In this system one program creates table records and a second updates them. I want the update program to see the new records. See lots of queries/responses to this but so far none have worked for me. One solution was to clear and reload the dataset table. The following code recreates the dataset but I can't include the auto incremented primary key bookid. If it is there I get an overload error even thought the field count is correct. If I remove it the dataset.booking table is loaded but the bookid values are wrong negative numbers) and I can't update the dataset.booking table as it does not match the database table.
tclDataSet3.booking.AcceptChanges();
tclDataSet3.booking.Clear();
bookingBindingSource.ResetBindings(false);
dataGridView1.ClearSelection();
var bkas1 = tcdb.bookings.Where(b => b.approvalStatus == 1);
foreach (booking bk in bkas1)
tclDataSet3.booking.AddbookingRow(
(int)bk.bookId,
(int)bk.bookYear,
(int)bk.bookMonth,
(int)bk.bookDay,
(int)bk.workOrder,
(int)bk.customerNum,
bk.firstName,
bk.lastName,
bk.vehicle,
(int)bk.serviceCar,
bk.repairType,
(bool)bk.isCompleted,
(bool)bk.isPickedUp,
bk.outYear,
bk.outMonth,
bk.outDay,
(bool)bk.isDeleted,
(int)bk.isUpdated,
bk.bookingTime,
(int)bk.approvalStatus);
Program requirements:
display datagridview of dataset.booking table where as_code = 1
updates rows in datagrideview to change as_code = 2
remove updated rows from datagridview (bookingBindingSource.RemoveCurrent(); works well)
Refresh datagridview to see all dataset.booking table rows where as_code = 1
Currently the refresh only sees existing records in the datagrideview.
Is there a better way to do this?
After much trial and error I decided to rewrite the code to manually build the dataGridView rather than use any data binding. I created a subroutine to clear the dataGridView, read the base table and rebuild the dataGridView.
I had a complex view joining a couple of tables but it freezed my C# app so I simplified it in order to get it to work, however it still freezes and I dont have a clue why.
I have a table called 'admittances' containing: AdmittanceID, Number, Date, Notes.
I created a view which selects three of those: AdmittanceID as ID, Number as Number and Date as Date.
In a database it just works, no big deal. I mapped it via 'Update model from database' option in a model wizard inside C# EF model and it shows up as an entity with three columns and entity key column 'ID'.
However while trying to loop over all the records the program stops working and does not go any further (in debugging it just does not pass through the loop).
meraserwEntities db = new meraserwEntities();
var myQuery = db.clientstodevices.ToList();
//Tried also other versions that are listed below
var myQuery = from d in db.clientstodevices select d;
foreach (var item in myQuery)
{
ClientsToDevices.Add(item);
}
// Or without loop - then it freezed exactly in this line
ClientsToDevices = db.clientstodevices.ToList();
Please help, tried everything ..
In EF Core you can "reload" an Entity from the data store to pickup any changes.
An example of why you might need to do that is if you need to resolve a DB concurrency exception on SaveChanges.
This does work ok for one record...
EntityEntry<T> entityEntry = GetEntity(123);
entityEntry.Reload();
The only problem is, the Reload() executes a SQL statement per entityEntry.
So, if you want to refresh a set of entityEntry, you get a SQL statement per entry.
Whereas, the normal context.Set<T>().Load(); executes one SQL statement that retrieves all of the rows.
With a small number of entityEntry, the performance hit is negligable; but anytime I see a RBAR design approach, it raises a red flag for me.
Question: other than a RBAR loop
foreach (var e in context.ChangeTracker.Entries<T>)
{
e.Reload();
}
is there a way to re-execute the context.Set<T>().Load(); to reload the entries as a set?
Note: I am using the
context.Entry(e).State = EntityState.Detached
approach now; checking to see if there is something better that I have missed.
UPDATE 1
How I am testing
Read data from database
Add record to database
Delete record from database
Change record in database
"reload" data
the result I am looking to get is
entity for changed record is updated
entity for deleted record is removed
"optionally" entity for new record is added
the Add is optional because that is not the designed behaviour of "reload", which is to update existing entity.
I can't believe it is so hard to get someone to show me a simple working example. It leads me to believe that everyone can only talk like they know how to do it but in reality they don't.
I shorten the post down to only what I want the example to do. Maybe the post was getting to long and scared people away.
To get this bounty I am looking for a WORKING EXAMPLE that I can copy in VS 2010 and run.
What the example needs to do.
Show what datatype should be in my domain for version as a timestamp in mssql 2008
Show nhibernate automatically throwing the "StaleObjectException"
Show me working examples of these 3 scenarios
Scenario 1
User A comes to the site and edits Row1. User B comes(note he can see Row1) and clicks to edit Row1, UserB should be denied from editing the row until User A is finished.
Scenario 2
User A comes to the site and edits Row1. User B comes 30mins later and clicks to edit Row1. User B should be able to edit this row and save. This is because User A took too long to edit the row and lost his right to edit.
Scenario 3
User A comes back from being away. He clicks the update row button and he should be greeted with StaleObjectException.
I am using asp.net mvc and fluent nhibernate. Looking for the example to be done in these.
What I tried
I tried to build my own but I can't get it throw the StaleObjectException nor can I get the version number to increment. I tired opening 2 separate browser and loaded up the index page. Both browsers showed the same version number.
public class Default1Controller : Controller
{
//
// GET: /Default1/
public ActionResult Index()
{
var sessionFactory = CreateSessionFactory();
using (var session = sessionFactory.OpenSession())
{
using (var transaction = session.BeginTransaction())
{
var firstRecord = session.Query<TableA>().FirstOrDefault();
transaction.Commit();
return View(firstRecord);
}
}
}
public ActionResult Save()
{
var sessionFactory = CreateSessionFactory();
using (var session = sessionFactory.OpenSession())
{
using (var transaction = session.BeginTransaction())
{
var firstRecord = session.Query<TableA>().FirstOrDefault();
firstRecord.Name = "test2";
transaction.Commit();
return View();
}
}
}
private static ISessionFactory CreateSessionFactory()
{
return Fluently.Configure()
.Database(MsSqlConfiguration.MsSql2008
.ConnectionString(c => c.FromConnectionStringWithKey("Test")))
.Mappings(m => m.FluentMappings.AddFromAssemblyOf<TableA>())
// .ExposeConfiguration(BuidSchema)
.BuildSessionFactory();
}
private static void BuidSchema(NHibernate.Cfg.Configuration config)
{
new NHibernate.Tool.hbm2ddl.SchemaExport(config).Create(false, true);
}
}
public class TableA
{
public virtual Guid Id { get; set; }
public virtual string Name { get; set; }
// Not sure what data type this should be for timestamp.
// To eliminate changing to much started with int version
// but want in the end timestamp.
public virtual int Version { get; set; }
}
public class TableAMapping : ClassMap<TableA>
{
public TableAMapping()
{
Id(x => x.Id);
Map(x => x.Name);
Version(x => x.Version);
}
}
Will nhibernate stop the row from being retrieved?
No. Locks are only placed for the extent of a transaction, which in a web application ends when the request ends. Also, the default type of transaction isolation mode is Read committed which means that read locks are released as soon as the select statement terminates. If you are reading and making edits in the same request and transaction, you could place a read and write lock on the row at hand which would prevent other transactions from writing to or reading from that row. However, this type of concurrency control doesn't work well in a web application.
Or would the User B be able to still see the row but if he tried to save it would crash?
This would happen if [optimistic concurrency] was being used. In NHibernate, optimistic concurrency works by adding a version field. Save/update commands are issued with the version upon which the update was based. If that differs from the version in the database table, no rows are updated and NHibernate will throw.
What happens if User A say cancels and does not edit. Do I have to
release the lock myself or is there a timeout can be set to release
the lock?
No, the lock is released at the end of the request.
Overall, your best bet is to opt for optimistic concurrency with version fields managed by NHibernate.
How does it look in code? Do I setup in my fluent nhibernate to
generate a timestamp(not sure if I would timespan datatype).
I would suggest using a version column. If you're using FluentNhibernate with auto mappings, then if you make a column called Version of type int/long it will use that to version by default, alternatively you can use the Version() method in the mapping to do so (it's similar for timestamp).
So now I generated somehow the timestamp and the user is editing a
row(through a gui). Should I be storing the timestamp in memory or
something? Then when the user submits call from memory the timestamp
and id of the row and check?
When the user starts editing a row, you retrieve it and store the current version (the value of the version property). I would recommend putting the current version in a hidden field in the form. When the user saves his changes, you can either do a manual check against the version in the database (check that it's the same as the version in the hidden field), or you can set the version property to the value from the hidden field (if you are using databinding, you could do this automatically). If you set the version property, then when you try to save the entity, NHibernate will check that the version you're saving matches the version in the database, and throws an exception if it doesn't.
NHibernate will issue an update query something like:
UPDATE xyz
SET ,
Version = 16
WHERE Id = 1234 AND Version = 15
(assuming your version was 15) - in the process it will also increment the version field
If so that means the business logic is keeping track of the "row
locking" but in theory someone still could just go Where(x => x.Id ==
id) and grab that row and update at will.
If someone else updates the row via NHibernate, it will increment the version automatically, so when your user tries to save it with the wrong version you will get an exception which you need to decide how to handle (ie. try show some merge screen, or tell the user to try again with the new data)
What happens when the row gets updated? Do you set null to the timestamp?
It updates the version or timestamp (timestamp will get updated to the current time) automatically
What happens if the user never actually finishes updating and leaves. How does the row
every become unlocked again?
The row is not locked per se, it is instead using optimistic concurrency, where you assume that no-one will change the same row at the same time, and if someone does, then you need to retry the update.
Is there still a race condition what happens or is this next to
impossible in happening? I am just concerned 2 ppl try to get edit the
same row and both of them see it in their gui for editing but one is
actually going to get denied in the end because they lost the race
condition.
If 2 people try to edit the same row at the same time, one of them will lose if you're using optimistic concurrency. The benefit is that they will KNOW that there was a conflict, as opposed to either losing their changes and thinking that it updated, or overwriting someone else's changes without knowing about it.
So I did something like this
var test = session.Query.Where(x => x.Id ==
id).FirstOrDefault(); // send to user for editing. Has versioning on
it. user edits and send back the data 30mins later.
Codes does
test.Id = vm.Id; test.ColumnA = vm.ColumnA; test.Version = vm.Version;
session.Update(test); session.Commit(); So the above will work right?
The above will throw an exception if someone else has gone in and changed the row. That's the point of it, so you know that a concurrency issue has arisen. Typically you'd show the user a message saying "Someone else has changed this row" with the new row there and possibly their changes also so the user has to select which changes win.
but if I do this
test.Id = vm.Id;
test.ColumnA = vm.ColumnA;
session.Update(test);
session.Commit(); it would not commit right?
Correct as long as you haven't reloaded test (ie. you did test = new Xyz(), not test = session.Load() ) because the Timestamp on the row wouldn't match
If someone else updates the row via NHibernate, it will increment the
version automatically, so when your user tries to save it with the
wrong version you will get an exception which you need to decide how
to handle (ie. try show some merge screen, or tell the user to try
again with the new data)
Can I make it so when the record is grabbed this checked. I want to
keep it simple at first that only one person can edit at a time. The
other guy won't even be able to access the record to edit while
something is editing it.
That's not optimistic concurrency. As a simple answer you could add a CheckOutDate property which you set when someone starts editing it, and set it to null when they finish. Then when they start to edit, or when you show them the rows to edit you could exclude all rows where that CheckOutDate is newer than say the last 10 minutes (then you wouldn't need a scheduled task to reset it periodically)
The row is not locked per se, it is instead using optimistic
concurrency, where you assume that no-one will change the same row at
the same time, and if someone does, then you need to retry the update.
I am not sure what your saying does this mean I can do
session.query.Where(x => x.id == id).FirstOrDefault(); all day
long and it will keep getting me the record(thought it would keep
incrementing the version).
The query will NOT increment the version, only an update to it will increment the version.
I don't know that much about nHibernate itself, but if you are prepared to create some stored procs on the database it can >sort of< be done.
You will need one extra data column and two fields in your object model to store information against each row:
A 'hash' of all the field values (using SQL Server CHECKSUM 2008 and later or HASHBYTES for earlier editions) other than the hash field itself and the EditTimestamp field. This could be persisted to the table using INSERT/UPDATE triggers if needs be.
An 'edit-timestamp' of type datetime.
Change your procedures to do the following:
The 'select' procedure should include a where clause similar to 'edit-timestamp < (Now - 30 minutes)' and should update the 'edit-timestamp' to the current time. Run the select with appropriate locking BEFORE updating the row I'm thinking a stored procedure with hold locking such as this one here Use a persistent date/time rather than something like GETDATE().
Example (using fixed values):
BEGIN TRAN
DECLARE #now DATETIME
SET #now = '2012-09-28 14:00:00'
SELECT *, #now AS NewEditTimestamp, CHECKSUM(ID, [Description]) AS RowChecksum
FROM TestLocks
WITH (HOLDLOCK, ROWLOCK)
WHERE ID = 3 AND EditTimestamp < DATEADD(mi, -30, #now)
/* Do all your stuff here while the record is locked */
UPDATE TestLocks
SET EditTimestamp = #now
WHERE ID = 3 AND EditTimestamp < DATEADD(mi, -30, #now)
COMMIT TRAN
If you get a row back from this procedure then you 'have' the 'lock', otherwise, no rows will be returned and there's nothing to edit.
The 'update' procedure should add a where clause similar to 'hash = previously returned hash'
Example (using fixed values):
BEGIN TRAN
DECLARE #RowChecksum INT
SET #RowChecksum = -845335138
UPDATE TestLocks
SET [Description] = 'New Description'
WHERE ID = 3 AND CHECKSUM(ID, [Description]) = #RowChecksum
SELECT ##ROWCOUNT AS RowsUpdated
COMMIT TRAN
So in your scenarios:
User A edits a row. When you return this record from the database, the 'edit-timestamp' has been updated to the current time and you have a row so you know you can edit. User B would not get a row because the timestamp is still too recent.
User B edits the row after 30 minutes. They get a row back because the timestamp has passed more than 30 minutes ago. The hash of the fields will be the same as for user A 30 minutes ago as no updates have been written.
Now user B updates. The previously retrieved hash still matches the hash of the fields in the row, so the update statement succeeds, and we return the row-count to show that the row was updated. User A however, tries to update next. Because the value of the description field has changed, the hashvalue has changed, and so nothing is updated by the UPDATE statement. We get a result of 'zero rows updated' so we know that either the row has since been changed or the row was deleted.
There are probably some issues regarding scalability with all these locks going on and the above code could be optimised (might get problems with clocks going forward/back for example, use UTC), but I wrote these examples just to explain how it could work.
Outside of that I can't see how you can do this without utilising database level row-locking within the select transaction. It might be that you can request those locks via nHibernate, but that's beyond my knowledge of nHibernate I'm afraid.
Have you looked at the ISaveOrUpdateEventListener interface?
public class SaveListener : NHibernate.Event.ISaveOrUpdateEventListener
{
public void OnSaveOrUpdate(NHibernate.Event.SaveOrUpdateEvent e)
{
NHibernate.Persister.Entity.IEntityPersister p = e.Session.GetEntityPersister(null, e.Entity);
if (p.IsVersioned)
{
//TODO: check types etc...
MyEntity m = (MyEntity) e.Entity;
DateTime oldversion = (DateTime) p.GetVersion(m, e.Session.EntityMode);
DateTime currversion = (DateTime) p.GetCurrentVersion(m.ID, e.Session);
if (oldversion < currversion.AddMinutes(-30))
throw new StaleObjectStateException("MyEntity", m.ID);
}
}
}
Then in your Configuration, register it.
private static void Configure(NHibernate.Cfg.Configuration cfg)
{
cfg.EventListeners.SaveOrUpdateEventListeners = new NHibernate.Event.ISaveOrUpdateEventListener[] {new SaveListener()};
}
public static ISessionFactory CreateSessionFactory()
{
return Fluently.Configure().Database(...).
.Mappings(...)
.ExposeConfiguration(Configure)
.BuildSessionFactory();
}
And version the Properties you want to version in your Mapping class.
public class MyEntityMap: ClassMap<MyENtity>
{
public MyEntityMap()
{
Table("MyTable");
Id(x => x.ID);
Version(x => x.Timestamp);
Map(x => x.PropA);
Map(x => x.PropB);
}
}
The short answer to your question is you can't/shouldn't do this in a simple web application with nhibernates optimistic (version) and pessimistic (row locks) locking. The fact that your transactions are only as long as a request are your limiting factor.
What you CAN do is create another table and entity class, and mappings that manages these "locks". At the lowest level you need an Id of the object being edited and the Id of the user performing the editing, and a datetime of when the lock was acquired. I would make the Id of the object being edited the primary key since you want it to be exclusive...
When a user clicks on a row to edit, you can try to acquire a lock (create a new record in that table with the ids and current datetime). If the lock already exists for another user, than it will fail because you are trying to violate a primary key constraint.
If a lock is acquired, when the user clicks save you need to check that they still have a valid "lock" before performing the actual save. Then, perform the actual save and remove the lock record.
I would also recommend a background service/process that sweeps these locks periodically and removes the ones that have expired or are older than your time limit.
This is my prescribed way of dealing with "locks" in a web environment. Good luck!
Yes, it is possible to lock a row with nhibernate but if I understand well, your scenario is in a web context and then it is not the best practice.
The best practive is to use optimistic locking with automatic versioning as you mentioned.
Locking a row when page is opening and releasing it when page is unloading will quickly lead to dead lock the row (javascript issue, page not killed properly...).
Optimistic locking will make NHibernate throws an exception when flushing a transaction which contains objects modified by another session.
If you want to have true concurent modification of the same information you may try to think about a system which merge many users input inside a same document, but it is a system on its own, not managed by ORM.
You will have to choose a way to deal with session in a web environment.
http://nhibernate.info/doc/nh/en/index.html#transactions-optimistic
The only approach that is consistent with high concurrency and high
scalability is optimistic concurrency control with versioning.
NHibernate provides for three possible approaches to writing
application code that uses optimistic concurrency.
Hey you can try these sites
http://thesenilecoder.blogspot.ca/2012/02/nhibernate-samples-row-versioning-with.html
http://stackingcode.com/blog/2010/12/09/optimistic-concurrency-and-nhibernate
I have a multi-page (multi-view) form in MVC, the results of which will be saved to a single database table.
Code snippet that initializes the linq object in the first page of the form.
public ActionResult MyForm()
{
// returns a Linq object stored in session
Application currentApp = Application.FromSession();
// if null, initialize the object and save to session
if (currentApp == null)
{
currentApp = new Application();
currentApp.SessionSave();
}
return View(currentApp);
}
And here is a sample snippet of code for the final action that updates some data from the strongly-typed model, then triggers the database save.
[HttpPost]
public ActionResult MyForm3(Application app, FormCollection coll)
{
Application currentApp = Application.FromSession();
currentApp.Contact = app.Contact;
currentApp.AddFormToXml(coll);
currentApp.SessionSave();
_db.Applications.InsertOnSubmit(currentApp);
_db.SubmitChanges();
return RedirectToAction("Blah");
}
The problem I'm running into is that the SubmitChanges fails with the error
Cannot insert the value NULL into
column 'ApplicationData', table
'MyTable';
column does not allow nulls. INSERT
fails. The statement has been
terminated.
In this case, ApplicationData is a column of type xml, which LINQ interprets as an XElement object. When I set a breakpoint at SubmitChanges() and check the value of app.ApplicationData, it is clearly populated (non-null), and yet I continue to get this error. My only thought is that I am misunderstanding something with how data contexts work. It only seems to have an issue with this one column though. Is it possible that I need to figure out a way to attach the XElement object (ApplicationData) to my active data context (_db), and if so, how would I go about doing that?
Take a look at the actual SQL generated and sent to the server.
Start up SQL Server Profiler (on the tools menu in SQL Server Management Studio) and start a trace. Run your application until it crashes. Go back to SQL profiler and look at the SQL queries. Seeing things from the SQL end sometimes make it easy to spot the error, e.g. finding out if your are doing several inserts instead of just one.
Well my suggestion to you is to compare the data type of "ApplicationData" column in your Context model and in your database table.
Also please check your LINQ to SQL mappings for this column "AppliationData" again on the datatype itself.
Please update your post if you find anything...
Ok, so in the action method you mentioned can you check if you are calling the InsertOnSumbit Method again anywhere else before you are finally calling db.SubmitChanges()...or if you are calling the InsertOnSubmit method more than once... I think that will cause a problem if you are calling it twice on the same object.
Update:
I did tried a sample with a single table and was able to insert the xml data as mentioned below.
DataClassesDataContext ctx = new DataClassesDataContext();
Application a1 = new Application();
XName n = "dfdsf";
a1.ApplicationData = new XElement(n);
ctx.Applications.InsertOnSubmit(a1);
ctx.SubmitChanges();
so, now the question will be what does your column data looks like??? if you can post the sample content of the application data then it will be helpful. Also how are you setting the ApplicationData property value?