Hello I am having problems with testing if my embedded datbase exists.
I created a database like follows:
try {
SQLiteConnection.CreateFile("AttendanceDatabase.sqlite");
} catch (SQLiteException ex) {
}
And then I insert tables and data into the tables, everything works fine. When im saving data to the database im using the the connection string as follows:
conn = new SQLiteConnection("Data Source=AttendanceDatabase.sqlite;Version=3;");
Now my problem is everytime I run my program it creates the database over, and I would like to know how to test if the database exists it should not create the database over again.
I see the recomended way to do it is using the next statement:
if (File.Exists())
{
}
and I have tried using it as follows:
if (File.Exists("Data Source=AttendanceDatabase.sqlite;Version=3;")){
MessageBox.Show("File Exists");
}
but it does not want to go into the if brackets and display "File Exists".
So I would like to know what my path should be for my embedded database, that is if thats where my problem lies?
Thanx in advance!
I don't have a ton of context but if you update your check:
var basePath = "C:/<path to file>/";
if (File.Exists(basePath + "AttendanceDatabase.sqlite")){
MessageBox.Show("File Exists");
}
You might have more luck. If you give me more context to how you are running this I can help you with using services to lookup the file path. You can look it up based on assembles, approot, etc.
Related
I have following C# code in a console application.
Whenever I debug the application and run the query1 (which inserts a new value into the database) and then run query2 (which displays all the entries in the database), I can see the new entry I inserted clearly. However, when I close the application and check the table in the database (in Visual Studio), it is gone. I have no idea why it is not saving.
using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlServerCe;
using System.Data;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
try
{
string fileName = "FlowerShop.sdf";
string fileLocation = "|DataDirectory|\\";
DatabaseAccess dbAccess = new DatabaseAccess();
dbAccess.Connect(fileName, fileLocation);
Console.WriteLine("Connected to the following database:\n"+fileLocation + fileName+"\n");
string query = "Insert into Products(Name, UnitPrice, UnitsInStock) values('NewItem', 500, 90)";
string res = dbAccess.ExecuteQuery(query);
Console.WriteLine(res);
string query2 = "Select * from Products";
string res2 = dbAccess.QueryData(query2);
Console.WriteLine(res2);
Console.ReadLine();
}
catch (Exception e)
{
Console.WriteLine(e);
Console.ReadLine();
}
}
}
class DatabaseAccess
{
private SqlCeConnection _connection;
public void Connect(string fileName, string fileLocation)
{
Connect(#"Data Source=" + fileLocation + fileName);
}
public void Connect(string connectionString)
{
_connection = new SqlCeConnection(connectionString);
}
public string QueryData(string query)
{
_connection.Open();
using (SqlCeDataAdapter da = new SqlCeDataAdapter(query, _connection))
using (DataSet ds = new DataSet("Data Set"))
{
da.Fill(ds);
_connection.Close();
return ds.Tables[0].ToReadableString(); // a extension method I created
}
}
public string ExecuteQuery(string query)
{
_connection.Open();
using (SqlCeCommand c = new SqlCeCommand(query, _connection))
{
int r = c.ExecuteNonQuery();
_connection.Close();
return r.ToString();
}
}
}
EDIT: Forgot to mention that I am using SQL Server Compact Edition 4 and VS2012 Express.
It is a quite common problem. You use the |DataDirectory| substitution string. This means that, while debugging your app in the Visual Studio environment, the database used by your application is located in the subfolder BIN\DEBUG folder (or x86 variant) of your project. And this works well as you don't have any kind of error connecting to the database and making update operations.
But then, you exit the debug session and you look at your database through the Visual Studio Server Explorer (or any other suitable tool). This window has a different connection string (probably pointing to the copy of your database in the project folder). You search your tables and you don't see the changes.
Then the problem get worse. You restart VS to go hunting for the bug in your app, but you have your database file listed between your project files and the property Copy to Output directory is set to Copy Always. At this point Visual Studio obliges and copies the original database file from the project folder to the output folder (BIN\DEBUG) and thus your previous changes are lost.
Now, your application inserts/updates again the target table, you again can't find any error in your code and restart the loop again until you decide to post or search on StackOverflow.
You could stop this problem by clicking on the database file listed in your Solution Explorer and changing the property Copy To Output Directory to Copy If Newer or Never Copy. Also you could update your connectionstring in the Server Explorer to look at the working copy of your database or create a second connection. The first one still points to the database in the project folder while the second one points to the database in the BIN\DEBUG folder. In this way you could keep the original database ready for deployment purposes and schema changes, while, with the second connection you could look at the effective results of your coding efforts.
EDIT Special warning for MS-Access database users. The simple act of looking at your table changes the modified date of your database ALSO if you don't write or change anything. So the flag Copy if Newer kicks in and the database file is copied to the output directory. With Access better use Copy Never.
Committing changes / saving changes across debug sessions is a familiar topic in SQL CE forums. It is something that trips up quite a few people. I'll post links to source articles below, but I wanted to paste the answer that seems to get the best results to the most people:
You have several options to change this behavior. If your sdf file is part of the content of your project, this will affect how data is persisted. Remember that when you debug, all output of your project (including the sdf) if in the bin/debug folder.
You can decide not to include the sdf file as part of your project and manage the file location runtime.
If you are using "copy if newer", and project changes you make to the database will overwrite any runtime/debug changes.
If you are using "Do not copy", you will have to specify the location in code (as two levels above where your program is running).
If you have "Copy always", any changes made during runtime will always be overwritten
Answer Source
Here is a link to some further discussion and how to documentation.
I am trying my hands on Windows phone 8 applications and I am stuck into a weird situation here. I am using sqlite in order to create sqlite db and add values into the database. I am able to create the database and add the values in the database successfully but I am having a weird situation here.
Everytime I close the emulator and start the project again the database gets created again which should not be happening because I created the db the very first time I run the application.
Does anybody know why, and how I can prevent it from recreating the database each time?
public string DB_PATH = Path.Combine(Path.Combine(ApplicationData.Current.LocalFolder.Path, "aa.sqlite"));
private SQLiteConnection dtCon;
public MainPage()
{
InitializeComponent();
CreateDatabase();
dtCon = new SQLiteConnection(DB_PATH);
var tp = dtCon.Query<Contacts>("select * from contacts").ToList();
}
private async void CreateDatabase()
{
bool isDatabaseExisting = false;
//Checking if database already exists
try
{
Windows.Storage.StorageFile storagefile = await Windows.Storage.ApplicationData.Current.LocalFolder.GetFileAsync("aa.sqlite");
isDatabaseExisting = true;
}
catch
{
isDatabaseExisting = false;
}
//if not exists then creating database
if (!isDatabaseExisting)
{
String str = System.IO.Path.Combine(Windows.Storage.ApplicationData.Current.LocalFolder.Path, "sqlite.db");
AddDataToDB(DB_PATH);
}
}
private void AddDataToDB(string str)
{
// Create the database connection.
dtCon = new SQLiteConnection(str);
// Create the table Task, if it doesn't exist.
dtCon.CreateTable<Contacts>();
Contacts oContacts = new Contacts();
oContacts.Name = "dfgdf";
oContacts.Detail = "asdfsf";
dtCon.Insert(oContacts);
}
I'm pretty sure when you close your emulator and restart, you're basically just uninstalling the application. Which is why your files or not there anymore -- as it looks like you're storing your data in isolated storage. I do not know if there is anyway around this.
You can buy a very cheap Windows 8/8.1 Phone and the files will persist until you manually uninstall the test application.
As #Chubosaurus says, closing and re-opening the emulator will remove all the apps. You can generally keep it running as long as you want and keep re-deploying your app to the emulator (although obviously rebooting the host PC will kill it).
You can save and restore the data from your emulator image via the ISETool command. See more here
Try adding Console.WriteLine("True"); and Console.WriteLine("False"); into the expected places after checking isDatabaseExisting to see/understand what the code path really is.
I am trying to create a Sqlite database using Monotouch 3.0.3.4. Everything works fine on the iPhone simulator, but I get the following error on the test iPhone:
DataLayer.CreateDatabase Exception: System.UnauthorizedAccessException: Access to the path "/private/var/mobile/Applications/4B4944BB-EC37-4B0C-980C-1A9B60DACB44/TestApp.app/myDatabase.db3" is denied.
Here is the code I am using:
// creates database and tables if they do not exist.
public void CreateDatabase ()
{
string sql = string.Empty;
string dbFileName = "myDatabase.db3";
try {
if (!File.Exists (dbFileName)) {
// create database
SqliteConnection.CreateFile (dbFileName); //This is where the error occurs
Console.WriteLine ("CreateDatabase: Database created.");
...
}
catch (Exception ex) {
Console.WriteLine ("CreateDatabase Exception: " + ex.ToString ());
}
...
I have also tried specifing the personal folder, but that has no effect. What do I need to do to make sure permissions are correct?
Thanks!
Monotouch 3.0.3.4
That's likely MonoDevelop 3.0.3.4. See About MonoDevelop to get the MonoTouch version.
"/private/var/mobile/Applications/4B4944BB-EC37-4B0C-980C-1A9B60DACB44/TestApp.app/myDatabase.db3"
On devices the applications are signed, so their content can't change (without breaking the signature). As such you're not allowed to change things in the .app directory.
You should create (or copy) the database in the Documents directory and then open the database as read-write.
See the linked article for more details.
We noticed a slight oddity in the Sitecore API code. The code is below for your reference. The code is trying to get a database by doing new Database(database). But randomly it was failing.
This code worked for a while with Database db = new Database(database); but started failing randomly yesterday. When we changed the code to Database db = Database.GetDatabase(database);, the code started working again. What is the difference between the two approaches and what is recommended by Sitecore?
I've seen this happen twice now - multiple times in production and a couple of times in my development environment.
public static void DeleteItem(string id, stringdatabase)
{
//get the database
Database db = new Database(database);
//get the item
item = db.GetItem(new ID(id));
if (item != null)
{
using(new Sitecore.SecurityModel.SecurityDisabler())|
{
//delete the item
item.Delete();
}
}
}
A common way you will see people get a specific database is:
Sitecore.Data.Database master = Sitecore.Configuration.Factory.GetDatabase("master");
This is equivalent to Sitecore.Data.Database.GetDatabase("master").
When you call either of these methods it will first check the cache for the database. If not found it will build up the database with all of the configuration values within the config file via reflection. Once the database is created it will be placed in the cache for future use.
When you use the constructor on the database it is simply creating a rather empty database object. I am rather suprised to hear it was working at all when you used this method.
The proper approach to get a specific database would be to use:
Sitecore.Configuration.Factory.GetDatabase("master");
// or
Sitecore.Data.Database.GetDatabase("master");
If you are looking to get the database used with the current request (aka context database) you can use Sitecore.Context.Database. You can also use Sitecore.Context.ContentDatabase.
I'm trying to write to a local SQLite database using the flash.data.* classes in AIR. I'm opening a synchronous connection in CREATE mode and using the begin() and commit() methods to execute the queries. Everything seems to be executing as expected. The query execute() and connection commit() method's success handler is being called, the connection object's totalChanges property is being incremented, everything looks good except the database file is not being written to. Any ideas what I could be doing wrong?
I don't think it's related to...
the query itself since that was
throwing errors whenever something
didn't match up.
the file mode for the same reason.
file permissions - currently set to 777
Simplified version of the code:
var database:File = new File(File.applicationDirectory.nativePath + "//" + PATH_TO_DB );
var connection:SQLConnection = new SQLConnection();
connection.open( database, SQLMode.CREATE );
connection.begin();
var statement:SQLStatement = new SQLStatement();
statement.sqlConnection = connection;
statement.addEventListener(SQLEvent.RESULT, onQueryResult);
statement.addEventListener(SQLErrorEvent.ERROR, onQueryError);
statement.text = "INSERT INTO myCrazyTable (foo) VALUES ('bar')";
statement.execute();
connection.commit(new Responder(onCommitComplete));
function onQueryResult(event:SQLEvent):void {
trace("Query successful"); // this is getting called
}
function onQueryError(event:SQLErrorEvent):void {
trace("Error in query: " + event.error.message);
}
function onCommitComplete(event:SQLEvent):void {
trace("Commit Success"); // this is getting called
connection.close();
}
// Database isn't getting touched.
Did you check options defined by pragma? For example http://www.sqlite.org/pragma.html#pragma_synchronous can cause this behavior.
The first thing I would ask is, how do you know it isn't being touched? Timestamp? Or are you querying for the item and not finding it?
The main reason I ask is, I'm suspicious of this code:
var database:File = new File(File.applicationDirectory.nativePath + "//" + PATH_TO_DB );
I think the // is incorrect, and I think possibly your DB is ending up somewhere other than where you think it is, most likely at the root filesystem. If my theory is correct, you are writing data to a different db than you think you are, not just "in memory".
I fixed the issue. I ended up rewriting the code for accessing the database. I'm not sure exactly where the problem was, something I must have been overlooking. Thanks for everyone's help.