i am facing some problems in my project. when i try to update entity it gives me different type of errors.
i read from net. these errors are because
1 - I am getting Object of entity class from method which creates DataContext locally
and in update method id does not update because here another DataContext is created locally.
(even it does not throw any exception)
i found many articles related to this problem
1 - Adding timestamp column in table (does not effect in my project. i tried this)
one guy said that use SINGLE DataContext for everyone.
i did this by creating the following class
public class Factory
{
private static LinqDemoDbDataContext db = null;
public static LinqDemoDbDataContext DB
{
get
{
if (db == null)
db = new LinqDemoDbDataContext();
return db;
}
}
}
public static Student GetStudent(long id)
{
LinqDemoDbDataContext db = Factory.DB;
//LinqDemoDbDataContext db = new LinqDemoDbDataContext();
Student std = (from s in db.Students
where s.ID == id
select s).Single();
return std;
}
public static void UpdateStudent(long studentId, string name, string address)
{
Student std = GetStudent(studentId);
LinqDemoDbDataContext db = Factory.DB;
std.Name = name;
std.Address = address;
db.SubmitChanges();
}
in this case i want to update student details.
it solved my problem. but now the question is.
Is it good approach to use above technique in Web Based application???
Is it good approach to use above technique in Web Based application???
No. DataContext is not thread safe. You cannot share 1 DataContext among the different threads handling different requests safely.
Also - this pattern is called Singleton, not Factory
Related
I am creating a Web API. I need to fetch ~50 table data in a single request for some calculations. Since I am fetching these many tables together my Web API response time is high. All the tables are independent. I am using repository pattern and EF code first approach. Any suggestions to improve the response time for the given scenario :
The code looks like below :
public static class FetchDataExtensions
{
public static DbData GetData(this IRepository repo, Request request)
{
return new DbData
{
// fetching data from db using repository pattern
Table1 = repo.GetTable1Data(request.name, request.gender),
Table2 = repo.GetTable2Data(request.gender),
Table3 = repo.GetTable3Data(),
........
Table50 = repo.GetTable50Data()
};
}
}
Repository.cs
public class Repository : IRepository
{
private readonly DBContext context;
public Repository(DBContext context)
{
this.context = context;
}
public Table1 GetTable1Data(string name, string gender)
{
try
{
return context.Table1.Single(a => a.Name.Equals(name.ToString(), StringComparison.OrdinalIgnoreCase)
&& a.Gender.Equals(gender.ToString(), StringComparison.OrdinalIgnoreCase));
}
catch (Exception ex)
{}
}
}
You can use async-await threading concept. Where at a time multiple tread will read data and it will help you to minimize table reading time.
for refer [example of async-await][1]
[1]: https://www.tutorialspoint.com/entity_framework/entity_framework_asynchronous_query.htm
a part from that you can using indexing. See how to apply indexing on table in EF.
My application can connect with multiple data bases (every data base have the same schema), I store the current DB, selected by user, in Session and encapsule access using a static property like:
public class DataBase
{
public static string CurrentDB
{
get
{
return HttpContext.Current.Session["CurrentDB"].ToString();
}
set
{
HttpContext.Current.Session["CurrentDB"] = value;
}
}
}
Other pieces of code access the static CurrentDB to determine what DB use.
Some actions start background process in a thread and it need access the CurrentDB to do some stuff. I'm thinking using something like this:
[ThreadStatic]
private static string _threadSafeCurrentDB;
public static string CurrentDB
{
get
{
if (HttpContext.Current == null)
return _threadSafeCurrentDB;
return HttpContext.Current.Session["CurrentDB"].ToString();
}
set
{
if (HttpContext.Current == null)
_threadSafeCurrentDB = value;
else
HttpContext.Current.Session["CurrentDB"] = value;
}
}
And start thread like:
public class MyThread
{
private string _currentDB;
private thread _thread;
public MyThread (string currentDB)
{
_currentDB = currentDB;
_thread = new Thread(DoWork);
}
public DoWork ()
{
DataBase.CurrentDB = _currentDB;
... //Do the work
}
}
This is a bad practice?
Actually, I think you should be able to determine which thread uses which database, so I would create a class inherited from Thread, but aware of the database it uses. It should have a getDB() method, so, if you need a new Thread which will use the same database as used in another specific Thread, you can use it. You should be able to setDB(db) of a Thread as well.
In the session you are using a current DB approach, which assumes that there is a single current DB. If this assumption describes the truth, then you can leave it as it is and update it whenever a new current DB is being used. If you have to use several databases in the same time, then you might want to have a Dictionary of databases, where the Value would be the DB and the Key would be some kind of code which would have a sematic meaning which you could use to be able to determine which instance is needed where.
I'm still new to LINQ and am having some issues in knowing where to put a DataContext in a Class.
Here's what I've tried:
public class Student
{
private static LinqClassesDataContext db = new LinqClassesDataContext();
public static Profile GetProfile(int uID)
{
var profile = (from p in db.Profiles
where p.uID == uID
select p).FirstOrDefault();
return profile;
}
}
But I'm having issues of the result caching(?) - see this issue: Weird caching issue with ASP.net/Linq
Then, I tried putting the DataContext in each of the methods in the class:
public class Student
{
public static Profile GetProfile(int uID)
{
using (LinqClassesDataContext db = new LinqClassesDataContext())
{
var profile = (from p in db.Profiles
where p.uID == uID
select p).FirstOrDefault();
return profile;
}
}
}
But then I was getting a “DataContext accessed after Dispose” error in my application.
So, the only other way that I've seen this done is this way:
public class Student
{
public static Profile GetProfile(int uID)
{
LinqClassesDataContext db = new LinqClassesDataContext();
{
var profile = (from p in db.Profiles
where p.uID == uID
select p).FirstOrDefault();
return profile;
}
}
}
But it seems that this isn't the most efficient way. Perhaps I'm using Linq incorrectly (I'm a self taught ASP.net'er), but can someone enlighten me on what the best way to move forward?
Objects are attached to the context, so as soon as you dispose it, if you try to navigate it's relationships, you will get these kinds of errors as you got with option #2.
Since ASP.NET is stateless, you need to either load the profile object every time it's needed, and not cache the object statically, or load the object and all of it's related data using the DataLoadOptions object of LINQ to SQL (see this). That way, you shouldn't need the context when accessing related data sets.
As far as where to put it, I always put it in HttpContext.Current.Items collection, which can store the instance per request, and then share it from here across all requests. I wrap some code around it so my application doesn't know that it's getting it from here. However, you have to be careful, because if a process outside of ASP.NET uses the same code, this approach blows up because there is no HTTP context. In that case, instantiate the context every time.
I have an ASP.NET website project that until recent had all code in App_Code folder. It uses Entity Framework 4 as ORM. Application is divided into three "sections" (let's say one for each customer). Each section has it's own database (but same schema). This is due to performance reasons, databases are over 10GB each with millions of rows.
Each time a context object is created a Session variable which holds section ID is called and proprietary connection string is chosen for this context.
It looks like this (following are members of static Connection class):
public static MyEntities GetEntityContext()
{
if (HttpContext.Current.Session["section"] == null)
{
HttpContext.Current.Response.Redirect("~/Login.aspx");
}
var context = new MyEntities(GetEntityConnectionStringForSection((int)HttpContext.Current.Session["section"]);
return context;
}
private static string GetEntityConnectionStringForSection(int section)
{
switch (section)
{
case 1: return ConfigurationManager.ConnectionStrings["entity_1"].ConnectionString;
case 2: return ConfigurationManager.ConnectionStrings["entity_2"].ConnectionString;
case 3: return ConfigurationManager.ConnectionStrings["entity_3"].ConnectionString;
default: return ConfigurationManager.ConnectionStrings["entity_1"].ConnectionString;
}
}
It works very good and also handles situation when session timed out everytime any data access is performed.
Recently as I needed to share DB classes among two websites I moved all DB classes to separate class library and referenced System.Web library which I know is bad practice, but it's working.
Now the next step is to include unit and module tests which as I read is very difficult or impossible when using HttpContext in library, so I want to get rid of System.Web references. What is the best practice for this situation?
I think I can't just pass HttpContext to GetEntityContext() as it is also called from within my entity classes. Although this probably can be refactored. So maybe this is where I should go?
I also wondered if is it possible to somehow pass current section ID to this whole library? It cannot be just static property because as far as I understand it would be common for all users using the application. This should be user-specific.
Reassuming the objective is to make automated testing possible without loosing transparent Connection String choosing and session timeouts handling.
If I do something fundamentally wrong at this stage please also let me know. I can look again at this question tomorrow morning (8.00 am UTC) so please don't be discouraged by my silence till then.
EDIT:
Example of usage of Connection class in the library:
public partial class Store
{
public static List<Store> GetSpecialStores()
{
using (var context = Connection.GetEntityContext())
{
return context.Stores.Where(qq => qq.Type > 0).OrderBy(qq => qq.Code).ToList();
}
}
}
You can declare interface IContextProvider inside your library ans use it to retrieve context. Something like:
public interface IContextProvider
{
MyEntities GetEntityContext();
}
This will make your library testable. In your web project you can inject IContextProvider implementation into your library.
public class WebContextProvider : IContextProvider
{
public MyEntities GetEntityContext()
{
if (HttpContext.Current.Session["section"] == null)
HttpContext.Current.Response.Redirect("~/Login.aspx");
int sectionId = (int)HttpContext.Current.Session["section"];
string connectionString = GetEntityConnectionStringForSection(sectionId);
var context = new MyEntities(connectionString);
return context;
}
private static string GetEntityConnectionStringForSection(int section)
{
switch (section)
{
case 1: return ConfigurationManager.ConnectionStrings["entity_1"].ConnectionString;
case 2: return ConfigurationManager.ConnectionStrings["entity_2"].ConnectionString;
case 3: return ConfigurationManager.ConnectionStrings["entity_3"].ConnectionString;
default: return ConfigurationManager.ConnectionStrings["entity_1"].ConnectionString;
}
}
}
Inject this interface to repositories or other data access classes.
public partial class Store
{
private IContextProvider contextProvider;
public Store(IContextProvider contextProvider)
{
this.contextProvider = contextProvider;
}
public List<Store> GetSpecialStores()
{
using (var context = contextProvider.GetEntityContext())
{
return context.Stores.Where(qq => qq.Type > 0).OrderBy(qq => qq.Code).ToList();
}
}
}
I hope this makes sense. I have a ASP.NET web application that uses Entity Framework. I have added a couple of custom tables to the db and created a separate project to handle the CRUD operations for those tables. I chose the separate project because I don't want future upgrades to the application to overwrite my custom features.
My problem is this. How do I attach/combine my custom ObjectContext to the ObjectContext of the application? I want to use the same UnitOfWorkScope (already in the application) to maintain the one ObjectContext instance per HTTP request. Again, I don't want to add my ObjectSets to the application's ObjectContext for my reason listed above.
Here is some code:
Widget.cs
public partial class Widget
{
public Widget()
{
}
public int WidgetId {get;set;}
public string WidgetName {get;set;}
}
WidgetObjectContext.cs
public partial class WidgetObjectContext : ObjectContext
{
private readonly Dictionary<Type, object> _entitySets;
public ObjectSet<T> EntitySet<T>()
where T : BaseEntity
{
var t = typeof(T);
object match;
if(!_entitySets.TryGetValue(t, out match))
{
match = CreateObjectSet<T>();
_entitySets.Add(t, match);
}
return (ObjectSet<T>)match;
}
public ObjectSet<Widget> Widgets
{
get
{
if((_widgets == null))
{
_widgets = CreateObjectSet<Widget>();
}
return _widget;
}
}
private ObjectSet<Widget> _widgets;
In my WidgetManager class if I was using the application's ObjectContext I would query my tables like this:
var context = ObjectContextHelper.CurrentObjectContext;
var query = from c in context.ObjectSet .... etc
What I want would be to do something like this:
var context = ObjectContextHelper.CurrentObjectContext.Attach(WidgetObjectContext);
I know this won't work but that is the gist of what I am trying to accomplish. Hope this is clear enough. Thanks.
I don't think it is possible. ObjectContext creates entity connection which connects to metadata describing mapping and database. But you have to different sets of metadata - one for ASP.NET application and one for separate project. Simply you need two connection to work with these models => you need two ObjectContexts.
FYI: The previous answer was correct at the time of the answer. It is now possible to do this using the DbContext available in EF 4.1. The caveat is that you must use the code-first strategy in order to build your custom context. In other words, you won't be able to use EDMX files to accomplish this.