Trouble reading sqlite3 database columns of type blob with sql.js - sqlite

Question

So i am using the sql.js library i.e. the port of sqlite in javascript which can be found here https://github.com/kripken/sql.js.
This is my code to open and read the database that comes from a flat file store locally.
First the file a local file is selected via this HTML
<input type="file" id="input" onchange="handleFiles(this.files)">
The js code behind the scenes is as follows,
function handleFiles(files) {
var file = files[0];
var reader = new FileReader();
reader.readAsBinaryString(file);
openDbOnFileLoad(reader);
function openDbOnFileLoad(reader){
setTimeout(function () {
if(reader.readyState == reader.DONE) {
//console.log(reader.result);
db = SQL.open(bin2Array(reader.result));
execute("SELECT * FROM table");
} else {
//console.log("Waiting for loading...");
openDbOnFileLoad(reader);
}
}, 500);
}
}
function execute(commands) {
commands = commands.replace(/\n/g, '; ');
try {
var data = db.exec(commands);
console.log(data);
} catch(e) {
console.log(e);
}
}
function bin2Array(bin) {
'use strict';
var i, size = bin.length, ary = [];
for (i = 0; i < size; i++) {
ary.push(bin.charCodeAt(i) & 0xFF);
}
return ary;
}
Now this works and i can access all the columns and values in the database, however there is one column which is of type blob and that just shows up as empty. Any ideas of how i can access the contents of this blob?
The correct answer!
So what I was trying to ask in this question is simply how to read the contents of a column of type blob using sql.js. The correct answer is to specify the column names in the question and for the column that contains data of type blob, get its contents using the hex function i.e. select column1,hex(column2) from table. It was by no means a question about the most efficient way of doing this. I have also written a blog post about this.

Answer 1

Here is a slightly modified copy of the function responsible for initializing my sqlite database:
sqlite.prototype._initQueryDb = function(file, callback) {
self = this;
var reader = new FileReader();
// Fires when the file blob is done loading to memory.
reader.onload = function(event) {
var arrayBuffer = event.target.result,
eightBitArray = new Uint8Array(arrayBuffer),
database = SQL.open(eightBitArray);
self._queryDb = database;
// Trigger the callback to the calling function
callback();
}
// Start reading the file blob.
reader.readAsArrayBuffer(file);
}
In this case, file is a local sqlite database handle that I get from an HTML input element. I specify a function to call when a change event happens to that input and get the blob from the resulting event.target.files[0] object.
For the sake of brevity on my part I left some things out but I can throw together a smaller and more simplified example if you are still struggling.

Answer 2

The answer is: with kripken's sql.js, that you mentioned above you can't. At least as of today (may 2014). The original author doesn't maintain sql.js anymore.
However, I'm the author of a fork of sql.js, that is available here: https://github.com/lovasoa/sql.js .
This fork brings several improvements, including support for prepared statements, in which, contrarily to the original version, values are handled in their natural javascript type, and not only as strings.
With this version, you can handle BLOBs (both for reading and writing), they appear as Uint8Arrays (that you can for instance convert to object URL to display contents to your users).
Here is an example of how to read blob data from a database:
var db = new SQL.Database(eightBitArray); // eightBitArray can be an Uint8Array
var stmt = db.prepare("SELECT blob_column FROM your_table");
while (stmt.step()) { // Executed once for every row of result
var my_blob = stmt.get()[0]; // Get the first column of result
//my_blob is now an Uint8Array, do whatever you want with it
}
db.close(); // Free the memory used by the database
You can see the full documentation here: http://lovasoa.github.io/sql.js/documentation/