PostgreSQL's Secret NoSQL Superpowers

PostgreSQL’s Secret
NoSQL Superpowers
Amanda Gilmore

Postgres supports several
document data formats.

How do you choose?
Do you wrap a foreign database?

How do you choose?
Do you have a (fairly) standard object schema with weird objects?

How do you choose?
Are you worried about lock contention?

XML
http://www.postgresql.org/docs/9.5/static/functions-xml.html

Schema
CREATE TABLE xml_samples (
id bigserial PRIMARY KEY,
documents xml,
comments text
)

Create
INSERT INTO xml_samples (documents, comments) VALUES (
XMLPARSE( DOCUMENT $$<?xml version="1.0"?>
<catalog>
...
</catalog>$$)
, 'This is an entire XML document')

Create
--Alternatively, this inserts one node per row
INSERT INTO xml_samples (documents, comments) VALUES (
$$<book id="bk101">
<author>Gambardella, Matthew</author>
<title>XML Developer's Guide</title>
<genre>Computer</genre>
<price>44.95</price>
<publish_date>2000-10-01</publish_date>
<description>An in-depth look at creating applications
with XML.</description>
</book>$$
, 'one book per row, as an XML node')

Read
--Gets all titles in the table
SELECT xpath('//book/title', documents) FROM xml_samples
--Gets all info on a book by title
SELECT * FROM xml_samples WHERE (xpath('//book/title/text()'
, documents))[1]::text = 'Midnight Rain'::text

Update
Cannot do this natively.

hstore
http://www.postgresql.org/docs/9.5/static/hstore.html

Schema
CREATE EXTENSION hstore
CREATE TABLE hstore_samples (
documents hstore,
comments text
)

Create
INSERT INTO hstore_samples (documents, comments)
VALUES ('"active_resource"=>"true"
,"resource_name"=>"swimming-swiftly-1234"
,"resource_size_in_mb"=>"30"
,"resource_created_at"=>"2016-03-14 17:20:47.216862"'
, 'this is a straight up K/V hash')

Read
--hstores are strings under the hood and require casting
SELECT * from hstore_samples
WHERE (documents -> 'resource_size_in_mb')::int > 30

Read
--You can get all of the values for a certain key:
SELECT (documents -> 'resource_name')::text
FROM hstore_samples
--or convert the entire table to an hstore:
SELECT hstore(t) FROM hstore_samples AS t

Read
--Pulling multiple values from the document
SELECT (documents -> 'resource_name')::text
, (documents -> 'active_resource')::text
FROM hstore_samples

Update
--Cannot do this in place , hence the || operator
UPDATE hstore_samples
SET documents = documents || '"active_resource"=>"false"'::hstore
WHERE documents @> '"resource_name"=>"swimming-swiftly-1234"'::hstore

json & jsonb
http://www.postgresql.org/docs/9.5/static/datatype-json.html

Read
--get json object. Array element by index (int) or by key
(str)
->
--get json object *by text*
->>
--containment operator, used to get an object by path
@>
--checks for existence of a key
?
http://www.postgresql.org/docs/9.5/static/functions-json.html

Schema
CREATE TABLE json_samples (
text_json json,
binary_json jsonb,
notes text
)

Create
INSERT INTO json_samples (text_json, notes) VALUES (
'{
"minStartTimeNs": "1429828653617000000",
"maxEndTimeNs": "1429839639367000000",
"dataSourceId":
"derived:com.google.heart_rate.bpm:com.google.android.gms:merge_heart_rate_bpm"
}'
, 'This is in the text json field')

Read
--Can check top-level keys before querying:
SELECT jsonb_object_keys(binary_json) FROM json_samples
--Well formed JSON path:
['point'][0]['value'][0]['fpVal']
--And you can extract specific values from the document:
SELECT binary_json->'point'->0->'value'->0->'fpVal' FROM json_samples

--Can check if a given key is present:
SELECT * FROM json_samples WHERE text_json::jsonb ? 'dataSourceId'
SELECT * FROM json_samples WHERE binary_json ? 'dataSourceId'
--And can check if the value of the key matches something:
SELECT * FROM json_samples
WHERE binary_json ->> 'minStartTimeNs' = '1429828653617000000'
Read

Update
--Can update at top level:
UPDATE json_samples
SET binary_json = binary_json || '{"address": {
"streetAddress": "123 Test Street",
"city": "Oakland",
"state": "CA",
"postalCode": "94123"
} }'
WHERE binary_json ->> 'lastName' = 'Gilmore'

Update
--or use jsonb_set() to drill down the tree:
SELECT jsonb_set(binary_json::jsonb
, '{address, streetAddress}'
, '"456 Lorem Ipsum St"'::jsonb)
FROM json_samples
WHERE binary_json ->> 'lastName' = 'Gilmore'

tl;dr
xml Can query on xpath Can’t update
hstore Can index keys Text, less performant
json Richly nested data Text, less performant
jsonb Nested data, fast reads Higher cost writes

xml: http://www.postgresql.org/docs/9.5/static/functions-xml.html
hstore: http://www.postgresql.org/docs/9.5/static/hstore.html
json & jsonb: http://www.postgresql.org/docs/9.5/static/functions-json.html
Source for the xml sample: https://msdn.microsoft.com/en-
us/library/ms762271(v=vs.85).aspx
Sample code for this talk on GitHub:
https://github.com/mandagill/PGConfUS_2016_syntax_samples
Links & References

Thanks, y’all!
amanda@heroku.com
GitHub: mandagill

PostgreSQL's Secret NoSQL Superpowers

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to PostgreSQL's Secret NoSQL Superpowers (20)

Recently uploaded (20)

PostgreSQL's Secret NoSQL Superpowers

Editor's Notes