Table of Content

PG2 version 0.1.4 is out. In this release, the main feature is improvements made to the pg-honey package which is a wrapper on top of HoneySQL.

HoneySQL Integration & Shortcuts

The pg-honey package allows you to call query and execute functions using maps rather than string SQL expressions. Internally, maps are transformed into SQL using the great HoneySQL library. With HoneySQL, you don’t need to format strings to build a SQL, which is clumsy and dangerous in terms of injections.

The package also provides several shortcuts for such common dutiles as get a single row by id, get a bunch of rows by their ids, insert a row having a map of values, update by a map and so on.

For a demo, let’s import the package, declare a config map and create a table with some rows as follows:

(require '[pg.honey :as pgh])

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

(def conn
  (pg/connect config))

(pg/query conn "create table test003 (
  id integer not null,
  name text not null,
  active boolean not null default true
)")

(pg/query conn "insert into test003 (id, name, active)
  values
  (1, 'Ivan', true),
  (2, 'Huan', false),
  (3, 'Juan', true)")

Get by id(s)

The get-by-id function fetches a single row by a primary key which is :id by default:

(pgh/get-by-id conn :test003 1)
;; {:name "Ivan", :active true, :id 1}

With options, you can specify the name of the primary key and the column names you’re interested in:

(pgh/get-by-id conn
               :test003
               1
               {:pk [:raw "test003.id"]
                :fields [:id :name]})

;; {:name "Ivan", :id 1}

;; SELECT id, name FROM test003 WHERE test003.id = $1 LIMIT $2
;; parameters: $1 = '1', $2 = '1'

The get-by-ids function accepts a collection of primary keys and fetches them using the IN operator. In additon to options that get-by-id has, you can specify the ordering:

(pgh/get-by-ids conn
                :test003
                [1 3 999]
                {:pk [:raw "test003.id"]
                 :fields [:id :name]
                 :order-by [[:id :desc]]})

[{:name "Juan", :id 3}
 {:name "Ivan", :id 1}]

;; SELECT id, name FROM test003 WHERE test003.id IN ($1, $2, $3) ORDER BY id DESC
;; parameters: $1 = '1', $2 = '3', $3 = '999'

Passing many IDs at once is not recommended. Either pass them by chunks or create a temporary table, COPY IN ids into it and INNER JOIN with the main table.

Delete

The delete function removes rows from a table. By default, all the rows are deleted with no filtering, and the deleted rows are returned:

(pgh/delete conn :test003)

[{:name "Ivan", :active true, :id 1}
 {:name "Huan", :active false, :id 2}
 {:name "Juan", :active true, :id 3}]

You can specify the WHERE clause and the column names of the result:

(pgh/delete conn
            :test003
            {:where [:and
                     [:= :id 3]
                     [:= :active true]]
             :returning [:*]})

[{:name "Juan", :active true, :id 3}]

When the :returning option set to nil, no rows are returned.

Insert (one)

To observe all the features of the insert function, let’s create a separate table:

(pg/query conn "create table test004 (
  id serial primary key,
  name text not null,
  active boolean not null default true
)")

The insert function accepts a collection of maps each represents a row:

(pgh/insert conn
            :test004
            [{:name "Foo" :active false}
             {:name "Bar" :active true}]
            {:returning [:id :name]})

[{:name "Foo", :id 1}
 {:name "Bar", :id 2}]

It also accepts options to produce the ON CONFLICT ... DO ... clause known as UPSERT. The following query tries to insert two rows with existing primary keys. Should they exist, the query updates the names of the corresponding rows:

(pgh/insert conn
            :test004
            [{:id 1 :name "Snip"}
             {:id 2 :name "Snap"}]
            {:on-conflict [:id]
             :do-update-set [:name]
             :returning [:id :name]})

The resulting query looks like this:

INSERT INTO test004 (id, name) VALUES ($1, $2), ($3, $4)
  ON CONFLICT (id)
  DO UPDATE SET name = EXCLUDED.name
  RETURNING id, name
parameters: $1 = '1', $2 = 'Snip', $3 = '2', $4 = 'Snap'

The insert-one function acts like insert but accepts and returns a single map. It supports :returning and ON CONFLICT ... clauses as well:

(pgh/insert-one conn
                :test004
                {:id 2 :name "Alter Ego" :active true}
                {:on-conflict [:id]
                 :do-update-set [:name :active]
                 :returning [:*]})

{:name "Alter Ego", :active true, :id 2}

The logs:

INSERT INTO test004 (id, name, active) VALUES ($1, $2, TRUE)
  ON CONFLICT (id)
  DO UPDATE SET name = EXCLUDED.name, active = EXCLUDED.active
  RETURNING *
parameters: $1 = '2', $2 = 'Alter Ego'

Update

The update function alters rows in a table. By default, it doesn’t do any filtering and returns all the rows affected. The following query sets the boolean active value for all rows:

(pgh/update conn
            :test003
            {:active true})

[{:name "Ivan", :active true, :id 1}
 {:name "Huan", :active true, :id 2}
 {:name "Juan", :active true, :id 3}]

The :where clause determines conditions for update. You can also specify columns to return:

(pgh/update conn
            :test003
            {:active false}
            {:where [:= :name "Ivan"]
             :returning [:id]})

[{:id 1}]

What is great about update is, you can use such complex expressions as increasing counters, negation and so on. Below, we alter the primary key by adding 100 to it, negate the active column, and change the name column with dull concatenation:

(pgh/update conn
            :test003
            {:id [:+ :id 100]
             :active [:not :active]
             :name [:raw "name || name"]}
            {:where [:= :name "Ivan"]
             :returning [:id :active]})

[{:active true, :id 101}]

Which produces the following query:

UPDATE test003
  SET
    id = id + $1,
    active = NOT active,
    name = name || name
  WHERE name = $2
  RETURNING id, active
parameters: $1 = '100', $2 = 'Ivan'

Find (first)

The find function makes a lookup in a table by column-value pairs. All the pairs are joined using the AND operator:

(pgh/find conn :test003 {:active true})

[{:name "Ivan", :active true, :id 1}
 {:name "Juan", :active true, :id 3}]

Find by two conditions:

(pgh/find conn :test003 {:active true
                         :name "Juan"})

[{:name "Juan", :active true, :id 3}]

;; SELECT * FROM test003 WHERE (active = TRUE) AND (name = $1)
;; parameters: $1 = 'Juan'

The function accepts additional options for LIMIT, OFFSET, and ORDER BY clauses:

(pgh/find conn
          :test003
          {:active true}
          {:fields [:id :name]
           :limit 10
           :offset 1
           :order-by [[:id :desc]]
           :fn-key identity})

[{"id" 1, "name" "Ivan"}]

;; SELECT id, name FROM test003
;;   WHERE (active = TRUE)
;;   ORDER BY id DESC
;;   LIMIT $1
;;   OFFSET $2
;; parameters: $1 = '10', $2 = '1'

The find-first function acts the same but returns a single row or nil. Internally, it adds the LIMIT 1 clause to the query:

(pgh/find-first conn :test003
                {:active true}
                {:fields [:id :name]
                 :offset 1
                 :order-by [[:id :desc]]
                 :fn-key identity})

{"id" 1, "name" "Ivan"}

Prepare

The prepare function makes a prepared statement from a HoneySQL map:

(def stmt
  (pgh/prepare conn {:select [:*]
                     :from :test003
                     :where [:= :id 0]}))

;; <Prepared statement, name: s37, param(s): 1, OIDs: [INT8], SQL: SELECT * FROM test003 WHERE id = $1>

Above, the zero value is a placeholder for an integer parameter.

Now that the statement is prepared, execute it with the right id:

(pg/execute-statement conn stmt {:params [3]
                                 :first? true})

{:name "Juan", :active true, :id 3}

Alternately, use the [:raw ...] syntax to specify a parameter with a dollar sign:

(def stmt
  (pgh/prepare conn {:select [:*]
                     :from :test003
                     :where [:raw "id = $1"]}))

(pg/execute-statement conn stmt {:params [1]
                                 :first? true})

{:name "Ivan", :active true, :id 1}

Query and Execute

There are two general functions called query and execute. Each of them accepts an arbitrary HoneySQL map and performs either Query or Execute request to the server.

Pay attention that, when using query, a HoneySQL map cannot have parameters. This is a limitation of the Query command. The following query will lead to an error response from the server:

(pgh/query conn
           {:select [:id]
            :from :test003
            :where [:= :name "Ivan"]
            :order-by [:id]})

;; Execution error (PGErrorResponse) at org.pg.Accum/maybeThrowError (Accum.java:207).
;; Server error response: {severity=ERROR, ... message=there is no parameter $1, verbosity=ERROR}

Instead, use either [:raw ...] syntax or {:inline true} option:

(pgh/query conn
           {:select [:id]
            :from :test003
            :where [:raw "name = 'Ivan'"] ;; raw (as is)
            :order-by [:id]})

[{:id 1}]

;; OR

(pgh/query conn
           {:select [:id]
            :from :test003
            :where [:= :name "Ivan"]
            :order-by [:id]}
           {:honey {:inline true}}) ;; inline values

[{:id 1}]

;; SELECT id FROM test003 WHERE name = 'Ivan' ORDER BY id ASC

The execute function acceps a HoneySQL map with parameters:

(pgh/execute conn
               {:select [:id :name]
                :from :test003
                :where [:= :name "Ivan"]
                :order-by [:id]})

[{:name "Ivan", :id 1}]

Both query and execute accept not SELECT only but literally everything: inserting, updating, creating a table, an index, and more. You can build combinations like INSERT ... FROM SELECT or UPDATE ... FROM DELETE to perform complex logic in a single atomic query.

HoneySQL options

Any HoneySQL-specific parameter might be passed through the :honey submap in options. Below, we pass the :params map to use the [:param ...] syntax. Also, we produce a pretty-formatted SQL for better logs:

(pgh/execute conn
             {:select [:id :name]
              :from :test003
              :where [:= :name [:param :name]]
              :order-by [:id]}
             {:honey {:pretty true
                      :params {:name "Ivan"}}})

;; SELECT id, name
;; FROM test003
;; WHERE name = $1
;; ORDER BY id ASC
;; parameters: $1 = 'Ivan'

For more options, please refer to the official HoneySQL documentation.

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