honeysql/doc/getting-started.md

Getting Started with HoneySQL

HoneySQL lets you build complex SQL statements by constructing and composing Clojure data structures and then formatting that data to a SQL statement (string) and any parameters it needs.

Installation

For the Clojure CLI, add the following dependency to your deps.edn file:

    seancorfield/honeysql {:mvn/version "2.0.0-alpha1"}

For Leiningen, add the following dependency to your project.clj file:

    [seancorfield/honeysql "2.0.0-alpha1"]

Note: 2.0.0-alpha1 will be released shortly!

HoneySQL produces SQL statements but does not execute them. To execute SQL statements, you will also need a JDBC wrapper like seancorfield/next.jdbc and a JDBC driver for the database you use.

Basic Concepts

SQL statements are represented as hash maps, with keys that represent clauses in SQL. SQL expressions are generally represented as vectors, where the first element identifies the function or operator and the remaining elements are the arguments or operands.

honey.sql/format takes a hash map representing a SQL statement and produces a vector, suitable for use with next.jdbc or clojure.java.jdbc, that has the generated SQL string as the first element followed by any parameter values identified in the SQL expressions:

(ns my.example
  (:require [honey.sql :as sql]))

(sql/format {:select [:*], :from [:table], :where [:= :id 1]})
;; produces:
;;=> ["SELECT * FROM table WHERE id = ?" 1]

By default, any values found in the data structure, that are not keywords or symbols, are treated as positional parameters and replaced by ? in the SQL string and lifted out into the vector that is returned from format.

Most clauses expect a vector as their value, containing either a list of SQL entities or the representation of a SQL expression. Some clauses accept a single SQL entity. A few accept a most specialized form (such as :set accepting a hash map of SQL entities and SQL expressions).

A SQL entity can be a simple keyword (or symbol) or a pair that represents a SQL entity and its alias (where aliases are allowed):

(sql/format {:select [:t.id [:name :item]], :from [[:table :t]], :where [:= :id 1]})
;; produces:
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

The FROM clause now has a pair that identifies the SQL entity table and its alias t. Columns can be identified either by their qualified name (as in :t.id) or their unqualified name (as in :name). The SELECT clause here identifies two SQL entities: t.id and name with the latter aliased to item.

Symbols can also be used, but you need to quote them to avoid evaluation:

(sql/format '{select [t.id [name item]], from [[table t]], where [= id 1]})
;; or you can use (..) instead of [..] when quoted:
(sql/format '{select (t.id (name item)), from ((table t)), where (= id 1)})
;; also produces:
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

If you wish, you can specify SQL entities as namespace-qualified keywords (or symbols) and the namespace portion will treated as the table name, i.e., :foo/bar instead of :foo.bar:

(sql/format {:select [:t/id [:name :item]], :from [[:table :t]], :where [:= :id 1]})
;; and
(sql/format '{select [t/id [name item]], from [[table t]], where [= id 1]})
;; both produce:
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

In addition to the hash map (and vectors) approach of building SQL queries with raw Clojure data structures, a namespace full of helper functions is also available. These functions are generally variadic and threadable:

(ns my.example
  (:require [honey.sql :as sql]
            [honey.sql.helpers :refer [select from where]]))

(-> (select :t/id [:name :item])
    (from [:table :t])
    (where [:= :id 1])
    (sql/format))
;; produces:
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

There is a helper function for every single clause that HoneySQL supports out of the box. In addition, there are helpers for composite and over that make it easier to construct those parts of the SQL DSL (examples of the former appear in the README.md, examples of the latter appear in the [docs/clause-reference.md](Clause Reference))

In addition to being variadic -- which often lets you omit one level of [..] -- the helper functions merge clauses, which can make it easier to build queries programmatically:

(-> (select :t/id)
    (from [:table :t])
    (where [:= :id 1])
    (select [:name :item])
    (sql/format))
;; produces:
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

If you want to replace a clause with a subsequent helper call, you need to explicitly remove the prior value:

(-> (select :t/id)
    (from [:table :t])
    (where [:= :id 1])
    (dissoc :select)
    (select [:name :item])
    (sql/format))
;; produces:
;;=> ["SELECT name AS item FROM table AS t WHERE id = ?" 1]

Helpers always use keywords when constructing clauses so you can rely on using keywords in dissoc.

The following helpers shadow functions in clojure.core so you need to consider this when referring symbols in from the honey.sql.helpers namespace: for, group-by, partition-by, set, and update.

Reference Documentation

The full list of supported SQL clauses is documented in the [docs/clause-reference.md](Clause Reference). The full list of "special syntax" functions is documented in the [docs/special-syntax.md](Special Syntax) section. The best documentation for the helper functions is the honey.sql.helpers. If you're migrating to HoneySQL 2.0, this overview of differences between 1.0 and 2.0 should help.