Functions as RPC

“A single resource can be the equivalent of a database function, with the power to abstract state changes over any number of storage items” – Roy T. Fielding

Functions can perform any operation allowed by PostgreSQL (read data, modify data, raise errors, and even DDL operations). Every function in the exposed schema and accessible by the active database role is executable under the /rpc prefix.

If they return table types, functions can:

Note

Why the /rpc prefix? PostgreSQL allows a table or view to have the same name as a function. The prefix allows us to avoid routes collisions.

Warning

Stored Procedures are not supported.

Calling with POST

To supply arguments in an API call, include a JSON object in the request payload. Each key/value of the object will become an argument.

For instance, assume we have created this function in the database.

CREATE FUNCTION add_them(a integer, b integer)
RETURNS integer AS $$
 SELECT a + b;
$$ LANGUAGE SQL IMMUTABLE;

Important

Whenever you create or change a function you must refresh PostgREST’s schema cache. See the section Schema Cache Reloading.

The client can call it by posting an object like

curl "http://localhost:3000/rpc/add_them" \
  -X POST -H "Content-Type: application/json" \
  -d '{ "a": 1, "b": 2 }'

3

Note

PostgreSQL converts identifier names to lowercase unless you quote them like:

CREATE FUNCTION "someFunc"("someParam" text) ...

Calling with GET

If the function doesn’t modify the database, it will also run under the GET method (see Access Mode).

curl "http://localhost:3000/rpc/add_them?a=1&b=2"

The function parameter names match the JSON object keys in the POST case, for the GET case they match the query parameters ?a=1&b=2.

Functions with a single unnamed JSON parameter

If you want the JSON request body to be sent as a single argument, you can create a function with a single unnamed json or jsonb parameter. For this the Content-Type: application/json header must be included in the request.

CREATE FUNCTION mult_them(json) RETURNS int AS $$
  SELECT ($1->>'x')::int * ($1->>'y')::int
$$ LANGUAGE SQL;

curl "http://localhost:3000/rpc/mult_them" \
  -X POST -H "Content-Type: application/json" \
  -d '{ "x": 4, "y": 2 }'

8

Note

If an overloaded function has a single json or jsonb unnamed parameter, PostgREST will call this function as a fallback provided that no other overloaded function is found with the parameters sent in the POST request.

Warning

Sending the JSON request body as a single argument is also possible with Prefer: params=single-object but this method is deprecated.

Functions with a single unnamed parameter

You can make a POST request to a function with a single unnamed parameter to send raw bytea, text or xml data.

To send raw XML, the parameter type must be xml and the header Content-Type: text/xml must be included in the request.

To send raw binary, the parameter type must be bytea and the header Content-Type: application/octet-stream must be included in the request.

CREATE TABLE files(blob bytea);

CREATE FUNCTION upload_binary(bytea) RETURNS void AS $$
  INSERT INTO files(blob) VALUES ($1);
$$ LANGUAGE SQL;

curl "http://localhost:3000/rpc/upload_binary" \
  -X POST -H "Content-Type: application/octet-stream" \
  --data-binary "@file_name.ext"

HTTP/1.1 200 OK

[ ... ]

To send raw text, the parameter type must be text and the header Content-Type: text/plain must be included in the request.

Functions with array parameters

You can call a function that takes an array parameter:

create function plus_one(arr int[]) returns int[] as $$
   SELECT array_agg(n + 1) FROM unnest($1) AS n;
$$ language sql;

curl "http://localhost:3000/rpc/plus_one" \
  -X POST -H "Content-Type: application/json" \
  -d '{"arr": [1,2,3,4]}'

[2,3,4,5]

For calling the function with GET, you can pass the array as an array literal, as in {1,2,3,4}. Note that the curly brackets have to be urlencoded({ is %7B and } is %7D).

curl "http://localhost:3000/rpc/plus_one?arr=%7B1,2,3,4%7D'"

Note

For versions prior to PostgreSQL 10, to pass a PostgreSQL native array on a POST payload, you need to quote it and use an array literal:

curl "http://localhost:3000/rpc/plus_one" \
  -X POST -H "Content-Type: application/json" \
  -d '{ "arr": "{1,2,3,4}" }'

In these versions we recommend using function parameters of type JSON to accept arrays from the client.

Variadic functions

You can call a variadic function by passing a JSON array in a POST request:

create function plus_one(variadic v int[]) returns int[] as $$
   SELECT array_agg(n + 1) FROM unnest($1) AS n;
$$ language sql;

curl "http://localhost:3000/rpc/plus_one" \
  -X POST -H "Content-Type: application/json" \
  -d '{"v": [1,2,3,4]}'

[2,3,4,5]

In a GET request, you can repeat the same parameter name:

curl "http://localhost:3000/rpc/plus_one?v=1&v=2&v=3&v=4"

Repeating also works in POST requests with Content-Type: application/x-www-form-urlencoded:

curl "http://localhost:3000/rpc/plus_one" \
  -X POST -H "Content-Type: application/x-www-form-urlencoded" \
  -d 'v=1&v=2&v=3&v=4'

Table-Valued Functions

A function that returns a table type can be filtered using the same filters as tables and views. They can also use Resource Embedding.

CREATE FUNCTION best_films_2017() RETURNS SETOF films ..

curl "http://localhost:3000/rpc/best_films_2017?select=title,director:directors(*)"

curl "http://localhost:3000/rpc/best_films_2017?rating=gt.8&order=title.desc"

Function Inlining

A function that follows the rules for inlining will also inline filters, order and limits.

For example, for the following function:

create function getallprojects() returns setof projects
language sql stable
as $$
  select * from projects;
$$;

Let’s get its Execution plan when calling it with filters applied:

curl "http://localhost:3000/rpc/getallprojects?id=eq.1" \
  -H "Accept: application/vnd.pgrst.plan"

Aggregate  (cost=8.18..8.20 rows=1 width=112)
  ->  Index Scan using projects_pkey on projects  (cost=0.15..8.17 rows=1 width=40)
        Index Cond: (id = 1)

Notice there’s no “Function Scan” node in the plan, which tells us it has been inlined.

Scalar functions

PostgREST will detect if the function is scalar or table-valued and will shape the response format accordingly:

curl "http://localhost:3000/rpc/add_them?a=1&b=2"

3

curl "http://localhost:3000/rpc/best_films_2017"

[
  { "title": "Okja", "rating": 7.4},
  { "title": "Call me by your name", "rating": 8},
  { "title": "Blade Runner 2049", "rating": 8.1}
]

To manually choose a return format such as binary, see Media Type Handlers.

Untyped functions

Functions that return record or SETOF record are supported:

create function projects_setof_record() returns setof record as $$
  select * from projects;
$$ language sql;

curl "http://localhost:3000/rpc/projects_setof_record"

[{"id":1,"name":"Windows 7","client_id":1},
 {"id":2,"name":"Windows 10","client_id":1},
 {"id":3,"name":"IOS","client_id":2}]

However note that they will fail when trying to use Vertical Filtering and Horizontal Filtering on them.

So while they can be used for quick tests, it’s recommended to always choose a strict return type for the function.

Overloaded functions

You can call overloaded functions with different number of arguments.

CREATE FUNCTION rental_duration(customer_id integer) ..

CREATE FUNCTION rental_duration(customer_id integer, from_date date) ..

curl "http://localhost:3000/rpc/rental_duration?customer_id=232"

curl "http://localhost:3000/rpc/rental_duration?customer_id=232&from_date=2018-07-01"

Important

Overloaded functions with the same argument names but different types are not supported.