graphql-python/graphene-django

`select_related` and `prefetch_related`

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#57 opened on Nov 13, 2016

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Description

When I inspected the actual SQL queries being run against DB, I found that for foreignkey and manytomany relationships, we have the n+1 problem.

For example, suppose there are 5 teams, each with 11 members, this query:

query {
  teams {
    edges {
      node {
        members {
          edges {
            node {
              name
            }
          }
        }
      }
    }
  }
}

will result in 1 query for selecting teams, and 5 more queries for selecting members of each team. 6 queries in total.

Normally, we would do a query like this Team.objects.all().prefetch_related('members') to reduce to 2 queries.

I think it would be extremely beneficial if DjangoObjectType can detect special fields:

  • ForeignField
  • OneToOneField
  • OneToManyField
  • ManyToManyField and apply appropriate prefetch_related and/or select_related when such fields are present in graph queries.

Contributor guide

Tech stack
pythondjangographqlsql
Domain
backendapidatabase
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Django ORMGraphQL basicsPython
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the DjangoObjectType class in graphene django's types.py to understand how fields are resolved. Look for existing use of select related and prefetch related in the codebase. Examine the model's relationship fields (ForeignKey, OneToOneField, ManyToManyField) and design a mechanism to automatically apply these optimizations when the related fields are queried. Check the project's test suite to ensure no regressions. Consider using the info argument in resolvers to determine which fields are requested.