Sqlite: check if database exist

Question

I am developing a mobile application using phonegap that store some data into the local database (sqlite DB). I need to know if the database exist or not, and that to determ

Answer 1

I don't think that you can check for the existence of the DB directly. I've researched and haven't found a way to do it using a simple function call. However, this seems to be a popular request, and here's a workaround:

var db = window.openDatabase("my.db", "1", "Demo", -1);


db.transaction(function (tx) {

/*I don't think that there is a way to check if a database exists.
    As I think that the openDatabase call above will just create
    a missing DB. Here is a second-best way to do it - there 
    is a way to check to see if a table exists.  Just pick a table that 
    your DB should have and query it.  If you get an ERROR, then you 
    can assume your DB is missing and you will need to create it. */

console.log("Trying to get the test data");
tx.executeSql("select * from test_table", [], function (tx, res) {

    var len = res.rows.length, i;
    for (i = 0; i < len; i++) {
        console.log(res.rows.item(i).data);
    }
}, function (err) {
    console.log("Error selecting: " + err);

    //NOW we need to create the DB and populate it
    tx.executeSql('CREATE TABLE IF NOT EXISTS test_table (id integer primary key, data text)');

    tx.executeSql('INSERT INTO test_table (data) VALUES("test data one")');
    tx.executeSql('INSERT INTO test_table (data) VALUES("test data two")');

    //now test select
    tx.executeSql("select * from test_table", [], function (tx, res) {

        var len = res.rows.length, i;
        for (i = 0; i < len; i++) {
            console.log(res.rows.item(i).data);
        }
    });


    //now clean up so we can test this again
    tx.executeSql('DROP TABLE IF EXISTS test_table', [], function (tx, res) {
        console.log("dropped table");
    }, function (err) {
        console.log("Error dropping table: " + err);
    });

});
});

As you can see, the error function during the first query will create and populate the DB. It's using exception handling for program logic flow, but it works!

Answer 2

I needed to do something similar, I needed to check if the application had a db already created (legacy DB) and if so export all the data to the new db (new and improved DB) and then delete this DB.

Background Info: I was moving from simple keyvalue tables to complex relational DB with cascades etc.

function onDeviceReady() {
    // CHECK IF LEGACY DATABASE EXISTS. IF DOES EXPORT EXISTING DATA TO NEW DB THEN DELETE LEGACY
    window.resolveLocalFileSystemURL(cordova.file.applicationStorageDirectory + "/databases/<DatabaseName>.db", exportToNewDB, setupDB);
}

Note: If file exists (success), then we need to do our export code in here, then delete file so this method will always fail. If file doesn't exist - user has already exported to new DB or they our new user and never had legacy DB.

// Fail Method
function setupDB() {
    newDB = window.sqlitePlugin.openDatabase({ name: "<NewImprovedDBName>.db" });
    newDB.transaction(sql.initDB, sql.errorCallback, sql.successCallBack);
}
// Success Method
function exportToNewDB() {
    db = window.sqlitePlugin.openDatabase({ name: "<LegacyDBName>.db" });
    db.transaction(function (tx) {
         setupDB();
         // Insert Export code Here

         // Delete DB
         window.sqlitePlugin.deleteDatabase("<LegacyDBName>.db", sqlSuccess, sqlFail);
    }, sqlFail);
}

Answer to your Question:

window.resolveLocalFileSystemURL(cordova.file.applicationStorageDirectory + "/databases/my_db.db", process_1, process_2);

Answer 3

The best way for determining if the DB exists or not is to check if the file that represents it exists. This is a simple IO operation, like the following example:

string path = Path.Combine(ApplicationData.Current.LocalFolder.Path, databaseName);

if (File.Exists(path)) { //your code here }