Mojo Storage Database

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This page was created to help others by giving a basic example of creating a new database for your application and storing some data in it.


Contents

SQL Overview

It needs to be mentioned that SQLite (what HTML5 uses), is not as controlling as other databases. For one it's not going to give you an error when you insert text into an integer, or anything like that so regex all input for users or limit it in some way.

Data Type Example
INTEGER '0' '123' '3939'
REAL '1.1' '10.0'
TEXT 'foo' 'bar'
BLOB [binary data / images]
NULL absolutely nothing

Creating a Database and a Table

var name = "MyDB";  // required
var version = "0.1";  // required
var displayName = "My Mojo-Driven database"; // optional
var size = 200000;  // optional
 
var db = openDatabase(name, version, displayName, size);
 
if (!db) {
  Mojo.Log.error("Could not open database");
} else {
  var sql = "CREATE TABLE IF NOT EXISTS 'my_table' (id INTEGER PRIMARY KEY, num REAL, data TEXT)";  // check sqlite data types for other values
  db.transaction( function (transaction) {
    transaction.executeSql(sql,  // SQL to execute
                           [],    // array of substitution values (if you were inserting, for example)
                           function(transaction, results) {    // success handler
                             Mojo.Log.info("Successfully created table"); 
                           },
                           function(transaction, error) {      // error handler
                             Mojo.Log.error("Could not create table: " + error.message);
                           }
    );
  }.bind(this));
}

In order to use non-anonymous event handlers, the function supplied to db.transaction has to be bound to the current context, as in the following, modified example:

SceneAssistant.prototype.createMyTable = function(){
  var name = "MyDB";  // required
  var version = "0.1";  // required
  var displayName = "My Mojo-Driven database"; // optional
  var size = 200000;  // optional
 
  var db = openDatabase(name, version, displayName, size);
  if (!db) {
    Mojo.Log.error("Could not open database");
  } else {
    var sql = "CREATE TABLE IF NOT EXISTS 'my_table' (id INTEGER PRIMARY KEY, num REAL, data TEXT)";  // check sqlite data types for other values
    db.transaction(
      function (transaction) { 
        transaction.executeSql(sql, [],
          this.dbSuccessHandler.bind(this),
          this.dbErrorHandler.bind(this)); 
      }
    ).bind(this)); //this is important!
}
 
SceneAssistant.prototype.dbSuccessHandler = function(transaction, results){}
SceneAssistant.prototype.dbErrorHandler = function(transaction, errors){}

openDatabase

If you try to look for MyDB on the filesystem, you won't find it. The openDatabase method creates an entry in the Databases table in /var/usr/home/root/html5-databases/Databases.db which points to the actual location of your database. Note that the details in the Databases table are what you specified in openDatabase except version. Version is contained in the __WebKitDatabaseInfoTable__ table in the actual database.


In the examples contained in this page, the database that is created has a maximum storage capacity of 1 MB. If you need a larger database, then append ext: to the beginning of the database name. For example:

var db = openDatabase("ext:MyDB", "0.1");

This will create the database in /media/internal/.app-storage.

Inserting a Row

var myNum = 512.785;
var test = "I'm test data!";
 
var db = openDatabase("MyDB", "0.1"); // this is all that is required to open an existing DB
var sql = "INSERT INTO 'my_table' (num, data) VALUES (?, ?)";
 
db.transaction( function (transaction) {
  transaction.executeSql(sql,  [myNum, test], 
                         function(transaction, results) {    // success handler
                           Mojo.Log.info("Successfully inserted record"); 
                         },
                         function(transaction, error) {      // error handler
                           Mojo.Log.error("Could not insert record: " + error.message);
                         }
  );
});

Inserting Multiple Rows

With asynchronous database methods, you can really screw things up if you try to do too many transacations in rapid succession. Luckily, you can run as many executeSql methods inside a single transaction as you need.

var dataArray = [];
for(var i = 0; i < 100; i++) {
  dataArray[i] = i;
}
 
var db = openDatabase("MyDB", "0.1");
 
db.transaction( function (transaction) {
  for(var i=0; i < dataArray.length; i++) {
    var sql = "INSERT INTO 'my_table' (num, data) VALUES (?, ?)";
    transaction.executeSql(sql,  [dataArray[i], dataArray[i]], 
                           function(transaction, results) {    // success handler
                             Mojo.Log.info("Successfully inserted record"); 
                           },
                           function(transaction, error) {      // error handler
                             Mojo.Log.error("Could not insert record: " + error.message);
                           }
    );
  }
});

Retrieving Data

When a query returns results to the success handler, the rows are contained in .rows.

var db = openDatabase("MyDB", "0.1");
var sql = "SELECT * FROM 'my_table'";
 
db.transaction(function(transaction) {
  transaction.executeSql(sql, [],
                         function(transaction, results) {
                           // results.rows holds the rows returned by the query
                           var my_num = results.rows.item(0).num; // returns value of column num from first row
                         },
                         function(transaction, error) {
                           Mojo.Log.error("Could not read: " + error.message);
                         });
});

Extra Help

http://developer.apple.com/safari/library/documentation/iPhone/Conceptual/SafariJSDatabaseGuide/UsingtheJavascriptDatabase/UsingtheJavascriptDatabase.html

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