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Linq to SQL - Can changes persist over different DataContext instances

If I retrieve an object from the database using Linq to SQL in one method using an instance of DataContext, which closes on exit of that method, can I edit the object in a different method and with a different DataContext and have the changes take effect in the database?
i.e. Would something like the below work?
public void Foo()
{
using (var db = new DataContext())
{
Bar a = this.GetBar();
if (a != null)
{
a.Property1 = true;
db.SubmitChanges();
}
}
}
private Bar GetBar(string val)
{
using (var db = new DataContext())
{
return db.FirstOrDefault(x => x.Property2 == val);
}
}

There should be some kind of Attach method
Something like:
public void Foo()
{
using (var db = new DataContext())
{
Bar a = this.GetBar();
if (a != null)
{
db.Bars.Attach(a);
a.Property1 = true;
db.SubmitChanges();
}
}
}

c# Entity Framework when should I use an new dbContext?

I was wondering for some time what is the proper way to make a new instance of an dbcontext? I got some problem with it because when I make up change in my database through SQL Server my context doesn't update the data. Let me explain how my website work.
We are doing an appointment website for our customer to take appointment obviously. we will hosting all database on our server. How it work is the application made up 2 connection:
first connection
this connection connect all the time to the same database let's call it master.
It'll redirect the user to the good database with the url code in it example:
www.example.com/foo
the server will check for the code where here is foo
So it'll lookup in the table to matchup the code and then take the good database name where it should redirect and it's here that my second connection come's up
Second connection
This one will make the connection to the correct database according to the data the master has return. From here all seems to work well except for the DBContext that actually never update because I don't instantiate it correctly and I don't have an large experience with it. Here's the code i did with my coworker:
using System;
using System.Data.EntityClient;
using System.Data.SqlClient;
using System.Linq;
using System.Threading;
using System.Web;
using System.Web.Routing;
using WebRV.Models.Entities;
namespace WebRV.RouteDb
{
public class DbConnection
{
private static DbConnection instance;
private Cliniciel_WebRV_Entities db;
private String connectionString;
private readonly Cliniciel_WebRV_MasterEntities masterDb = new Cliniciel_WebRV_MasterEntities();
private Int32 idCie;
private static readonly object myLock = new object();
private DbConnection() {
var context = new HttpContextWrapper(System.Web.HttpContext.Current);
var routeData = RouteTable.Routes.GetRouteData(context);
// Use RouteData directly:
String code = routeData.Values["code"].ToString();
//String code = Thread.CurrentContext. .RequestContext.RouteData.Values["code"].ToString();
var response = masterDb.SYS_tbCustDBLocation.Where(p => p.CustDBLocationCode == code).ToList();
if (response.Count == 1)
{
try
{
db = CreateConnection(response.FirstOrDefault());
idCie = (db.SYS_vwCie.Where(p => p.ClinicielWebName == code).FirstOrDefault()).IdCie;
}
catch (Exception e)
{
throw e;
}
}
else {
throw new FormatException();
}
}
private Cliniciel_WebRV_Entities CreateConnection(SYS_tbCustDBLocation data)
{
connectionString = *****
db = new Cliniciel_WebRV_Entities();
db.Database.Connection.ConnectionString = connectionString;
db.Database.Connection.Open();
return db;
}
private static void CreateInstance() {
instance = new DbConnection();
}
public static DbConnection GetInstance() {
lock (myLock)
{
if (instance == null)
{
CreateInstance();
}
}
return instance;
}
public String GetConnectionString()
{
return connectionString;
}
public Cliniciel_WebRV_Entities GetConnection()
{
return db;
}
public Int32 GetIdCie()
{
//hard code 1 but test
//return idCie;
return 1;
}
}
}
and here's an example of how I use it:
//[CompanyCodeFilter]
public class HomeController : AppointementController
{
//public static Cliniciel_WebRV_Entities entityDB = DbConnection.GetConnection();
public HomeController()
{
base.Refresh();
}
public JsonResult GetConsultationDescription(Int32 idService)
{
//base.Refresh();
entityDB.Set<SYS_vwService>().AsNoTracking();
var motifDescription = entityDB.SYS_vwService.Where(s => s.IDLang == cultureName && s.IdService == idService && s.IdCie == idCie).FirstOrDefault();
var base64 = Convert.ToBase64String(motifDescription.ServiceImage);
var imgSrc = String.Format("data:image/gif;base64,{0}", base64);
var imageDecode = imgSrc;
if (base64 == "AA==")
{
imageDecode = "";
}
var result = new { motifDescription, imageDecode };
return Json(result, JsonRequestBehavior.AllowGet);
}
}
Here base.refresh() call this:
using System;
using System.Linq;
using WebRV.Filters;
using WebRV.Localization;
using WebRV.Models.Entities;
using WebRV.RouteDb;
namespace WebRV.Controllers
{
//[CompanyCodeFilter]
public class AppointementController : BaseController
{
protected Cliniciel_WebRV_Entities entityDB;
protected Int32 idCie;
protected String cultureName;
//public AppointementController() {
// Refresh();
//}
//Permet de bien vérifier quel DB utilisé, quel idCie et quel cultureName.
protected void Refresh() {
entityDB = DbConnection.GetInstance().GetConnection();
idCie= DbConnection.GetInstance().GetIdCie();
cultureName = CultureLocalization.GetCulture();
//cultureName = "en-ca";
}
}
}
If someone can help me to instantiate the connection properly it'll be appreciate thank you

I think you need to better understand how the db context works.
It's a combination of many design patterns but at a basic level, it's essentially a unit of work that tracks changes to the objects that represent data. Because of this, it's not meant to be used as a connection that stays open all the time and you can just go back and forward, although you could use it like that to a certain extent.
From your code, it looks like you are using it in an ASP.NET MVC application. Because of the nature of the application, you can do one of two things:
You can create the db context whenever you need to use it, or
You can create the db context as a property of the controller
In the end, they somewhat amount to the same thing. I personally would recommend you create an instance of the context whenever you need to use it, making sure to dispose of it properly. You could then have a base controller class that exposes a CreateConnetion() method that creates an instance for your contexts, sort of like the Cliniciel_WebRV_Entities CreateConnection() method you already have, except that you don't need to open the connection explicitly and the connection string can be passed on as a constructor parameter if you add a partial class and implement one for the context. Something like this:
public partial class Cliniciel_WebRV_Entities
{
public Cliniciel_WebRV_Entities(string nameOrConnectionString):base(nameOrConnectionString)
{
}
}
You can then use it like this:
private Cliniciel_WebRV_Entities CreateConnection()
{
//Code to figure out which db to connect to (based on the other connection. You should consider caching that too if it doesn't change very often)
var nameOrConnectionString = FigureOutConnection();
var db = new Cliniciel_WebRV_Entities(nameOrConnectionString);
return db;
}
Keep in mind that the context depends on the metadata so make sure your connection string reflects that.
In your code, you would then consume it like this:
public JsonResult GetConsultationDescription(Int32 idService)
{
using(var entityDB = CreateConnection())
{
var motifDescription = entityDB.SYS_vwService.Where(s => s.IDLang == cultureName && s.IdService == idService && s.IdCie == idCie).FirstOrDefault();
var base64 = Convert.ToBase64String(motifDescription.ServiceImage);
var imgSrc = String.Format("data:image/gif;base64,{0}", base64);
var imageDecode = imgSrc;
if (base64 == "AA==")
{
imageDecode = "";
}
var result = new { motifDescription, imageDecode };
return Json(result, JsonRequestBehavior.AllowGet);
}
}
}
Another thing to remember and something that bites every newcomer is that you should not pass entities (objects from the context) to the views in models. This is because once the context is disposed, objects with navigational properties will break. There are ways around it but not recommended. Map the objects to models instead.
By the way, don't forget to call the SaveChanges() method after modifying entities or the database will not be updated with the changes.

You should really read very carefuly from some very good sources about DbContext: for example:
http://www.entityframeworktutorial.net/EntityFramework4.3/dbcontext-vs-objectcontext.aspx
https://msdn.microsoft.com/en-us/library/system.data.entity.dbcontext(v=vs.113).aspx

When you pass a DbContext to service or business class, you pass it as a Value not as a reference so you will loss all changes made in client code, the option is to pass it as a reference but it is not a safe and not a good practice but, if you instead pass the context as a delegate you are passing a reference to the object directly so its the best approch in order to keep your injected context with changes from business/service layers.
Here is the idea:
Option 1, pass it as reference, not recommended:
public void Call()
{
//Attach changes to context, Passing as reference
Process(ref _context);
//All changes attached to context
_context.SaveChanges();
}
public void Process(ref Cliniciel_WebRV_MasterEntities context)
{
var c = context();
//Get entites dbcontext
//Update entites
}
Option 2, pass it as a delegate, best approch:
public void Call()
{
//Attach changes to context, Passing as reference
Process(() => _context);
//All changes attached to context
_context.SaveChanges();
}
public void Process(Func<Cliniciel_WebRV_MasterEntities> context)
{
var c = context();
//Get entites dbcontext
//Update entites
}

Replace entity in context with a different instance of the same entity

I have an entity which is not connected to my dbcontext. I want to change that. However there is already another instance of the same entity attached to dbcontext. If I just add my new entity, I get an error, that an entity with the same primary key is already attached.
I tried multiple different variants of removing the old entity from dbcontext without any success. How can I replace the old instance with the new one?
Note: I don't want to copy the values, I want to attach this very instance of my new entity to dbcontext.
var entity = new MyEntity { Id = 1 };
var logicalDuplicate = dbcontext.Set<MyEntity >().Local
.FirstOrDefault(e => e.Equals(entity));
if (logicalDuplicate != null)
{
// remove logicalDuplicate from dbcontext
}
dbcontext.MyEntity.Attach(entity);
For clarification: I have overridden Equals to check for Id instead of reference.

Try this:
if (logicalDuplicate != null)
{
dbcontext.Entry(logicalDuplicate).State = EntityState.Detached;
dbcontext.MyEntity.Attach(entity);
dbcontext.Entry(entity).State = EntityState.Modified;
}
else
{
dbcontext.MyEntity.Add(entity);
}
How to get related entries
I investigated that and want to share with my results.
I used reflection as short way to get entity properties names. But it's possible to get it without reflection as mentioned #Florian Haider. You can use
answer and this.
// Found loaded related entries that can be detached later.
private HashSet<DbEntityEntry> relatedEntries;
private DbContext context;
private List<string> GetPropertiesNames(object classObject)
{
// TODO Use cache for that.
// From question https://stackoverflow.com/questions/5851274/how-to-get-all-names-of-properties-in-an-entity
var properties = classObject.GetType().GetProperties(BindingFlags.DeclaredOnly |
BindingFlags.Public |
BindingFlags.Instance);
return properties.Select(t => t.Name).ToList();
}
private void GetRelatedEntriesStart(DbEntityEntry startEntry)
{
relatedEntries = new HashSet<DbEntityEntry>();
// To not process start entry twice.
relatedEntries.Add(startEntry);
GetRelatedEntries(startEntry);
}
private void GetRelatedEntries(DbEntityEntry entry)
{
IEnumerable<string> propertyNames = GetPropertiesNames(entry.Entity);
foreach (string propertyName in propertyNames)
{
DbMemberEntry dbMemberEntry = entry.Member(propertyName);
DbReferenceEntry dbReferenceEntry = dbMemberEntry as DbReferenceEntry;
if (dbReferenceEntry != null)
{
if (!dbReferenceEntry.IsLoaded)
{
continue;
}
DbEntityEntry refEntry = context.Entry(dbReferenceEntry.CurrentValue);
CheckReferenceEntry(refEntry);
}
else
{
DbCollectionEntry dbCollectionEntry = dbMemberEntry as DbCollectionEntry;
if (dbCollectionEntry != null && dbCollectionEntry.IsLoaded)
{
foreach (object entity in (ICollection)dbCollectionEntry.CurrentValue)
{
DbEntityEntry refEntry = context.Entry(entity);
CheckReferenceEntry(refEntry);
}
}
}
}
}
private void CheckReferenceEntry(DbEntityEntry refEntry)
{
// Add refEntry.State check here for your need.
if (!relatedEntries.Contains(refEntry))
{
relatedEntries.Add(refEntry);
GetRelatedEntries(refEntry);
}
}

Edit This finds the original product, removes it, and adds the new one:
static void UpdateDatabase()
{
Context context = new Context();
Product product1 = context.Products.Find(1);
context.Products.Remove(product1);
Product product2 = new Product(){ProductId = 1, Name = "Product2"};
context.Products.Add(product2);
context.SaveChanges();
}

Best way to salve this problem is
db is my database Object
updateprice is my database entity object
ep is my old same database entity object
db.Entry(updateprice).CurrentValues.SetValues(ep);

Entity Framework - Many to Many relationship not saving to database

I have stumbled upon a problem with Entity Framework this morning.
I have following code mapping a modified entity and saving it into database.
public Group Save(Group x)
{
using (var db = new HostContext())
{
db.Projects.Attach(x.Project);
if (x.ID != 0)
{
db.AttachableObjects.Attach(x);
var manager = ((IObjectContextAdapter)db).ObjectContext.ObjectStateManager;
manager.ChangeObjectState(x, EntityState.Modified);
}
else
{
db.AttachableObjects.Add(x);
}
db.SaveChanges();
return x;
}
}
I call Save method with existing group as a parameter. Group contains one user I want to add as a member.
The method finishes successfully, however the relationship is not persisted in database.
Any help is very appreciated.
EDIT: These are my classes
class User : AttachableObject
{
...
private List<Group> memberof;
[DataMember]
[InverseProperty("Members")]
public List<Group> MemberOf
{
get { return memberof; }
set { memberof = value; }
}
...
}
class Group : AttachableObject
{
...
private List<User> members;
[DataMember]
[InverseProperty("MemberOf")]
public List<User> Members
{
get { return members; }
set { members = value; }
}
...
}
EDIT2: This is where the Save method is called
public Group AcceptInvite(int id)
{
var mapper = new InviteMapper();
var userMapper = new UserMapper();
var groupMapper = new GroupMapper();
var invite = mapper.Find(id);
if (invite != null)
{
var group = groupMapper.Find(invite.GroupID);
var user = userMapper.Find(invite.InviteeID);
group.Members.Add(user);
mapper.Delete(invite.ID);
return groupMapper.Save(group);
}
return null;
}
EDIT3: My mappers
public class GroupMapper
{
public Group Find(int id)
{
using (var db = new HostContext())
{
return db.AttachableObjects
.Include("Project")
.OfType<Group>().FirstOrDefault(x => x.ID == id);
}
}
}
The rest of the mappers is the same, only using their own tables.

You are not changing the relationship info of Project, you are only setting x to modified, relationship info must be changed explicitly.
So x.Project must have some property that points back to Group, you need to set it so the change is recorded.
I am guessing that x is resurrected via some deserialization process?

Save detached object graph using Entity Framework code first causes Primary Key violation

I'm trying to save an object graph of POCOs I have mapped to EF6 using Code First fluent notations.
Upon saving the object graph however, I stumble upon primary key violation exceptions.
The object graph is quite simple:
One Issue can contain multiple WorkItems with each one Author (as User).
The objects are populated externally (using a Web API)
When I attempt to save an issue with two workitems which refer to the same author, I would expect the issue to be inserted, the workitems to be inserted and one author to be inserted, and the other one to be referenced or be updated.
What happens however is that the issue is inserted, the workitems are inserted and both references to the same user are inserted, resulting in a primary key violation.
Simplified Issue object:
public class Issue
{
public Issue()
{
WorkItems = new List<WorkItem>();
}
public string Id { get; set; }
private List<WorkItem> _workItems;
public List<WorkItem> WorkItems
{
get { return _workItems ?? new List<WorkItem>(); }
set { _workItems = value; }
}
}
Simplified WorkItem:
public class WorkItem
{
public string Id { get; set; }
public string AuthorLogin
{
get; set;
}
private WorkItemAuthor _author;
public WorkItemAuthor Author
{
get { return _author; }
set { _author = value;
if (value != null)
{
AuthorLogin = value.Login;
}
else
{
AuthorLogin = string.Empty;
}
}
}
}
Simplified user object:
public class User
{
public string Login { get; set; }
public string FullName { get; set; }
}
Their Code-first configurations:
internal IssueConfiguration()
{
HasKey(x => x.Id);
HasMany(x => x.WorkItems);
}
internal WorkItemConfiguration()
{
HasKey(x => x.Id);
HasRequired(p => p.Author)
.WithMany(b => b.WorkItems)
.HasForeignKey(x=>x.AuthorLogin);
}
internal UsersConfiguration()
{
HasKey(x => x.Login);
}
All quite straightforward. Upon database create, de tables look fine and dandy too, with FKs on the columns where one would expect them
Now when saving the issue, it would have been nice if the object graph would be inserted, and the reference to existing objects would be recognized automagically and optionally inserted or referenced only.
I attempt to add issues accordingly:
using (var db = new Cache.Context())
{
if (db.Issues.Any(e => e.Id == issue.Id))
{
db.Issues.Attach(issue);
db.Entry(issue).State = EntityState.Modified;
}
else
{
db.Issues.Add(issue);
}
db.SaveChanges();
}
Is the solution to this issue that I walk through the object graph to manually add or attach the other objects in the graph too? I would expect by defining the proper Foreign Key values these references would be recognized.

I finally ended up doing something similar to this, quite laborious and I would still like to find a better way.
Finding out whether an entity is already attached or exists in the database turned out to be pollute the model too much (implementing IEquatable<T> is fine, but I think implementing IEntityWithKey on my POCOs pollutes the POCO too much. (and till that did not seem to suffice tracking entities in the context)
internal static void Save(this List<Issue> issues)
{
using (var db = new Context())
{
foreach (var issue in issues.ToList())
{
foreach (var workItem in issue.WorkItems.ToList())
{
if (workItem.Author != null)
{
var existing = db.Users.SingleOrDefault(e => e.Login == workItem.Author.Login);
if (existing == null)
{
db.Users.Add(workItem.Author);
}
else
{
//Update existing entities' properties
existing.Url = workItem.Author.Url;
//Replace reference
workItem.Author = existing;
}
db.SaveChanges();
}
var existingWorkItem = db.WorkItems.SingleOrDefault(e => e.Id == workItem.Id);
if (existingWorkItem == null)
{
db.WorkItems.Add(workItem);
}
else
{
//Update existing entities' properties
existingWorkItem.Duration = workItem.Duration;
//Replace reference
issue.WorkItems.Remove(workItem);
issue.WorkItems.Add(existingWorkItem);
}
db.SaveChanges();
}
var existingIssue = db.Issues.SingleOrDefault(x => x.Id == issue.Id);
if (existingIssue == null)
{
db.Issues.Add(issue);
}
else
{
//Update existing entities' properties
existingIssue.SpentTime = issue.SpentTime;
}
db.SaveChanges();
}
}
}

There is a small bug in the Issue object.
"return _workItems ?? new List();" could return a new WorkItem on every get if _workItems ever became null. Here is the fixed version.
public class Issue {
public Issue() {
WorkItems = new List<WorkItem>();
}
public String Id {
get; set;
}
public List<WorkItem> WorkItems { get; private set; }
}