The latest 0.1.11 release of PG2 introduces HugSQL support.

The pg2-hugsql package brings integration with the HugSQL library. It creates functions out from SQL files like HugSQL does but these functions use the PG2 client instead of JDBC. Under the hood, there is a special database adapter as well as a slight override of protocols to make inner HugSQL stuff compatible with PG2.

Since the package already depends on core HugSQL functionality, there is no need to add the latter to dependencies: having pg2-hugsql by itself will be enough (see Installation).

Basic Usage

Let’s go through a short demo. Imagine we have a demo.sql file with the following queries:

-- :name create-demo-table :!
create table :i:table (id serial primary key, title text not null);

-- :name insert-into-table :! :n
insert into :i:table (title) values (:title);

-- :name insert-into-table-returning :<!
insert into :i:table (title) values (:title) returning *;

-- :name select-from-table :? :*
select * from :i:table order by id;

-- :name get-by-id :? :1
select * from :i:table where id = :id limit 1;

-- :name get-by-ids :? :*
select * from :i:table where id in (:v*:ids) order by id;

-- :name insert-rows :<!
insert into :i:table (id, title) values :t*:rows returning *;

-- :name update-title-by-id :<!
update :i:table set title = :title where id = :id returning *;

-- :name delete-from-tablee :n
delete from :i:table;

Prepare a namespace with all the imports:

(ns pg.demo
  (:require
   [clojure.java.io :as io]
   [pg.hugsql :as hug]
   [pg.core :as pg]))

To inject functions from the file, pass it into the pg.hugsql/def-db-fns function:

(hug/def-db-fns (io/file "test/demo.sql"))

It accepts either a string path to a file, a resource, or a File object. Should there were no exceptions, and the file was correct, the current namespace will get new functions declared in the file. Let’s examine them and their metadata:

create-demo-table
#function[pg.demo...]

(-> create-demo-table var meta)

{:doc ""
 :command :!
 :result :raw
 :file "test/demo.sql"
 :line 2
 :arglists ([db] [db params] [db params opt])
 :name create-demo-table
 :ns #namespace[pg.demo]}

Each newborn function has at most three bodies:

  • [db]
  • [db params]
  • [db params opt],

where:

  • db is a source of a connection. It might either a Connection object, a plain Clojure config map, or a Pool object.
  • params is a map of HugSQL parameters like {:id 42};
  • opt is a map of pg/execute parameters that affect processing the current query.

Now that we have functions, let’s call them. Establish a connection first:

(def config
  {:host "127.0.0.1"
   :port 10140
   :user "test"
   :password "test"
   :dbname "test"})

(def conn
  (jdbc/get-connection config))

Let’s create a table using the create-demo-table function:

(def TABLE "demo123")

(create-demo-table conn {:table TABLE})
{:command "CREATE TABLE"}

Insert something into the table:

(insert-into-table conn {:table TABLE
                         :title "hello"})
1

The insert-into-table function has the :n flag in the source SQL file. Thus, it returns the number of rows affected by the command. Above, there was a single record inserted.

Let’s try an expression that inserts something and returns the data:

(insert-into-table-returning conn
                             {:table TABLE
                              :title "test"})
[{:title "test", :id 2}]

Now that the table is not empty any longer, let’s select from it:

(select-from-table conn {:table TABLE})

[{:title "hello", :id 1}
 {:title "test", :id 2}]

The get-by-id shortcut fetches a single row by its primary key. It returs nil for a missing key:

(get-by-id conn {:table TABLE
                 :id 1})
{:title "hello", :id 1}

(get-by-id conn {:table TABLE
                 :id 123})
nil

Its bulk version called get-by-ids relies on the in (:v*:ids) HugSQL syntax. It expands into the following SQL vector: ["... where id in ($1, $2, ... )" 1 2 ...]

-- :name get-by-ids :? :*
select * from :i:table where id in (:v*:ids) order by id;

(get-by-ids conn {:table TABLE
                  :ids [1 2 3]})

;; 3 is missing
[{:title "hello", :id 1}
 {:title "test", :id 2}]

To insert multiple rows at once, use the :t* syntax which is short for “tuple list”. Such a parameter expects a sequence of sequences:

-- :name insert-rows :<!
insert into :i:table (id, title) values :t*:rows returning *;

(insert-rows conn {:table TABLE
                   :rows [[10 "test10"]
                          [11 "test11"]
                          [12 "test12"]]})

[{:title "test10", :id 10}
 {:title "test11", :id 11}
 {:title "test12", :id 12}]

Let’s update a single row by its id:

(update-title-by-id conn {:table TABLE
                          :id 1
                          :title "NEW TITLE"})
[{:title "NEW TITLE", :id 1}]

Finally, clean up the table:

(delete-from-table conn {:table TABLE})

Passing the Source of a Connection

Above, we’ve been passing a Connection object called conn to all functions. But it can be something else as well: a config map or a pool object. Here is an example with a map:

(insert-rows {:host "..." :port ... :user "..."}
             {:table TABLE
              :rows [[10 "test10"]
                     [11 "test11"]
                     [12 "test12"]]})

Pay attention that, when the first argument is a config map, a Connection object is established from it, and then it gets closed afterward before exiting a function. This might break a pipeline if you rely on a state stored in a connection. A temporary table is a good example. Once you close a connection, all the temporary tables created within this connection get wiped. Thus, if you create a temp table in the first function, and select from it using the second function passing a config map, that won’t work: the second function won’t know anything about that table.

The first argument might be a Pool instsance as well:

(pool/with-pool [pool config]
  (let [item1 (get-by-id pool {:table TABLE :id 10})
        item2 (get-by-id pool {:table TABLE :id 11})]
    {:item1 item1
     :item2 item2}))

{:item1 {:title "test10", :id 10},
 :item2 {:title "test11", :id 11}}

When the source a pool, each function call borrows a connection from it and returns it back afterwards. But you cannot be sure that both get-by-id calls share the same connection. A parallel thread may interfere and borrow a connection used in the first get-by-id before the second get-by-id call acquires it. As a result, any pipeline that relies on a shared state across two subsequent function calls might break.

To ensure the functions share the same connection, use either pg/with-connection or pool/with-connection macros:

(pool/with-pool [pool config]
  (pool/with-connection [conn pool]
    (pg/with-tx [conn]
      (insert-into-table conn {:table TABLE :title "AAA"})
      (insert-into-table conn {:table TABLE :title "BBB"}))))

Above, there is 100% guarantee that both insert-into-table calls share the same conn object borrowed from the pool. It is also wrapped into transaction which produces the following session:

BEGIN
insert into demo123 (title) values ($1);
  parameters: $1 = 'AAA'
insert into demo123 (title) values ($1);
  parameters: $1 = 'BBB'
COMMIT

Passing Options

PG2 supports a lot of options when processing a query. To use them, pass a map into the third parameter of any function. Above, we override a function that processes column names. Let it be not the default keyword but clojure.string/upper-case:

(get-by-id conn
           {:table TABLE :id 1}
           {:fn-key str/upper-case})

{"TITLE" "AAA", "ID" 1}

If you need such keys everywhere, submitting a map into each call might be inconvenient. The def-db-fns function accepts a map of predefined overrides:

(hug/def-db-fns
  (io/file "test/demo.sql")
  {:fn-key str/upper-case})

Now, all the generated functions return string column names in upper case by default:

(get-by-id config
           {:table TABLE :id 1})

{"TITLE" "AAA", "ID" 1}

For more details, refer to the official HugSQL documentation.