Requesting Information

Tables and Views

  • ✅ Cacheable, prefetchable
  • ✅ Idempotent

The list of accessible tables and views is provided at

GET /

Every view and table accessible by the active db role is exposed in a one-level deep route. For instance the full contents of a table people is returned at

GET /people

There are no deeply/nested/routes. Each route provides OPTIONS, GET, POST, PATCH, and DELETE verbs depending entirely on database permissions.

Design Consideration

Why not provide nested routes? Many APIs allow nesting to retrieve related information, such as /films/1/director. We offer a more flexible mechanism (inspired by GraphQL) to embed related information. It can handle one-to-many and many-to-many relationships. This is covered in the section about Embedding.

Stored Procedures

  • ❌ Cannot necessarily be cached or prefetched
  • ❌ Not necessarily idempotent

Every stored procedure is accessible under the /rpc prefix. The API endpoint supports only POST which executes the function.

POST /rpc/proc_name

PostgREST supports calling procedures with named arguments. Include a JSON object in the request payload and 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 $$
 SELECT $1 + $2;
$$ LANGUAGE SQL IMMUTABLE STRICT;

The PostgREST client can call it by posting an object like { "a": 1, "b": 2} to /rpc/add_them. The keys of the object match the parameter names. Note that PostgreSQL converts parameter names to lowercase unless you quote them like CREATE FUNCTION foo("mixedCase" text) ....

Design Consideration

Why the /rpc prefix? One reason is to avoid name collisions between views and procedures. It also helps emphasize to API consumers that these functions are not normal restful things. The functions can have arbitrary and surprising behavior, not the standard "post creates a resource" thing that users expect from the other routes.

We considered allowing GET requests for functions that are marked non-volatile but could not reconcile how to pass in parameters. Query string arguments are reserved for shaping/filtering the output, not providing input.

Filtering

Filtering Rows

You can filter result rows by adding conditions on columns, each condition a query string parameter. For instance, to return people aged under 13 years old:

GET /people?age=lt.13

Adding multiple parameters conjoins the conditions:

GET /people?age=gte.18&student=is.true

These operators are available:

abbreviation meaning
eq equals
gte greater than or equal
gt greater than
lte less than or equal
lt less than
neq not equal
like LIKE operator (use * in place of %)
ilike ILIKE operator (use * in place of %)
in one of a list of values e.g. ?a=in.1,2,3
notin not one of a list of values e.g. ?a=notin.1,2,3
is checking for exact equality (null,true,false)
isnot checking for exact inequality (null,true,false)
@@ full-text search using to_tsquery
@> contains e.g. ?tags=@>.{example, new}
<@ contained in e.g. values=<@{1,2,3}
not negates another operator, see below

To negate any operator, prefix it with not like ?a=not.eq.2.

For more complicated filters (such as those involving condition 1 OR condition 2) you will have to create a new view in the database.

Filters may be applied to computed columns as well as actual table/view columns, even though the computed columns will not appear in the output.

Filtering Columns

You can customize which columns are returned by using the select parameter:

GET /people?select=age,height,weight

To cast the column types, add a double colon

GET /people?select=age::text,height,weight

Not all type coercions are possible, and you will get an error describing any problems from selection or type casting.

The select keyword is reserved. You thus cannot filter rows based on a column named select. Then again it is a reserved SQL keyword too, hence an unlikely column name.

Inside JSONB

PostgreSQL >=9.4.2 supports native JSON columns and can even index them by internal keys using the jsonb column type. PostgREST allows you to filter results by internal JSON object values. Use the single- and double-arrows to path into and obtain values, e.g.

GET /stuff?json_col->a->>b=eq.2

This query finds rows in stuff where json_col->'a'->>'b' is equal to 2 (or “2” – it coerces as needed). The final arrow must be the double kind, ->>, or else PostgREST will not attempt to look inside the JSON.

Ordering

The reserved word order reorders the response rows. It uses a comma-separated list of columns and directions:

GET /people?order=age.desc,height.asc

If no direction is specified it defaults to ascending order:

GET /people?order=age

If you care where nulls are sorted, add nullsfirst or nullslast:

GET /people?order=age.nullsfirst
GET /people?order=age.desc.nullslast

You can order by jsonb object values with the same criteria:

GET /people?order=json_col->a->>b.desc.nullslast

To order the embedded items, you need to specify the tree path for the order param like so.

GET /projects?select=id,name,tasks{id,name}&order=id.asc&tasks.order=name.asc

You can also use computed columns to order the results, even though the computed columns will not appear in the output.

Limiting and Pagination

Pagination by Limit-Offset

PostgREST uses HTTP range headers for limiting and describing the size of results. Every response contains the current range and total results:

Range-Unit: items
Content-Range → 0-14/15

This means items zero through fourteen are returned out of a total of fifteen – i.e. all of them. This information is available in every response and can help you render pagination controls on the client. This is a RFC7233-compliant solution that keeps the response JSON cleaner.

The client can set the limit and offset of a request by setting the Range header. Translate the limit and offset into a range. To request the first five elements, include these request headers:

Range-Unit: items
Range: 0-4

You can also use open-ended ranges for an offset with no limit: Range: 10-.

In addition to the Range header, you can use &limit and &offset parameters to achieve the same result.

You can also set a limit (but not offset) for the embedded items like so

/posts?select=id,title,body,comments{id,email,body}&limit=10&comments.limit=3

The above request will return the first 10 posts and for each of the posts, 3 comments at most

Suppressing Counts

Sometimes knowing the total row count of a query is unnecessary and only adds extra cost to the database query. So you can skip the count total using a Prefer header as:

Prefer: count=none

With count suppressed the PostgREST response will look like:

Range-Unit: items
Content-Range → 0-14/*

Embedding Foreign Entities

To help you make fewer requests, PostgREST allows the embedding of traditional SQL relationships into a response. Suppose you have a projects table which references clients through a foreign key called client_id. When listing projects through the API you can have it embed the client within each project response. For example,

GET /projects?id=eq.1&select=id, name, clients{*}

Notice this is the same select keyword which is used to choose which columns to include. When a column name is followed by parentheses that means to fetch the entire record and nest it. You include a list of columns inside the parens, or asterisk to request all columns.

The embedding works for 1-N, N-1, and N-N relationships. That means you could also ask for a client and all their projects:

GET /clients?id=eq.42&select=id, name, projects{*}

In the examples above we asked for all columns in the embedded resource but the the select query is recursive. You could for instance specify

GET /foo?select=x, y, bar{z, w, baz{*}}

You can select not only using table names, but also foreign key column names! This is especially needed when you have a table with two foreign keys pointing to the same table, for example billing_address_id and shipping_address_id. To embed the same foreign key row from our client example earlier you could do the following:

GET /projects?id=eq.1&select=id, name, client_id{*}

In the response there will be a client_id object containing all the data for that row.

However, a client_id object doesn’t make a lot of sense, so you could do one of two things. Tell PostgREST that you want the key renamed by using the alias feature like so client:client_id{*}, or just try client{*} in the select parameter! PostgREST supports smart ducktype checking for common foreign key names, so if your column name ends with _id, _fk, or any variation of the two (including camelcase) you can embed a row with just the name’s beginning.

So for a complete example:

GET /projects?id=eq.1&select=id, name, client{*}

Would embed in the client key the row referenced with client_id.

The alias feature works for embedded entities and also for regular columns. This is useful in situations where for example you use different naming conventions in the database and front-end.

The following request will produce the output below:

GET /orders?id=eq.1&select=orderId:id, customer:customer_id{customerId:id, customerName:name}
[
  {
    "orderId": 1,
    "customer": {
      "customerId": 1,
      "customerName": "John Smith"
    }
  }
]

If you want to apply filters to the embedded items, you can do that like so:

GET /clients?id=eq.42&select=id,name,projects{id,name,is_active}&projects.is_active=eq.true

The above request will return the client with id=42 and all the projects for that client that are still active

Design Consideration

In order for this feature to work as expected after a schema change, PostgREST currently requires to be restarted.

Response Format

Query responses default to JSON but you can get them in CSV as well. Just make your request with the header

Accept: text/csv

Singular vs Plural

Many APIs distinguish plural and singular resources, e.g./stories vs /stories/1. Why do we use /stories?id=eq.1? It is because a single resource is for us a row determined by a primary key, and primary keys can be compound (meaning defined across more than one column). The common urls come from a degenerate case of simple (and overwhelmingly numeric) primary keys often introduced automatically be Object Relational Mapping.

For consistency’s sake all these endpoints return a JSON array, /stories, /stories?genre=eq.mystery, /stories?id=eq.1. They are all filtering a bigger array. However you might want the last one to return a single JSON object, not an array with one element. To request a singular response send the header Prefer: plurality=singular.

Data Schema

As well as issuing a GET / to obtain a list of the tables, views, and stored procedures available, you can get more information about any particular endpoint.

OPTIONS /my_view

This will include the row names, their types, primary key information, and foreign keys for the given table or view.

Schema Changes

Note that when the schema of your database changes PostgREST will not reflect the change. You have to either restart PostgREST or send its running process a HUP signal:

killall -HUP postgrest

CORS

PostgREST sets highly permissive cross origin resource sharing. It accepts Ajax requests from any domain.