LuaJIT FFI binding to the Sophia database
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README.md

LJIT2Sophia

Overview

LuaJIT FFI binding to the Sophia (1.1) database: http://sphia.org

The sophia database is a relatively new (September, 2013) key value store which is small and embeddable. This LuaJIT binding seems appropriate.

The Sophia API has changed dramatically since the 1.1 version. The 1.1 compatible version of this LuaJIT binding will be saved off as a 'release' and no further work will be done on it.

A 1.2 version of the binding is in the works, so the files currently checked in represent that work in progress.

All the documentation below corresponds to the 1.1 version of the API. Some or all of it might change for the 1.2 binding.

API Access

The binding gives you access to the component at two distinct levels. If you want to use sophia in a style similar to what you would do using the 'C' language, then you can simply do this:

sophia_ffi = require("sophia_ffi");
sophia_ffi.sp_env();
sophia_ffi.sp_db(...);

All of the functions are accessible through a simple table interface. If you would like to promote them to the global namespace, then call: sophia_ffi.promoteToGlobal(). If you do this, you can write code that looks almost identical to 'C' code.

Object Oriented Access

This is Lua, and the better way to access sophia is using more lua like semantics and constructs. An object model is presented, which makes it relatively easy to manipulate sophia databases.

To create and/or open a database, simply call the constructor on the SophiaDatabase object. This will open up an existing database, or create it anew if it does not exist.

local sophia = require("sophia")
local db, err = sophia.SophiaDatabase("./db");

inserting a value

Once you have a database object, there are two ways to get values into it. The 'set()' method mimics the standard 'C' interface function, so you must pass all 4 parameters.

local success, err = db:set(keybuff, ffi.sizeof(keybuff), value, #str); 

The 'upsert()' method allows you to set a value using a simple key/value pair, which are assumed to be lua string objects.

local success, err = db:upsert(key, value)

For this upsert operation, if the value does not exist in the database, it will be added. If the key already exists, then the value for that key will be changed to the value being presented.

retrieving a value

There are two ways to retrieve a value from the database. The first mimics the standard 'C' interface function, and requires 4 parameters.

local success, err = db:get(keybuff, ffi.sizeof(keybuff), value, valuesize);

The second mechnism allows you to specify a single parameter, which is the key associated with the value you want to retrieve. A second 'keysize' parameter is allowed, but if it is not supplied, the #key length will be used.

local value, err = db:retrieve(key, keysize)

Upon completion, the 'value' will contain the value specified by the key. Otherwise, it will return false, and the associated error.

Using a cursor to iterate over the entire database

In addition to retrieving single values at a time, you can iterate over a range of values in the database.

for key, keysize, value, valuesize in db:iterate() do

    print(ffi.cast("int *",key)[0]);

    print(ffi.string(value, valuesize));

end

Rather than follow the approach of simply creating objects to wrap groupings of APIs, the binding presents what seems to make the most sense from a usability standpoint.

The SophiaDatabase object is the primary interaction point. The SophiaEnvironment is a secondary player, which is used by the SophiaDatabase internally, but for the most part is hidden.

The Database:iterate() function has the following signature:

SophiaDatabase.iterate = function(self, key, keysize, sporder)
    keysize = keysize or 0;
    sporder = sporder or ffi.C.SPGTE;

In this way, by default, the iterator will iterate over the entire database, from the beginning. The next logical thing the user is likely to want is to iterate from a specific point, so the key value is the first parameter. Lastly, they might want to specify an order. The thinking is, if they're specifying an order, then they MUST also specify a key, so the odering can come last.

Using an iterator is natural for a lua program, so that's the choice. Of course, you can use the lower level sophia_ffi calls and create whatever specialized interface you prefer, but this is the default set of convenience provided.

Going forward, the set/get/iterate methods could do a little bit of magic and assume things like lengths of lua strings can be inferred, and if the key is a 'number', it can be converted to a 4 or 8 byte value. this will make it a little bit convenient to work with these values without having to specify lengths explicitly.

LICENSE

This Software is licensed under the Microsoft Public License, which is a fairly straight forward open source license.

http://opensource.org/licenses/ms-pl

AUTHOR

William A Adams http://williamaadams.wordpress.com