fix: Apply left outer join to retrieve optional associations [WIP]

[igdianov]

This PR fixes #101

Given optional to-one association, i.e. favoriteDroid:

@Entity(name = "Human")
@Data
@EqualsAndHashCode(callSuper=true)
public class Human extends Character {

    String homePlanet;

    @ManyToOne(fetch = FetchType.LAZY, optional = true)
    @JoinColumn(name = "favorite_droid_id")
    Droid favoriteDroid;

}

The GraphQL schema will generate optional argument with default value derived from JPA's optional attribute value definition.

Type Humans {
   ...
   favoriteDroid(where: DroidsCriteriaExpression, optional: Boolean = true): Droid
   ...
}

The JPQL query will now apply left outer join to all queries against entity graph with optional associations, i.e. given the following query

    Humans {
        select {
            id
            name
            homePlanet
            favoriteDroid {
              name
            }
        }
    }

And return all records with optional favoriteDroid association null value

{
  "data": {
    "Humans": {
      "select": [
        {
          "id": "1000",
          "name": "Luke Skywalker",
          "homePlanet": "Tatooine",
          "favoriteDroid": {
            "name": "C-3PO"
          }
        },
        {
          "id": "1001",
          "name": "Darth Vader",
          "homePlanet": "Tatooine",
          "favoriteDroid": {
            "name": "R2-D2"
          }
        },
        {
          "id": "1002",
          "name": "Han Solo",
          "homePlanet": null,
          "favoriteDroid": null
        },
        {
          "id": "1003",
          "name": "Leia Organa",
          "homePlanet": "Alderaan",
          "favoriteDroid": null
        },
        {
          "id": "1004",
          "name": "Wilhuff Tarkin",
          "homePlanet": null,
          "favoriteDroid": null
        }
      ]
    }
  }
}

It will possible to override optional strategy with explicit value, i.e.

query {
  Humans {
    select {
      id
      name
      homePlanet
      favoriteDroid(optional: false) {
        name
      }
    }
  }
}

Will return the following result:

{
  "data": {
    "Humans": {
      "select": [
        {
          "id": "1000",
          "name": "Luke Skywalker",
          "homePlanet": "Tatooine",
          "favoriteDroid": {
            "name": "C-3PO"
          }
        },
        {
          "id": "1001",
          "name": "Darth Vader",
          "homePlanet": "Tatooine",
          "favoriteDroid": {
            "name": "R2-D2"
          }
        }
      ]
    }
  }
}

[codecov]

Codecov Report

Merging #105 into master will increase coverage by 0.09%.
The diff coverage is 75%.

@@             Coverage Diff              @@
##             master     #105      +/-   ##
============================================
+ Coverage     65.73%   65.83%   +0.09%     
- Complexity      366      369       +3     
============================================
  Files            37       37              
  Lines          2014     2014              
  Branches        296      296              
============================================
+ Hits           1324     1326       +2     
  Misses          562      562              
+ Partials        128      126       -2

Impacted Files	Coverage Δ	Complexity Δ
...a/query/schema/impl/QraphQLJpaBaseDataFetcher.java	72.64% <75%> (+0.58%)	114 <0> (+3)	⬆️

---

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[codecov]

Codecov Report

Merging #105 into master will increase coverage by 0.58%.
The diff coverage is 83.6%.

@@            Coverage Diff             @@
##             master   #105      +/-   ##
==========================================
+ Coverage     66.42%    67%   +0.58%     
- Complexity      383    400      +17     
==========================================
  Files            34     33       -1     
  Lines          2031   2061      +30     
  Branches        301    304       +3     
==========================================
+ Hits           1349   1381      +32     
- Misses          552    555       +3     
+ Partials        130    125       -5

Impacted Files	Coverage Δ	Complexity Δ
...ures/graphql/jpa/query/schema/model/book/Book.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...graphql/jpa/query/schema/model/starwars/Droid.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...jpa/query/schema/impl/GraphQLJpaSchemaBuilder.java	88.05% <100%> (+0.75%)	119 <6> (+4)	⬆️
...a/query/schema/impl/QraphQLJpaBaseDataFetcher.java	73.75% <76.19%> (+0.68%)	130 <12> (+13)	⬆️

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[molexx]

Thanks for this! We've been running against this branch for a few days, the fix works as expected and we haven't noticed any unexpected side effects.

[igdianov]

@molexx Thank you for checking. I will refactor and apply optional association fetching after merging PR to support nested associations in where criteria expressions.

[molexx]

Thanks! :-)

[molexx]

I don't think this is working properly in the merge to master. I've had difficulty proving when it broke because the branch this was on is now deleted and I've not had much success trying to pull builds for commits noted above from jitpack.

I'll continue to investigate tomorrow...

[molexx]

Our project works in the old build from that branch but does not work with 0.3.25, yet doing a similar query with the starwars schema using the example project works fine with master.

@igdianov are there any changes to this outer join functionality between the branch and master? Did you implement the optional keyword you mentioned? I can't see any changes to the example project or starwars schema to support this? Thanks!

[igdianov]

@molexx I had restored igdianov-use-left-outer-join-original branch so you could try to use it again and compare generated queries between initial and later commits in igdianov-use-left-outer-join.

I have made the changes only to apply left outer join for @ManyToOne and @OneToOne singular attributes. I did not make any changes to Startwars schema because JPA annotation optional attribute is true by default.

[igdianov]

@molexx Let me know what you find. Thank you

[molexx]

@igdianov thanks for restoring the branches!

c7754eb works OK whereas a6761b46 does not. The JPQL is as expected - when it works there's a left outer join between the tables whereas when it doesn't there's an inner join.

The parent entity contains a HashSet of the child records with @OneToMany(fetch = FetchType.LAZY, mappedBy=<id of parent in child>).

[igdianov]

@molexx I need to understand the full context of query to be able to find the solution. The changes that work for you use outer join for all associations, but it is not a good practice for performance reasons. Let me know more details...

[igdianov]

@molexx See #138 that adds supports for optional join fetch argument for collection attributes