EmacSQL is a high-level Emacs Lisp front-end for SQLite (primarily), PostgreSQL, MySQL, and potentially other SQL databases.
It works by maintaining a inferior process running (a "connection") for interacting with the back-end database. Connections are automatically cleaned up if they are garbage collected. All requests are synchronous.
Any readable lisp value can be stored as a value in
EmacSQL, including numbers, strings, symbols, lists, vectors, and
closures. EmacSQL has no concept of "TEXT" values; it's all just lisp
objects. The lisp object
nil corresponds 1:1 with
NULL in the
On MELPA, each backend is provided as a separate package, suffixed
with the database name. In the case of
emacsql-sqlite, on first use
EmacSQL will attempt to compile a custom native binary for
communicating with a SQLite database. If this fails (a C compiler is
not available), it will attempt to download, with permission, a
pre-built binary when the first database connection is attempted. The
official sqlite3 command shell is incapable of correct interaction
when linked with GNU Readline, or when run in Windows, so a custom
build tool is required. If your own package depends on EmacSQL as a
database, this means it doesn't have to rely on the user having any
particular software installed.
Requires Emacs 24.3 or later.
start-process-shell-command function is not supported on
Windows. Since both
emacsql-psql rely on this
function, neither of these connection types are supported on Windows.
(defvar db (emacsql-sqlite "~/company.db")) ;; Create a table. Table and column identifiers are symbols. (emacsql db [:create-table people ([name id salary])]) ;; Or optionally provide column constraints. (emacsql db [:create-table people ([name (id integer :primary-key) (salary float)])]) ;; Insert some data: (emacsql db [:insert :into people :values (["Jeff" 1000 60000.0] ["Susan" 1001 64000.0])]) ;; Query the database for results: (emacsql db [:select [name id] :from people :where (> salary 62000)]) ;; => (("Susan" 1001)) ;; Queries can be templates, using $1, $2, etc.: (emacsql db [:select [name id] :from people :where (> salary $s1)] 50000) ;; => (("Jeff" 1000) ("Susan" 1001))
When editing these prepared SQL s-expression statements, the
emacsql-show-last-sql command (think
eval-last-sexp) is useful for
seeing what the actual SQL expression will become when compiled.
A table schema is a list whose first element is a vector of column
specifications. The rest of the list specifies table constraints. A
column identifier is a symbol and a column's specification can either
be just this symbol or it can include constraints as a list. Because
EmacSQL stores entire lisp objects as values, the only relevant (and
allowed) types are
([(<column>) ...] (<table-constraint> ...) ...])
Dashes in identifiers are converted into underscores when compiled into SQL. This allows for lisp-style identifiers to be used in SQL. Constraints follow the compilation rules below.
;; No constraints schema with four columns: ([name id building room]) ;; Add some column constraints: ([(name :unique) (id integer :primary-key) building room]) ;; Add some table constraints: ([(name :unique) (id integer :primary-key) building room] (:unique [building room]) (:check (> id 0)))
Here's an example using foreign keys.
;; "subjects" table schema ([(id integer :primary-key) subject]) ;; "tag" table references subjects ([(subject-id integer) tag] (:foreign-key [subject-id] :references subjects [id] :on-delete :cascade))
Foreign key constraints are enabled by default in EmacSQL.
Expressions are written lisp-style, with the operator first. If it looks like an operator EmacSQL treats it like an operator. However, several operators are special.
<= >= funcall quote
>= operators accept 2 or 3 operands, transforming into
_ BETWEEN _ AND _ operator as appropriate.
For function-like "operators" like
max use the
[:select (funcall max age) :from people]
Inside expressions, EmacSQL cannot tell the difference between symbol
literals and column references. If you're talking about the symbol
itself, just quote it as you would in normal Elisp. Note that this
does not "escape"
$tn parameter symbols.
(emacsql db [... :where (= category 'hiking)])
Since template parameters include their type they never need to be quoted.
like SQL operators keep in mind that they're
matching the printed representations of these values, even if the
value is a string.
|| concatenation operator is unsupported because concatenating
printed representations breaks an important constraint: all values must
remain readable within SQLite.
The database is interacted with via prepared SQL s-expression statements. You shouldn't normally be concatenating strings on your own. (And it leaves out any possibility of a SQL injection!) See the "Usage" section above for examples. A statement is a vector of keywords and other lisp object.
Prepared EmacSQL s-expression statements are compiled into SQL
statements. The statement compiler is memoized so that using the same
statement multiple times is fast. To assist in this, the statement can
act as a template -- using
$s2, etc. -- working like the
Rather than the typical uppercase SQL keywords, keywords in a prepared EmacSQL statement are literally just that: lisp keywords. EmacSQL only understands a very small amount of SQL's syntax. The compiler follows some simple rules to convert an s-expression into SQL.
All prepared statements are vectors.
A prepared s-expression statement is a vector beginning with a keyword followed by a series of keywords and special values. This includes most kinds of sub-queries.
[:select ... :from ...] [:select tag :from tags :where (in tag [:select ...])]
Keywords are split and capitalized.
Dashes are converted into spaces and the keyword gets capitalized. For
IF NOT EXISTS. How you choose to
combine keywords is up to your personal taste (e.g.
:drop :table vs.
Standalone symbols are identifiers.
EmacSQL doesn't know what symbols refer to identifiers and what
symbols should be treated as values. Use quotes to mark a symbol as a
value. For example,
people here will be treated as an identifier.
[:insert-into people :values ...]
Row-oriented information is always represented as vectors.
This includes rows being inserted, and sets of columns in a query. If you're talking about a row-like thing then put it in a vector.
[:select [id name] :from people]
* is actually a SQL keyword, so don't put it in a vector.
[:select * :from ...]
Lists are treated as expressions.
This is true even within row-oriented vectors.
[... :where (= name "Bob")] [:select [(/ seconds 60) count] :from ...]
Some things that are traditionally keywords -- particularly those that
are mixed in with expressions -- have been converted into operators
[... :order-by [(asc b), (desc a)]] ; "ORDER BY b ASC, a DESC" [:select p:name :from (as people p)] ; "SELECT p.name FROM people AS p"
:values keyword is special.
:values is always treated like a vector or list of
vectors. Normally this sort of thing would appear to be a column
[... :values [1 2 3]] [... :values ([1 2 3] [4 5 6])] ; insert multiple rows
A list whose first element is a vector is a table schema.
This is to distinguish schemas from everything else. With the
exception of what follows
:values, nothing else is shaped like this.
[:create-table people ([(id :primary-key) name])]
To make statement compilation faster, and to avoid making you build up
statements dynamically, you can insert
$tn parameters in place of
identifiers and values. These refer to the argument's type and its
argument position after the statement in the
(emacsql db [:select * :from $i1 :where (> salary $s2)] 'employees 50000)
The letter before the number is the type.
v: vector (or multiple vectors)
When combined with
:values, the vector type can refer to lists of
(emacsql db [:insert-into favorite-characters :values $v1] '([0 "Calvin"] [1 "Hobbes"] [3 "Susie"]))
This is why rows must be vectors and not lists.
The custom EmacSQL SQLite binary is compiled with Soundex
and full-text search (FTS4) enabled -- features disabled by the
default SQLite build. This backend should work on any system with a
compliant C compiler installed as
cc. If you don't have a C compiler
installed the following platforms will be able to fetch a pre-built
- Linux x86 and x86_64
- OS X x86_64
- Windows x86 and x86_64, including Cygwin
- Linux armv6l (Raspberry Pi + Raspbian)
The customization variable
the behavior of SQLite binary fetching, and the variable
emacsql-sqlite-automatic-build enables/disables local builds.
EmacSQL doesn't cover all of SQLite's features. Here are a list of things that aren't supported, and probably will never be.
Collating. SQLite has three built-in collation functions: BINARY (default), NOCASE, and RTRIM. EmacSQL values never have right-hand whitespace, so RTRIM won't be of any use. NOCASE is broken (ASCII-only) and there's little reason to use it.
Text manipulation functions. Like collating this is incompatible with EmacSQL s-expression storage.
Date and time. These are incompatible with the printed values stored by EmacSQL and therefore have little use.
EmacSQL is not intended to play well with other programs accessing the SQLite database. Non-numeric values are are stored encoded as s-expressions TEXT values. This avoids ambiguities in parsing output from the command line and allows for storage of Emacs richer data types. This is an efficient, ACID-compliant database specifically for Emacs.
Emacs Lisp Indentation Annoyance
emacs-lisp-mode indents vectors as if they were regular
;; Ugly indentation! (emacsql db [:select * :from people :where (> age 60)])
Calling the function
advises the major mode to fix this annoyance.
;; Such indent! (emacsql db [:select * :from people :where (> age 60)])
Contributing and Extending
You'll need to install Cask, which is required for compilation and unit testing.
If the environment variable
PGDATABASE is present then the unit
tests will also be run with PostgreSQL (emacsql-psql). Provide
PGUSER if needed. If
PGUSER is provided,
the pg.el backend (emacsql-pg) will also be tested.
If the environment variable
MYSQL_DBNAME is present then the unit
tests will also be run with MySQL in the named database. Note that
this is not an official MySQL variable, just something made up for
Creating a New Front-end
EmacSQL uses EIEIO so that interactions with a connection occur
through generic functions. You need to define a new class that
- Provide a constructor that initializes the connection and calls
emacsql-register(for automatic connection cleanup).
emacsql-typesif needed (hint: use a class-allocated slot).
- Ensure that you properly read NULL as nil (hint: ask your back-end to print it that way).
- Register all reserved words with
- Preferably provide
- Set the default isolation level to serializable.
- Enable autocommit mode by default.
- Prefer ANSI syntax (value escapes, identifier escapes, etc.).
- Enable foreign key constraints by default.
The goal of the autocommit, isolation, parsing, and foreign key configuration settings is to normalize the interface as much as possible. The connection's user should have the option to be agnostic about which back-end is actually in use.
The provided implementations should serve as useful examples. If your back-end outputs data in a clean, standard way you may be able to use the emacsql-protocol-mixin class to do most of the work.