Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/nicferrier/emacs-db

very simple database for emacslisp, can also wrap other databases.
https://github.com/nicferrier/emacs-db

Last synced: 7 days ago
JSON representation

very simple database for emacslisp, can also wrap other databases.

Awesome Lists containing this project

README 

        
= Emacs Db - Key/Values stores for Emacs =



An EmacsLisp interface to key/value stores (Mongo, Postgresql Hstore,

etc..) with a simple default implementation based on EmacsLisp Hashtables.



== The interface ==



The idea behind this is to make an interface for interacting with

simple key/value database stores that is portable across all such

stores. So you can make code once but swap out the database with

relative ease.



The interface includes the following functions:



=== db-make reference ===



Make a DB based on the //reference//.



=== db-get key db ===



Get the value from the //db// with the //key//.



=== db-put key value db ===



Put a new //value// into the //db// with the specified //key//.



Return the //value// as it has been put into the //db//.



=== db-map func db &optional query filter ===



Call //func// for every record in //db// optionally //query// filter.



//query//, if specified, should be a list of query terms.



//func// should take 2 arguments:



{{{

  key db-value

}}}



where the DB-VALUE is whatever the //db// has attached to the

specified KEY.



This returns an alist of the KEY and the value the function

returned.  If //filter// is [[t]] then only pairs with a value are

returned.



=== db-query db query ===



Do //query// on //db// and return the result.



This is [[db-map]] with an identity function.



== Query language ==



{{{db}}} uses the query language provided by the {{{kv}}} library,

which is implemented as a mapping function test on ever value by the

persistent hashtable implementation.



The language should be translatable to just about any database query

language (Mongo, SQL, etc...).



There are only 3 constructs currently, {{{|}}}, {{{&}}} and {{{=}}}.



An expression could be:



{{{

(= field-name value)

}}}



To select any record where {{{field-name}}} has the {{{value}}}



{{{

(|(= field-name value)(= other-field other-value))

}}}



To select any record where {{{field-name}}} has the {{{value}}} 

or {{{other-field}}} has the value {{{other-value}}}



{{{

(&(= field-name value)(= other-field other-value))

}}}



To select any record where {{{field-name}}} has the {{{value}}} 

and {{{other-field}}} has the value {{{other-value}}}.



Logical combinations of {{{|}}} and {{{&}}} are also possible.



== Hashtable implementation ==



{{{db}}} comes with a simple implementation which can store any

EmacsLisp object (though alists would most usually be preferred).



To make a {{{db}}} with the hash implementation:



{{{

(db-make 

  `(db-hash 

     :filename ,(format "/var/cache/some-file")))

}}}



Obviously, most often you will assign the db to a global variable.



{{{

(defvar my-db 

  (db-make 

   `(db-hash 

     :filename ,(format "/var/cache/some-file"))))



(db-put "001" '(("a" . 10)("b" . 20)) my-db)

(db-put "002" '(("a" . 17)("b" . "hello")("xyz" . "well!")) my-db)

(db-get "002" my-db)

}}}



results in:



{{{

(("a" . 17)("b" . "hello")("xyz" . "well!"))

}}}



=== Testing ===



Hash Db's are tied to filenames so to test them you often have to

manage that persistence:



{{{

(unwind-protect

     (let ((mydb (db-make `(db-hash :filename "/tmp/mydb")))

           (json 

             (with-temp-buffer

              (insert-file-contents "~/work/elmarmalade/users-mongo.json")

              (goto-char (point-min))

              (json-read))))

       (--each json (db-put (car it) (cdr it) mydb))

       (list (db-get 'triss mydb)

             (db-get 'nicferrier mydb)))

  (delete-file "/tmp/mydb.elc"))

}}}



Note the deleting of the {{{elc}}} file. That's how the hash db is

stored. 



Alternately one could use {{{fakir-file}}} (see the fakir package) to

mock the file system. But that's harder than just creating and

throwing away the file.