Modelling one-to-many table relationships¶

Table of contents

Introduction
Step 1: Set up a table relationship in the database
Step 2: Set up GraphQL relationships
Step 3: Query using relationships

Introduction¶

A one-to-many relationship between two tables can be established via a foreign key constraint.

Say we have the following two tables in our database schema:

author (
  id SERIAL PRIMARY KEY,
  name TEXT
)

article (
  id SERIAL PRIMARY KEY,
  author_id INT
  title TEXT
  ...
)

These two tables are related via a one-to-many relationship. i.e:

an author can have many articles
an article has one author

Step 1: Set up a table relationship in the database¶

This one-to-many relationship can be established in the database by:

Adding a foreign key constraint from the article table to the author table using the author_id and id columns of the tables respectively.

This will ensure that the value of author_id column in the article table is present in the id column of the author table.

Step 2: Set up GraphQL relationships¶

To access the nested objects via the GraphQL API, create the following relationships:

Array relationship, articles from author table using article :: author_id -> id
Object relationship, author from article table using author_id -> author :: id

Step 3: Query using relationships¶

We can now:

fetch a list of authors with their articles:

 
query {
  author {
    id
    name
    articles {
      id
      title
    }
  }
}

Variables

​x
 
​

xxxxxxxxxx
 
{  "data": {    "author": [      {        "id": 1,        "name": "Justin",        "articles": [          {            "id": 15,            "title": "vel dapibus at"          },          {            "id": 16,            "title": "sem duis aliquam"          }        ]      },      {        "id": 2,        "name": "Beltran",        "articles": [          {            "id": 2,            "title": "a nibh"          },          {            "id": 9,            "title": "sit amet"          }        ]      }    ]  }}

fetch a list of articles with their author:

 
query {
  article {
    id
    title
    author {
      id
      name
    }
  }
}

Variables

​

xxxxxxxxxx
 
{  "data": {    "article": [      {        "id": 1,        "title": "sit amet",        "author": {          "id": 4,          "name": "Anjela"        }      },      {        "id": 2,        "title": "a nibh",        "author": {          "id": 2,          "name": "Beltran"        }      }    ]  }}

« previous | next »

Was this page helpful?

Want to contribute or report missing content?

edit this page on github | contributing guidelines | report an issue

Hasura GraphQL engine is open source. See license