fix: build join fetch from selection graph

[igdianov]

This PR builds a join fetch graph from query selection tree to avoid Hibernate error: query specified join fetching, but the owner of the fetched association was not present in the select list

Given the following query:

{
  Humans(where: {
    friends: {
      name: {LIKE: "R2-D2"}
    }, 
    favoriteDroid: {
      primaryFunction: {
        function: {EQ: "Protocol"}
      }
    }
  }) {
    select {
      id
      name
      homePlanet
      favoriteDroid {
        name
        primaryFunction {
          function
        }
      }
      friends {
        name
        friends {
          name
        }
      }
    }
  }
}

The builder will traverse the selection graph to apply an explicit fetch join for each relation, after that it will reuse existing joins to apply where search criteria expressions.

As a result the query will create a fetch join for each relation in the selection to fetch the related data and add where criteria restrictions to another fetch join to avoid filtering graph collections, i.e.

query {
  Authors(where: {
    books: {
      title: {LIKE: "War"}
    }
  }) {
    select {
      id
      name
      books {
        id
        title
        genre
      }
    }
  }
}

The following JPQL query will be created with extra fetch join to retrieve full books collection:

select distinct Author from Author as Author 
    inner join fetch Author.books as generatedAlias0 
    inner join fetch Author.books as generatedAlias1 
    where lower(generatedAlias0.title) like :param0 
    order by Author.id asc

The result books collection containing book with title LIKE "War" will not be filtered:

{
  "data": {
    "Authors": {
      "select": [
        {
          "id": 1,
          "name": "Leo Tolstoy",
          "books": [
            {
              "id": 2,
              "title": "War and Peace",
              "genre": "NOVEL"
            },
            {
              "id": 3,
              "title": "Anna Karenina",
              "genre": "NOVEL"
            }
          ]
        }
      ]
    }
  }
}

If you omit books in the selection, i.e.

  Authors(where: {
    books: {
      title: {LIKE: "War"}
    }
  }) {
    select {
      id
      name
      # books {
      #   id
      #   title
      #   genre
      # }
    }
  }
}

The JPQL query will not contain extra fetch join for books:

select distinct Author from Author as Author 
   inner join fetch Author.books as generatedAlias0 
   where lower(generatedAlias0.title) like :param0 
   order by Author.id asc

And the result:

{
  "data": {
    "Authors": {
      "select": [
        {
          "id": 1,
          "name": "Leo Tolstoy"
        }
      ]
    }
  }
}

[codecov]

Codecov Report

Merging #137 into master will increase coverage by 0.12%.
The diff coverage is 89.28%.

@@             Coverage Diff              @@
##             master     #137      +/-   ##
============================================
+ Coverage     68.15%   68.27%   +0.12%     
- Complexity      428      432       +4     
============================================
  Files            33       33              
  Lines          2201     2219      +18     
  Branches        325      330       +5     
============================================
+ Hits           1500     1515      +15     
- Misses          569      571       +2     
- Partials        132      133       +1

Impacted Files	Coverage Δ	Complexity Δ
...a/query/schema/impl/QraphQLJpaBaseDataFetcher.java	71.39% <100%> (+0.26%)	144 <4> (+1)	⬆️
...hql/jpa/query/schema/impl/JpaPredicateBuilder.java	51.82% <75%> (+1.18%)	55 <0> (+3)	⬆️

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