Ok, I've probably dug up the entire Google land and still couldn't find anything that could possibly answer my question.
I have my little foo method that does some deleting like this:
private void foo()
{
jdbcNamedParameterTemplate.update(sqlString, params); //1
jdbcNamedParameterTemplate.update(sqlString2, params2); //2
}
sqlString and sqlString2 are just delete statements like "Delete * from FooBar".
So when I get to the second call to update, do I have any guarantee that whatever operation the first one invokes in the database has already finished?
If you do that two in one session, and non multithreading, then yes the first one invokes in the database has already finished before the second update.
But if not in the same session you can check the version to check if the object already changed or not
int oldVersion = foo.getVersion();
session.load( foo, foo.getKey() ); // load the current state
if ( oldVersion != foo.getVersion()) { .... }// if true then the object has been changed
Related
I am trying to update data to a mySQL database using JPA. I have no problem persisting data but flush will not work as expected. I retrieve the id for the login session, set that id (it is the primary key) along with setting the description field that I want merged to the database. I have debugged line by line through this method and all variables contain the expected values. Any ideas or suggestions to overcome this problem are appreciated.
public String update() {
factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
EntityManager em = factory.createEntityManager();
if(true){
em.getTransaction().begin();
String sessionEmail=Util.getEmail();
//Create query to find user passwords matching the inputted name
Query myQuery = em.createQuery("SELECT u FROM BusinessAccount u WHERE u.email=:email");
myQuery.setParameter("email", sessionEmail);
List<BusinessAccount> accounts=myQuery.getResultList();
int intId=accounts.get(0).getId();
businessAccount.setId(intId);
String des=businessAccount.getDescription();
businessAccount.setDescription(des);
em.flush();
addMessage(new FacesMessage(FacesMessage.SEVERITY_INFO,
"User Registration Successful!", null));
return "success";
}
else {
addMessage(new FacesMessage(FacesMessage.SEVERITY_ERROR,
"User Registration Failed!", null));
return "failure";
}
}
merge() persists all the state of the entity. Not just the non-null fields. I it wasn't, you would complain that you want to set some field to null and that merge() ignores it and leaves it as is.
So get an entity from the database, and modify it, instead of only gettings its ID, creating a new entity instance from scratch and only settings some of its fields.
Note that, if you get the entity and modify it inside a single transaction, you don't even have to call merge(): the new state will be made persistent automatically.
I have constructed a function where two queries are performed. Both of these queries insert data into two separate tables, data that is related to the registration of a user.
In one table things like username,password are held and in the other table stuff like address, phone etc...
Here is the function:
function register_biz_user($post,$connection)
{
$name=$connection-> real_escape_string($_POST['name']);
$lastname= $connection->real_escape_string($_POST['lastname']);
$pass_hashed = password::hash($_POST['password']);
$passwd= $connection->real_escape_string($pass_hashed);
$buztype= $connection->real_escape_string($_POST['buztype']);
$usertype= $connection->real_escape_string($_POST['usertype']);
$address= $connection->real_escape_string($_POST['address']);
$city= $connection->real_escape_string($_POST['city']);
$municipality= $connection->real_escape_string($_POST['municipality']);
$url= $connection->real_escape_string($_POST['wwwaddress']);
$email= $connection->real_escape_string($_POST['e-mail']);
$phone= $connection->real_escape_string($_POST['phone']);
$hash =$connection->real_escape_string(md5( rand(0,1000) )) ;
$connection->set_charset("utf8");
$result1 = $connection->query("insert into users values
(NULL,'" .$name. "','" .$lastname . "','".$email."','". $passwd."','".
$hash."','". $usertype."')");
if (!$result1) {
throw new Exception('error');
return false;
}
else{$result2=$connection->query("insert into business_users values
('".$connection->insert_id."','" .$address."','".$url ."','".$phone.
"','".$city. "','".$municipality. "','".$buztype. "')");
}
if(!$result2)
{ throw new Exception('error');
return false;}
return true;
}
And here is my problem:
If you look at the code you might notice that there is the problem that the 1st query runs without problem and the second throws an exception or vice verca.
My point is that there is the danger that the db WILL have ONLY partial data of the registered user. The goal is that either both queries run successfully or none runs.
How I must write the above code such that I can achieve the above statement?
I hope I was clear enough.
Use transactions: http://dev.mysql.com/doc/refman/5.0/en/commit.html
BEGIN
... queries ...
COMMIT or ROLLBACK
Note: "or vice verca" - that's not possible. In that case the 2nd query never gets executed.
Note2:
what's $post? seems to be unused.
why don't you use prepared statements? escaping everyhing is very error prone.
why do you have a procedural interface, passing $connection? you should have objects which know about the database connections... you have mixed code for at least 3 different layers... not necessary bad if you plan to create write-once-get-rid-of-code but probably not a good idea for a project which you have to maintain for months/years.
I was able to store functions into a table. But now I have no idea of how to invoke them. The final table will have about 100 calls, so if possible, I'd like to invoke them as if in a foreach loop. Thanks!
Here is how the table was defined:
game_level_hints = game_level_hints or {}
game_level_hints.levels = {}
game_level_hints.levels["level0"] = function()
return
{
[on_scene("scene0")] =
{
talk("hint0"),
talk("hint1"),
talk("hint2")
},
[on_scene("scene1")] =
{
talk("hint0"),
talk("hint1"),
talk("hint2")
}
}
end
Aaand the function definitions:
function on_scene(sceneId)
-- some code
return sceneId
end
function talk(areaId)
-- some code
return areaId
end
EDIT:
I modified the functions so they'll have a little more context. Basically, they return strings now. And what I was hoping to happen is that at then end of invoking the functions, I'll have a table (ideally the levels table) containing all these strings.
Short answer: to call a function (reference) stored in an array, you just add (parameters), as you'd normally do:
local function func(a,b,c) return a,b,c end
local a = {myfunc = func}
print(a.myfunc(3,4,5)) -- prints 3,4,5
In fact, you can simplify this to
local a = {myfunc = function(a,b,c) return a,b,c end}
print(a.myfunc(3,4,5)) -- prints 3,4,5
Long answer: You don't describe what your expected results are, but what you wrote is likely not to do what you expect it to do. Take this fragment:
game_level_hints.levels["level0"] = function()
return
{
[on_scene("scene0")] =
{
talk("hint0"),
}
}
end
[This paragraph no longer applies after the question has been updated] You reference on_scene and talk functions, but you don't "store" those functions in the table (since you explicitly referenced them in your question, I presume the question is about these functions). You actually call these functions and store the values they return (they both return nil), so when this fragment is executed, you get "table index is nil" error as you are trying to store nil using nil as the index.
If you want to call the function you stored in game_level_hints.levels["level0"], you just do game_level_hints.levels["level0"]()
Using what you guys answered and commented, I was able to come up with the following code as a solution:
asd = game_level_hints.levels["level0"]()
Now, asd contains the area strings I need. Although ideally, I intended to be able to access the data like:
asd[1][1]
accessing it like:
asd["scene0"][1]
to retrieve the area data would suffice. I'll just have to work around the keys.
Thanks, guys.
It's not really clear what you're trying to do. Inside your anonymous function, you're returning a table that uses on_scene's return value as keys. But your on_scene doesn't return anything. Same thing for talk.
I'm going to assume that you wanted on_scene and talk to get called when invoking each levels in your game_level_hints table.
If so, this is how you can do it:
local maxlevel = 99
for i = 0, maxlevel do
game_level_hints.levels["level" .. i] = function()
on_scene("scene" .. i)
talk("hint" .. i)
end
end
-- ...
for levelname, levelfunc in pairs(game_level_hints.levels) do
levelfunc()
end
I'm using C#4.0 in a simple expense recording app. I'm trying to save to a table with an auto incremented id field, set as the primary key. It works fine the first time I use it, but the second and subsequent time, I get the "Cannot add an identity that already exists" error.
Here's the code I'm having trouble with
public bool SaveClaim(Claim newClaim, bool blNew)
{
bool blSuccess = true;
try
{
expContext.Claims.InsertOnSubmit(newClaim);
expContext.SubmitChanges();
claim = null;
}
catch (Exception e)
{
blSuccess = false;
MessageBox.Show(e.ToString());
}
return blSuccess;
}
I've been working on this all morning, and it's driving me daft. I'd be glad for any help.
Ensure you have the following properties set in your dbml for the identity column of Claim:
Auto Generated Value = true
Auto-Sync = OnInsert
Also ensure that your new Claim object is actually a new object, and not a reuse of the one you previously added.
Maybe you should try updating your designer.
Remove the table Claim, update the server explorer, and add it again.
At least that's what I do when I get this error. It usually shows when I set the identity column on the database after compiling.
Maybe you are trying to UPDATE newClaim using the INSERT method.
If newClaim has an ID and the method expContext.Claims.InsertOnSubmit(newClaim) is trying to insert a record with that ID. That could be the issue.
if (blNew)
expContext.Claims.InsertOnSubmit(newClaim);
else
expContext.Claims.UpdateOnSubmit(newClaim); //-- Assumed method
Additional
Here is a useful thread: MSDN Forums
if (blNew)
{
expContext.Claims.InsertOnSubmit(newClaim);
}
Hallo,
I have web service that has multiple methods that can be called. Each time one of these methods is called I am logging the call to a statistics database so we know how many times each method is called each month and the average process time.
Each time I log statistic data I first check the database to see if that method for the current month already exists, if not the row is created and added. If it already exists I update the needed columns to the database.
My problem is that sometimes when I update a row I get the "Row not found or changed" exception and yes I know it is because the row has been modified since I read it.
To solve this I have tried using the following without success:
Use using around my datacontext.
Use using around a TransactionScope.
Use a mutex, this doesn’t work because the web service is (not sure I am calling it the right think) replicated out on different PC for performance but still using the same database.
Resolve concurrency conflict in the exception, this doesn’t work because I need to get the new database value and add a value to it.
Below I have added the code used to log the statistics data. Any help would be appreciated very much.
public class StatisticsGateway : IStatisticsGateway
{
#region member variables
private StatisticsDataContext db;
#endregion
#region Singleton
[ThreadStatic]
private static IStatisticsGateway instance;
[ThreadStatic]
private static DateTime lastEntryTime = DateTime.MinValue;
public static IStatisticsGateway Instance
{
get
{
if (!lastEntryTime.Equals(OperationState.EntryTime) || instance == null)
{
instance = new StatisticsGateway();
lastEntryTime = OperationState.EntryTime;
}
return instance;
}
}
#endregion
#region constructor / initialize
private StatisticsGateway()
{
var configurationAppSettings = new System.Configuration.AppSettingsReader();
var connectionString = ((string)(configurationAppSettings.GetValue("sqlConnection1.ConnectionString", typeof(string))));
db = new StatisticsDataContext(connectionString);
}
#endregion
#region IStatisticsGateway members
public void AddStatisticRecord(StatisticRecord record)
{
using (db)
{
var existing = db.Statistics.SingleOrDefault(p => p.MethodName == record.MethodName &&
p.CountryID == record.CountryID &&
p.TokenType == record.TokenType &&
p.Year == record.Year &&
p.Month == record.Month);
if (existing == null)
{
//Add new row
this.AddNewRecord(record);
return;
}
//Update
existing.Count += record.Count;
existing.TotalTimeValue += record.TotalTimeValue;
db.SubmitChanges();
}
}
I would suggest letting SQL Server deal with the concurrency.
Here's how:
Create a stored procedure that accepts your log values (method name, month/date, and execution statistics) as arguments.
In the stored procedure, before anything else, get an application lock as described here, and here. Now you can be sure only one instance of the stored procedure will be running at once. (Disclaimer! I have not tried sp_getapplock myself. Just saying. But it seems fairly straightforward, given all the examples out there on the interwebs.)
Next, in the stored procedure, query the log table for a current-month's entry for the method to determine whether to insert or update, and then do the insert or update.
As you may know, in VS you can drag stored procedures from the Server Explorer into the DBML designer for easy access with LINQ to SQL.
If you're trying to avoid stored procedures then this solution obviously won't be for you, but it's how I'd solve it easily and quickly. Hope it helps!
If you don't want to use the stored procedure approach, a crude way of dealing with it would simply be retrying on that specific exception. E.g:
int maxRetryCount = 5;
for (int i = 0; i < maxRetryCount; i++)
{
try
{
QueryAndUpdateDB();
break;
}
catch(RowUpdateException ex)
{
if (i == maxRetryCount) throw;
}
}
I have not used the sp_getapplock, instead I have used HOLDLOCK and ROWLOCK as seen below:
CREATE PROCEDURE [dbo].[UpdateStatistics]
#MethodName as varchar(50) = null,
#CountryID as varchar(2) = null,
#TokenType as varchar(5) = null,
#Year as int,
#Month as int,
#Count bigint,
#TotalTimeValue bigint
AS
BEGIN
SET NOCOUNT ON;
BEGIN TRAN
UPDATE dbo.[Statistics]
WITH (HOLDLOCK, ROWLOCK)
SET Count = Count + #Count
WHERE MethodName=#MethodName and CountryID=#CountryID and TokenType=#TokenType and Year=#Year and Month=#Month
IF ##ROWCOUNT=0
INSERT INTO dbo.[Statistics] (MethodName, CountryID, TokenType, TotalTimeValue, Year, Month, Count) values (#MethodName, #CountryID, #TokenType, #TotalTimeValue, #Year, #Month, #Count)
COMMIT TRAN
END
GO
I have tested it by calling my web service methods by multiple threads simultaneous and each call is logged without any problems.