Functions

Using Postgres Functions with GraphQL.

Functions can be exposed by pg_graphql to allow running custom queries or mutations.

Query vs Mutation

For example, a function to add two numbers will be available on the query type as a field:

1
create function "addNums"(a int, b int)
2
  returns int
3
  immutable
4
  language sql
5
as $$ select a + b; $$;

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type Query {
2
  addNums(a: Int!, b: Int!): Int
3
}

1
query {
2
  addNums(a: 2, b: 3)
3
}

1
{
2
  "data": {
3
    "addNums": 5
4
  }
5
}

Functions marked immutable or stable are available on the query type. Functions marked with the default volatile category are available on the mutation type:

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create table account(
2
  id serial primary key,
3
  email varchar(255) not null
4
);
5
6
create function "addAccount"(email text)
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  returns int
8
  volatile
9
  language sql
10
as $$ insert into account (email) values (email) returning id; $$;

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type Mutation {
2
  addAccount(email: String!): Int
3
}

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mutation {
2
  addAccount(email: "email@example.com")
3
}

1
{
2
  "data": {
3
    "addAccount": 1
4
  }
5
}

Supported Return Types

Built-in GraphQL scalar types Int, Float, String, Boolean and custom scalar types are supported as function arguments and return types. Function types returning a table or view are supported as well. Such functions implement the Node interface:

1
create table account(
2
  id serial primary key,
3
  email varchar(255) not null
4
);
5
6
insert into account(email)
7
values
8
  ('a@example.com'),
9
  ('b@example.com');
10
11
create function "accountById"("accountId" int)
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  returns account
13
  stable
14
  language sql
15
as $$ select id, email from account where id = "accountId"; $$;

1
type Query {
2
  accountById(email: String!): Account
3
}

1
query {
2
  accountById(accountId: 1) {
3
      id
4
      email
5
      nodeId
6
  }
7
}

1
{
2
  "data": {
3
    "accountById": {
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      "id": 1,
5
      "email": "a@example.com"
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      "nodeId": "WyJwdWJsaWMiLCAiYWNjb3VudCIsIDFd"
7
    }
8
  }
9
}

Since Postgres considers a row/composite type containing only null values to be null, the result can be a little surprising in this case. Instead of an object with all columns null, the top-level field is null:

1
create table account(
2
    id int,
3
    email varchar(255),
4
    name text null
5
);
6
7
insert into account(id, email, name)
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values
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    (1, 'aardvark@x.com', 'aardvark'),
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    (2, 'bat@x.com', null),
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    (null, null, null);
12
13
create function "returnsAccountWithAllNullColumns"()
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    returns account language sql stable
15
as $$ select id, email, name from account where id is null; $$;

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query {
2
  returnsAccountWithAllNullColumns {
3
    id
4
    email
5
    name
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    __typename
7
  }
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}

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{
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  "data": {
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    "returnsAccountWithAllNullColumns": null
4
  }
5
}

Functions returning multiple rows of a table or view are exposed as collections.

1
create table "Account"(
2
  id serial primary key,
3
  email varchar(255) not null
4
);
5
6
insert into "Account"(email)
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values
8
  ('a@example.com'),
9
  ('a@example.com'),
10
  ('b@example.com');
11
12
create function "accountsByEmail"("emailToSearch" text)
13
  returns setof "Account"
14
  stable
15
  language sql
16
as $$ select id, email from "Account" where email = "emailToSearch"; $$;

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type Query {
2
  accountsByEmail(
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    emailToSearch: String!
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    """Query the first `n` records in the collection"""
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    first: Int
7
8
    """Query the last `n` records in the collection"""
9
    last: Int
10
11
    """Query values in the collection before the provided cursor"""
12
    before: Cursor
13
14
    """Query values in the collection after the provided cursor"""
15
    after: Cursor
16
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    """Filters to apply to the results set when querying from the collection"""
18
    filter: AccountFilter
19
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    """Sort order to apply to the collection"""
21
    orderBy: [AccountOrderBy!]
22
  ): AccountConnection
23
}

1
query {
2
  accountsByEmail(emailToSearch: "a@example.com", first: 1) {
3
    edges {
4
      node {
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        id
6
        email
7
      }
8
    }
9
  }
10
}

1
{
2
  "data": {
3
    "accountsByEmail": {
4
      "edges": [
5
        {
6
          "node": {
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            "id": 1,
8
            "email": "a@example.com"
9
          }
10
        }
11
      ]
12
    }
13
  }
14
}

A set returning function with any of its argument names clashing with argument names of a collection (first, last, before, after, filter, or orderBy) will not be exposed.

Functions accepting or returning arrays of non-composite types are also supported. In the following example, the ids array is used to filter rows from the Account table:

1
create table "Account"(
2
  id serial primary key,
3
  email varchar(255) not null
4
);
5
6
insert into "Account"(email)
7
values
8
  ('a@example.com'),
9
  ('b@example.com'),
10
  ('c@example.com');
11
12
create function "accountsByIds"("ids" int[])
13
  returns setof "Account"
14
  stable
15
  language sql
16
as $$ select id, email from "Account" where id = any(ids); $$;

1
type Query {
2
  accountsByIds(
3
    ids: Int[]!
4
5
    """Query the first `n` records in the collection"""
6
    first: Int
7
8
    """Query the last `n` records in the collection"""
9
    last: Int
10
11
    """Query values in the collection before the provided cursor"""
12
    before: Cursor
13
14
    """Query values in the collection after the provided cursor"""
15
    after: Cursor
16
17
    """Filters to apply to the results set when querying from the collection"""
18
    filter: AccountFilter
19
20
    """Sort order to apply to the collection"""
21
    orderBy: [AccountOrderBy!]
22
  ): AccountConnection
23
}

1
query {
2
  accountsByIds(ids: [1, 2]) {
3
    edges {
4
      node {
5
        id
6
        email
7
      }
8
    }
9
  }
10
}

1
{
2
  "data": {
3
    "accountsByIds": {
4
      "edges": [
5
        {
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          "node": {
7
            "id": 1,
8
            "email": "a@example.com"
9
          }
10
        },
11
        {
12
          "node": {
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            "id": 2,
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            "email": "b@example.com"
15
          }
16
        }
17
      ]
18
    }
19
  }
20
}

Default Arguments

Arguments without a default value are required in the GraphQL schema, to make them optional they should have a default value.

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create function "addNums"(a int default 1, b int default 2)
2
  returns int
3
  immutable
4
  language sql
5
as $$ select a + b; $$;

1
type Query {
2
  addNums(a: Int, b: Int): Int
3
}

1
query {
2
  addNums(b: 20)
3
}

1
{
2
  "data": {
3
    "addNums": 21
4
  }
5
}

If there is no sensible default, and you still want to make the argument optional, consider using the default value null.

1
create function "addNums"(a int default null, b int default null)
2
    returns int
3
    immutable
4
    language plpgsql
5
as $$
6
begin
7
8
    if a is null and b is null then
9
        raise exception 'a and b both can''t be null';
10
    end if;
11
12
    if a is null then
13
        return b;
14
    end if;
15
16
    if b is null then
17
        return a;
18
    end if;
19
20
    return a + b;
21
end;
22
$$;

1
type Query {
2
  addNums(a: Int, b: Int): Int
3
}

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query {
2
  addNums(a: 42)
3
}

1
{
2
  "data": {
3
    "addNums": 42
4
  }
5
}

Currently, null defaults are only supported as simple expressions, as shown in the previous example.

Limitations

The following features are not yet supported. Any function using these features is not exposed in the API:

Functions that accept a table's tuple type
Overloaded functions
Functions with a nameless argument
Functions returning void
Variadic functions
Functions that accept or return an array of composite type
Functions that accept or return an enum type or an array of enum type

Functions

Query vs Mutation

Supported Return Types

Default Arguments

Limitations

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