localStorageDB - a simple, tiny database layer for localStorage

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localStorageDB is a simple layer over localStorage that provides a set of functions to store structured data like databases and tables. It provides basic insert/update/delete/query capabilities. localStorageDB has no dependencies, and is not based on WebSQL. Underneath it all, the structured data is stored as serialized JSON in localStorage.

A sample table 'books' in the database 'library'

id	title	author	year	copies
B001	Phantoms in the brain	Ramachandran	1999	10
B002	The tell-tale brain	Ramachandran	2011	10
B003	Freakonomics	Levitt and Dubner	2005	10

Creating a database, table, and populating the table

// Initialise. If the database doesn't exist, it is created
var lib = new localStorageDB("library");

// Check if the database was just created. Useful for initial database setup
if( lib.isNew() ) {

	// create the "books" table
	lib.createTable("books", ["id", "title", "author", "year", "copies"]);
	
	// insert some data
	lib.insert("books", {id: "B001", title: "Phantoms in the brain", author: "Ramachandran", year: 1999, copies: 10});
	lib.insert("books", {id: "B002", title: "The tell-tale brain", author: "Ramachandran", year: 2011, copies: 10});
	lib.insert("books", {id: "B003", title: "Freakonomics", author: "Levitt and Dubner", year: 2005, copies: 10});
	lib.insert("books", {id: "B004", title: "Predictably irrational", author: "Ariely", year: 2008, copies: 10});
	lib.insert("books", {id: "B005", title: "Tesla: Man out of time", author: "Cheney", year: 2001, copies: 10});
	lib.insert("books", {id: "B006", title: "Salmon fishing in the Yemen", author: "Torday", year: 2007, copies: 10});
	lib.insert("books", {id: "B007", title: "The user illusion", author: "Norretranders", year: 1999, copies: 10});
	lib.insert("books", {id: "B008", title: "Hubble: Window of the universe", author: "Sparrow", year: 2010, copies: 10});
	
	// commit the database to localStorage
	// all create/drop/insert/update/delete operations should be committed
	lib.commit();
}

Querying

// simple select queries
lib.query("books", {year: 2011});
lib.query("books", {year: 1999, author: "Norretranders"});

// select all books
lib.query("books");

// select all books published after 2003
lib.query("books", function(row) {	// the callback function is applied to every row in the table
	if(row.year > 2003) {		// if it returns true, the row is selected
		return true;
	} else {
		return false;
	}
});

// select all books by Torday and Sparrow
lib.query("books", function(row) {
	if(row.author == "Torday" || row.author == "Sparrow") {
		return true;
	} else {
		return false;
	}
});

Example results from a query

// query results are returned as arrays of object literals
// an ID field with the internal auto-incremented id of the row is also included
// thus, ID is a reserved field name

lib.query("books", {author: "ramachandran"});

/* results
[
 {
   ID: 1,
   id: "B001",
   title: "Phantoms in the brain",
   author: "Ramachandran",
   year: 1999,
   copies: 10
 },
 {
   ID: 2,
   id: "B002",
   title: "The tell-tale brain",
   author: "Ramachandran",
   year: 2011,
   copies: 10
 }
]
*/

Updating

// change the title of books published in 1999 to "Unknown"
lib.update("books", {year: 1999}, function(row) {
	row.title = "Unknown";
	
	// the update callback function returns to the modified record
	return row;
});

// add +5 copies to all books published after 2003
lib.update("books",
	function(row) {	// select condition callback
		if(row.year > 2003) {
			return true;
		} else {
			return false;
		}
	},
	function(row) { // update function
		row.year+=5;
		return row;
	}
);

Deleting

// delete all books published in 1999
lib.deleteRows("books", {year: 1999});

// delete all books published before 2005
lib.deleteRows("books", function(row) {
	if(row.year < 2005) {
		return true;
	} else {
		return false;
	}
});

lib.commit(); // commit the deletions to localStorage

Method	Arguments	Description
localStorageDB()	database_name	Constructor
isNew()		Returns true if a database was created at the time of initialisation with the constructor
drop()		Deletes a database, and purges it from localStorage
tableCount()		Returns the number of tables in a database
commit()		Commits the database to localStorage
serialize()		Returns the entire database as serialized JSON
tableExists()	table_name	Checks whether a table exists in the database
createTable()	table_name, fields	Creates a table - fields is an array of string fieldnames. 'ID' is a reserved fieldname.
dropTable()	table_name	Deletes a table from the database
truncate()	table_name	Empties all records in a table and resets the internal auto increment ID to 0
rowCount()	table_name	Returns the number of rows in a table
insert()	table_name, data	Inserts a row into a table and returns its numerical ID - data is an object literal with field-values Every row is assigned an auto-incremented numerical ID automatically
query()	table_name, query, limit	Returns an array of rows (object literals) from a table matching the query. - query is either an object literal or null. If query is not supplied, all rows are returned - limit is the maximum number of rows to be returned Every returned row will have it's internal auto-incremented id assigned to the variable ID
update()	table_name, query, update_function	Updates existing records in a table matching query, and returns the number of rows affected - query is an object literal or a function. If query is not supplied, all rows are updated - update_function is a function that returns an object literal with the updated values
deleteRows()	table_name, query	Deletes rows from a table matching query, and returns the number of rows deleted - query is either an object literal or a function. If query is not supplied, all rows are deleted

Kailash Nadh