +1     
============================================
+ Hits           1515     1527      +12     
- Misses          571      576       +5     
- Partials        133      135       +2

Impacted Files	Coverage Δ	Complexity Δ
...res/graphql/jpa/query/schema/model/book/Genre.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...a/query/schema/impl/QraphQLJpaBaseDataFetcher.java	71.45% <100%> (+0.05%)	144 <2> (ø)	⬇️
...query/schema/impl/GraphQLJpaSimpleDataFetcher.java	91.3% <100%> (ø)	7 <1> (ø)	⬇️
...query/autoconfigure/GraphQLJpaQueryProperties.java	84.61% <50%> (-6.3%)	12 <1> (+1)
.../query/schema/impl/GraphQLJpaQueryDataFetcher.java	92.63% <50%> (-1.06%)	24 <0> (+1)
...jpa/query/schema/impl/GraphQLJpaSchemaBuilder.java	87.65% <72.72%> (-0.41%)	119 <0> (ø)
...ry/schema/impl/GraphQLJpaOneToManyDataFetcher.java	73.84% <81.81%> (+0.16%)	15 <3> (+2)	⬆️
...hql/jpa/query/schema/impl/JpaPredicateBuilder.java	52.22% <0%> (+0.4%)	56% <0%> (+1%)	⬆️

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[igdianov]

@molexx ^^^^^

I understand why you need left outer joins, so I added optional argument for plural attributes. May be default optional should be configurable via Builder Api?

[molexx]

Aha, this is great, thanks!

Yes works ok.

Allowing the optionals by default is good for me, I haven't had to add it in the query or make an API call. Adding to the builder would keep consistency with 'distinct'.