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Postgres: Tables Basics

Introduction

Adding tables allows you to define the GraphQL types of your schema including their corresponding fields.

Creating tables {#pg-create-tables}

Let's say we want to create two simple tables for articles and author schema:

author (
  id SERIAL PRIMARY KEY,
  name TEXT
)

articles (
  id SERIAL PRIMARY KEY,
  title TEXT,
  content TEXT,
  rating INT,
  author_id INT
)

Open the Hasura Console and head to the Data tab and click on the button on the left side bar to open up an interface to create tables.

For example, here is the schema for the articles table in this interface:

1. Create a migration manually and add the following SQL statement to the up.sql file:

   sqlCopy

   CREATE TABLE articles(id serial NOT NULL, title text NOT NULL, content text NOT NULL, rating integer NOT NULL, author_id serial NOT NULL, PRIMARY KEY (id));
   

2. Add the following statement to the down.sql file in case you need to roll back` the above statement:

   sqlCopy

   DROP TABLE articles;
   

3. Apply the migration by running:

   bashCopy

   hasura migrate apply
   

You can create a table by making an API call to the run_sql schema API:

POST /v2/query HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
  "type": "run_sql",
  "args": {
    "source": "<db_name>",
    "sql": "CREATE TABLE articles(id serial NOT NULL, title text NOT NULL, content text NOT NULL, rating integer NOT NULL, author_id serial NOT NULL, PRIMARY KEY (id));"
  }
}

Tracking tables

Tables can be present in the underlying Postgres database without being exposed over the GraphQL API. In order to expose a table over the GraphQL API, it needs to be tracked.

When a table is created via the Hasura Console, it gets tracked by default.

You can track any existing tables in your database from the Data -> Schema page:

1. To track the table and expose it over the GraphQL API, edit the tables.yaml file in the metadata directory as follows:

   yamlCopy

   - table:
       schema: public
       name: authors
   - table:
       schema: public
       name: articles
   

2. Apply the metadata by running:

   bashCopy

   hasura metadata apply
   

To track the table and expose it over the GraphQL API, make the following API call to the pg_track_table metadata API:

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
  "type": "pg_track_table",
  "args": {
    "source": "<db_name>",
    "schema": "public",
    "name": "articles"
  }
}

Generated GraphQL schema types

As soon as a table is created and tracked, the corresponding GraphQL schema types and query/mutation fields will be automatically generated.

The following object type is generated for the articles table we just created and tracked:

# Object type
type Articles {
  id: Int
  title: String
  content: String
  rating: Int
  author_id: Int
}

Let's analyze the above type:

• Articles is the name of the type
• id, title, content, rating and author_id are fields of the Articles type
• Int and String are types that fields can have

The following query/mutation fields are generated for the articles table we just created and tracked:

# Query field
articles (
  where: articles_bool_exp
  limit: Int
  offset: Int
  order_by: [articles_order_by!]
): [articles!]!

# insert/upsert mutation field
insert_articles (
  objects: [articles_insert_input!]!
  on_conflict: articles_on_conflict
): articles_mutation_response

# update mutation field
update_articles (
  where: articles_bool_exp!
  _inc: articles_inc_input
  _set: articles_set_input
): articles_mutation_response

# delete mutation field
delete_articles (
  where: articles_bool_exp!
): articles_mutation_response

These auto-generated fields will allow you to query and mutate data in our table.

See the query and mutation API references for the full specifications.

GraphQL types documentation

Hasura automatically picks up any comments that might have been added to your tables and columns and adds them as GraphQL descriptions of the auto-generated types and fields.

Try out basic GraphQL requests

At this point, you should be able to try out basic GraphQL queries/mutations on the newly created tables from the API tab in the Console. (You may want to add some sample data into the tables first)

• Query all rows in the articles table:

  <GraphiQLIDE query={query { articles { id title author_id } }} response={{ "data": { "articles": [ { "id": 1, "title": "sit amet", "author_id": 4 }, { "id": 2, "title": "a nibh", "author_id": 2 }, { "id": 3, "title": "amet justo morbi", "author_id": 4 }, { "id": 4, "title": "vestibulum ac est", "author_id": 5 } ] } }} />

• Insert data in the author table:

  <GraphiQLIDE query={mutation add_author { insert_author( objects: [ { name: "Jane" } ] ) { affected_rows returning { id name } } }} response={{ "data": { "insert_author": { "affected_rows": 1, "returning": [ { "id": 11, "name": "Jane" } ] } } }} />

:::info Note

author's id does not need to be passed as an input as it is of type serial (auto incrementing integer).

:::