GraphQL

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:

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

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(
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  id serial primary key,
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  email varchar(255) not null
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);
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create function "addAccount"(email text)
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  returns int
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  volatile
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  language sql
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as $$ insert into account (email) values (email) returning id; $$;

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:

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create table account(
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  id serial primary key,
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  email varchar(255) not null
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);
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insert into account(email)
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values
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  ('a@example.com'),
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  ('b@example.com');
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create function "accountById"("accountId" int)
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  returns account
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  stable
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  language sql
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as $$ select id, email from account where id = "accountId"; $$;

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:

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create table account(
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    id int,
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    email varchar(255),
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    name text null
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);
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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);
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create function "returnsAccountWithAllNullColumns"()
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    returns account language sql stable
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as $$ select id, email, name from account where id is null; $$;

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

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create table "Account"(
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  id serial primary key,
3
  email varchar(255) not null
4
);
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insert into "Account"(email)
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values
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  ('a@example.com'),
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  ('a@example.com'),
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  ('b@example.com');
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create function "accountsByEmail"("emailToSearch" text)
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  returns setof "Account"
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  stable
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  language sql
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as $$ select id, email from "Account" where email = "emailToSearch"; $$;

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:

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create table "Account"(
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  id serial primary key,
3
  email varchar(255) not null
4
);
5
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insert into "Account"(email)
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values
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  ('a@example.com'),
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  ('b@example.com'),
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  ('c@example.com');
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create function "accountsByIds"("ids" int[])
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  returns setof "Account"
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  stable
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  language sql
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as $$ select id, email from "Account" where id = any(ids); $$;

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)
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  returns int
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  immutable
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  language sql
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as $$ select a + b; $$;

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

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create function "addNums"(a int default null, b int default null)
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    returns int
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    immutable
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    language plpgsql
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as $$
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begin
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    if a is null and b is null then
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        raise exception 'a and b both can''t be null';
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    end if;
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    if a is null then
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        return b;
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    end if;
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    if b is null then
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        return a;
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    end if;
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    return a + b;
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end;
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$$;

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