I have a method named GetAll() in service class which returns entities from entity framework. The method is as follows:
public ActionResult List()
{
var tasklogs = _timeLogService.GetAll()
.Select(l=>{
l.StartTime.Value.AddHours(1);
return l;
});
return PartialView(tasklogs);
}
I want to show data in the view modified as per some logic, in this example, I add one hour to the original date.
The issue is, if I refresh the page, I see the hours increasing for each page refresh i.e GetAll() method returns the last modified value, all though its not the same in database, i.e. I don't save date modification in database but GetAll returns modified dates.
I read somewhere that for this to work I need to detach entities.
So, my question is, is there a better way to do it in service layer, as I have to do it in many places. The root causue of modifying date is I save dates in UTC in db, but when I display it in views, I convert it to local timezone in controller actions.
I hope I made it clear.
Thanks
As written in my comment, issue is resolved after I changed DbContext instance creation to per request.
Related
Good afternoon fellow developers,
I have come across a scenario where I found myself needing to retrieve the list of pending changes from my model and editing a specific property of those entries before sending them to my back-end.
These are new entities I created using the createEntry() method of the OData model v2. But, at the time of creation of said entities, I do not possess the value I need to add to them yet. This is the list of entities I retrieve by using the getPendingChanges() method on my model:
What I need to do is to loop through each of these newly created entities and set a specific property into them before actually sending them to my back-end with the submitChanges() method. Bare in mind that these are entry objects created by the createEntry() method and exist only in my front-end until I am able to submit them with success.
Any ideas that might point me in the right direction? I look forward to reading from you!
I was able to solve this issue in the following way:
var oPendingChanges = this.model.getPendingChanges();
var aPathsPendingChanges = $.map(oPendingChanges, function(value, index) { return [index];});
aPathsPendingChanges.forEach(sPath => oModel.setProperty("/" + sPath + "/PropertyX","valueFGO"));
The first two instructions retrieve the entire list of pendingChanges objects and then builds an array of paths to each individual entry. I then use that array of paths to loop through my list of pending changes and edit into the property I want in each iteration of the loop. Special thanks to the folks at answers.sap for the guidance!
I have an array of bytes in my model
public byte[] created_dt { get; set; }
It represents a timestamp value in the database.
In my view , I am referring it as #model.created_dt
but it is coming as system.byte[]
How to resolve this?
Try as this is just an example to achieve the functionality
#foreach(var a in model.created_dt){
<label>#a</label>
}
Judging by the behavior, this looks like ASP.NET and you are simply seeing the output of an implicit call to ToString() on the array (the default way of displaying anything that does not have a template defined). You will have to do something with the raw byte data and present it to the user.
Since you refer to "timestamp" and the property name might suggest a record creation time, you may want to write a helper method to translate this raw data to a DateTime which you could then format accordingly.
However, one of the following is most likely true:
It strikes me as odd that you are using raw binary to store what should otherwise be a datetime2 column. (Or it is a datetime in your database but you're doing something unorthodox to retrieve the value.)
Your property/column name of "created_dt" is a misnomer and it is really a timestamp (i.e. rowversion) column. In which case I don't think this is something a user would know what to do with, and it probably doesn't belong on the UI.
Note I am referring to one request, and not several requests and sessions.
I have several components that require Doctrine user object, some are located in layout, others are located in templates. Sometimes I need that Doctrine user object in action. Currently I have added a function to sfUser class that loads that object from database, which means every time I call that function I make a call to db. I'd like to know where to store this object so that I can access it without having to query db every time I need it. Again, we're talking about a single request, not several requests or something that would require session.
Can I save it in sfContext somehow? Any other places so that it can be available everywhere?
You can store it in your model's Table class, because tables are always accessed as singletones.
class sfGuardUserTable extends PluginsfGuardUserTable
{
protected $specialUser = null;
public function getSpecialUser()
{
if (null === $this->specialUser)
{
$this->specialUser = $this->findOneById(1);
}
return $this->specialUser;
}
}
Now, you can use this in actions and components like this:
$u = sfGuardUserTable::getInstance()->getSpecialUser();
And you will always end up with one query.
you can configure Doctrine cache so that the result of this specific request is always cached. What if so good about it is that if you use, say, the APC backend, you will have it cached across requests. You also get query caching as a bonus (this is not result caching, read the link I provided carefully)!
i am devloping a site using .net MVC
i have a data access layer which basically consists of static list objects that are created from data within my database.
The method that rebuilds this data first clears all the list objects. Once they are empty it then add the data. Here is an example of one of the lists im using. its a method which generates all the UK postcodes. there are about 50 methods similar to this in my application that return all sorts of information, such as towns, regions, members, emails etc.
public static List<PostCode> AllPostCodes = new List<PostCode>();
when the rebuild method is called it first clears the list.
ListPostCodes.AllPostCodes.Clear();
next it re-bulilds the data, by calling the GetAllPostCodes() method
/// <summary>
/// static method that returns all the UK postcodes
/// </summary>
public static void GetAllPostCodes()
{
using (fab_dataContextDataContext db = new fab_dataContextDataContext())
{
IQueryable AllPostcodeData = from data in db.PostCodeTables select data;
IDbCommand cmd = db.GetCommand(AllPostcodeData);
SqlDataAdapter adapter = new SqlDataAdapter();
adapter.SelectCommand = (SqlCommand)cmd;
DataSet dataSet = new DataSet();
cmd.Connection.Open();
adapter.FillSchema(dataSet, SchemaType.Source);
adapter.Fill(dataSet);
cmd.Connection.Close();
// crete the objects
foreach (DataRow row in dataSet.Tables[0].Rows)
{
PostCode postcode = new PostCode();
postcode.ID = Convert.ToInt32(row["PostcodeID"]);
postcode.Outcode = row["OutCode"].ToString();
postcode.Latitude = Convert.ToDouble(row["Latitude"]);
postcode.Longitude = Convert.ToDouble(row["Longitude"]);
postcode.TownID = Convert.ToInt32(row["TownID"]);
AllPostCodes.Add(postcode);
postcode = null;
}
}
}
The rebuild occurs every 1 hour. this ensures that every 1 hour the site will have fresh set of cached data.
the issue ive got is that occasionally if during a rebuild, the server will be hit by a request and an exception is thrown. The exception is "Index was outside the bounds of the array." it is due to when a list is being cleared.
ListPostCodes.AllPostCodes.Clear(); - // throws exception - although its not always in regard to this list.
Once this exception is thrown application dies, All users are affected. I have to restart the server to fix it.
i have 2 questions...
If i utilise caching instead of static objects would this help ?
Is there any way i can say "while the rebuild is taking place, wait for it to complete until accepting requests"
any help is most appricaiated ;)
truegilly
1 If i utilise caching instead of
static objects would this help ?
Yes, all the things you do are easier done by the caching functionality that is build into ASP.NET
Is there any way i can say "while the
rebuild is taking place, wait for it
to complete until accepting requests"
The common pattern goes like this:
You request data from the Data layer
If the Datlayer sees that there is data in the cache, then it serves the data from cache
If no data is in the cache the data is requested from the db and put into cache. After that it is served to the client
There are rules (CacheDependency and Timeout) when the cache is to be cleared.
The easiest solution would be you stick to this pattern: This way the first request would hit the database and other requests get served from the cache. You trigger the refresh by implementing an SQLCacheDependency
You have to make sure that your list is not modified by one thread while other threads are trying to use it. This would be a problem even if you used the ASP.NET cache since collections are just not thread-safe. One way you can do this is by using a SynchronizedCollection instead of a List. Then make sure to use code like the following when you access the collection:
lock (synchronizedCollection.SyncRoot) {
synchronizedCollection.Clear();
etc...
}
You will also have to use locking when you read the collection. If you are enumerating over it, you should probably make a copy before doing so as you don't want to lock for a long time. For example:
List<whatever> tempCollection;
lock (synchrnonizedCollection.SyncRoot) {
tempCollection = new List<whatever>(synchronizedCollection);
}
//use temp collection to access cached data
The other option would be to create a ThreadSafeList class that uses locking internally to make the list object itself thread-safe.
I agree with Tom, you will have to do synchronization to make this work. One thing that would improve the performance is not clearing the list until you actually receive the new values from the database:
// Modify your function to return a new list instead of filling the existing one.
public static List<PostCode> GetAllPostCodes()
{
List<PostCode> temp = new List<PostCode>();
...
return temp;
}
And when you rebuild the data:
List<PostCode> temp = GetAllPostCodes();
AllPostCodes = temp;
This makes sure that your cached list is still valid while GetAllPostCodes() is executing. It also has the advantage that you can use a read-only list which makes the synchronization a bit easier.
In your case you need to refresh the data every one hour.
1) IT should use cache with absolute expiration set to 1 hour, so it expires after every 1 hour. Check the Cache before using it, by doing a NULL check.If its NULL get the data from DB and populate the Cache.
2) With above approach the disadvantage is that data can be stale by 1 hour. So if u want most updated data at all times, use SQLCacheDependency (PUSH). so whenever there is a change in the select command u r using, cache will be refreshed from the database with updated data.
how can i automatically update my entity objects changed values and save them to db.
I hava an Action like that
public ActionResult Update()
{
User userToUpdate = new User();
TryUpdateModel<User>(userToUpdate,ValueProvider);
BaseRepository.Context.AttachTo("User",userToUpdate);
BaseRepository.Context.SaveChanges();
return Json("");
}
ValuProvider : has the items that come
from the client as post data.
The problem on this code is the code update all the values but i want to update only the changed values.
How can i find the changed values on my entity object.
You should check out the ObjectContext.ApplyPropertyChanges Method
it is suppose to do what your asking for...
msdn
Two options:
On the View you could know the values that were changed by using Javascript and then you could pass that information to your controller.
You could simply compare the previous values (which you already have since you populated a view) and check each value before updating the DB.
I prefer last option, since at this point you could also check for data validation.
This is really a problem for your data access code, not anything to do with your controller. Pick an ORM that handles this for you and forget about the problem.