We have an ASP.Net MVC application that uses EF4 as its data access layer and we're seeing unexpected behaviour with regards to OptimisitcConcurrencyExceptions not being thrown when we think they should be.
We have simplified the problem down to the following code...
using System.Linq;
using Project.Model;
namespace OptimisticConcurrency
{
class Program
{
static void Main()
{
Contact firstContact = null;
using (var firstEntities = new ProjectEntities())
{
firstContact = (from c in firstEntities.Contacts
where c.LastName == "smith" select c).Single();
}
using (var secondEntities = new ProjectEntities())
{
var secondContact = (from c in secondEntities.Contacts
where c.LastName == "smith" select c).Single();
secondContact.Title = "a";
secondEntities.SaveChanges();
}
firstContact.Title = "b";
using (var thirdEntities = new ProjectEntities())
{
var thirdContact = (from c in thirdEntities.Contacts
where c.LastName == "smith" select c).Single();
thirdContact.Title = firstContact.Title;
//EXPLICITLY SET VERSION HERE
thirdContact.Version = firstContact.Version;
thirdEntities.SaveChanges();
}
}
}
}
This is a rather simple version of what happens in our MVC app, but the same problem occurs.
When we call SaveChanges on the thirdEntities, I expect the exception and nothing is being thrown.
Much more interestingly, when we attach the SQL Profiler, we see that the Version is being used in the where clause but it is thirdEntities Version value (the current one in the DB) being used, not the firstEntities values DESPITE it being explicitly set immediately before SaveChanges is called. SaveChanges is resetting the Version to be the retrieved value not the set value.
In the EDMX, the Version is set to have a StoreGeneratedPattern is set to Computed.
Anyone have any idea what is going on here?
This is a problem. Once the column is set to Computed you can't set its value in the application (you can but the value is not used).
Edit:
If you load entity from database it is by default tracked with the context. The context stores its original values. Original values are for example used for snapshot change tracking but they are also used as the only valid source of Computed properties. If you set Computed property in your entity the value is not used and original value is used insted. The workaround is to modify original value (before you modify anything else):
using (var context = new TestEntities())
{
var entityToUpdate = context.MyEntities.Single(e => e.Id == someId);
entityToUpdate.Timestamp = entity.Timestamp;
ObjectStateEntry entry = context.ObjectStateManager.GetObjectStateEntry(entityToUpdate);
entry.ApplyOriginalValues(entityToUpdate);
// set modified properties
context.SaveChanges();
}
Edit 2:
Btw. once you have both actually loaded timestamp and previously retrieved timestamp you can simply compare them in your application instead of doing it in the database.
Related
I need to add a record to a database using the Entity Framework. Since I'm brand new to using this syntax I am not sure how to properly write the code (Below is my best guess).
First, the agent must have their info inserted into the Agent table. This table produces a self-incrementing primary key known as a SymNumber. I then need to take that SymNumber and use it as a primary key for an insert into the AgentIdentification table.
I have run this code a couple of times, and I do not come up with an error, however since I am using a unit test to test the code I cannot tell for sure if the agent is being added properly. Secondly, I know for a fact that I am not correctly grabbing the SymNumber as generated by the Agent table after the first insert. The SymNumber is an int value in the Linq code set to 0, and this does not change during the AgentIdentification insert.
Any help would be greatly appreciated!
AgentResourcesEntities _db = new AgentResourcesEntities();
try
{
Agent agent = new Agent();
agent.EntityType = "P";
agent.FirstName = agentNewTraining.FirstName;
agent.LastName = agentNewTraining.LastName;
agent.LastChangeOperator = agentNewTraining.Requestor;
agent.LastChangeDate = DateTime.Now;
if (!String.IsNullOrEmpty(agentNewTraining.NameSuffix)) agent.NameSuffix = agentNewTraining.NameSuffix;
_db.Agent.AddObject(agent);
AgentIdentification agentIdentification = new AgentIdentification();
agentIdentification.SymNumber = agent.SymNumber;
agentIdentification.ReferenceType = "S";
agentIdentification.DummyReference = 0;
agentIdentification.LastChangeOperator = agentNewTraining.Requestor;
agentIdentification.LastChangeDate = DateTime.Now;
_db.AgentIdentification.AddObject(agentIdentification);
return true;
}
catch (Exception)
{
return false;
}
First you need to call
_db.SaveChanges();
to get your changed persisted.
But if you want also synchronize (get the new generated value) your agent.SymNumber you will need to call SaveChanges() right after adding it to context.
So the code will be like:
/// ...... ////
_db.Agent.AddObject(agent);
_db.SaveChanges();
AgentIdentification agentIdentification = new AgentIdentification();
agentIdentification.SymNumber = agent.SymNumber; // sym number is now synchronized from DB
///...../////
_db.AgentIdentification.AddObject(agentIdentification);
_db.SaveChanges();
But if SymNumber is foreign key so the AgentIdentification has could have reference to some Agent instance, you can just tie those instances with that reference and would not need to call that additional SaveChanges() in the middle.
Call _db.SaveChanges() after inserting.
I have code that generates records based on my DataGridView. These records are temporary because some of them already exist in the database.
Crop_Variety v = new Crop_Variety();
v.Type_ID = currentCropType.Type_ID;
v.Variety_ID = r.Cells[0].Value.ToString();
v.Description = r.Cells[1].Value.ToString();
v.Crop = currentCrop;
v.Crop_ID = currentCrop.Crop_ID;
Unfortunately in this little bit of code, because I say that v.Crop = currentCrop,
now currentCrop.Crop_Varieties includes this temporary record. And when I go to insert the records of this grid that are new, they have a reference to the same Crop record, and therefore these temporary records that do already exist in the database show up twice causing duplicate key errors when I submit.
I have a whole system for detecting what records need to be added and what need to be deleted based on what the user has done, but its getting gummed up by this relentless tracking of references.
Is there a way I can stop Linq-To-Sql from automatically adding these temporary records to its table collections?
I would suggest revisiting the code that populates DataGridView (grid) with records.
And then revisit the code that operates on items from a GridView, keeping in mind that you can grab bound item from a grid row using the following code:
public object GridSelectedItem
{
get
{
try
{
if (_grid == null || _grid.SelectedCells.Count < 1) return null;
DataGridViewCell cell = _grid.SelectedCells[0];
DataGridViewRow row = _grid.Rows[cell.RowIndex];
if (row.DataBoundItem == null) return null;
return row.DataBoundItem;
}
catch { }
return null;
}
}
It is also hard to understand the nature of Crop_Variety code that you have posted. As the Crop_Variety seems to be a subclass of Crop. This leads to problems when the Crop is not yet bound to database and potentially lead to problems when you're adding Crop_Variety to the context.
For this type of Form application I normally have List _dataList inside form class, then the main grid is bound to that list, through ObjectBindingList or another way. That way _dataList holds all data that needs to be persisted when needed (user clicked save).
When you assign an entity object reference you are creating a link between the two objects. Here you are doing that:
v.Crop = currentCrop;
There is only one way to avoid this: Modify the generated code or generate/write your own. I would never do this.
I think you will be better off by writing a custom DTO class instead of reusing the generated entities. I have done both approaches and I like the latter one far better.
Edit: Here is some sample generated code:
[global::System.Data.Linq.Mapping.AssociationAttribute(Name="RssFeed_RssFeedItem", Storage="_RssFeed", ThisKey="RssFeedID", OtherKey="ID", IsForeignKey=true, DeleteOnNull=true, DeleteRule="CASCADE")]
public RssFeed RssFeed
{
get
{
return this._RssFeed.Entity;
}
set
{
RssFeed previousValue = this._RssFeed.Entity;
if (((previousValue != value)
|| (this._RssFeed.HasLoadedOrAssignedValue == false)))
{
this.SendPropertyChanging();
if ((previousValue != null))
{
this._RssFeed.Entity = null;
previousValue.RssFeedItems.Remove(this);
}
this._RssFeed.Entity = value;
if ((value != null))
{
value.RssFeedItems.Add(this);
this._RssFeedID = value.ID;
}
else
{
this._RssFeedID = default(int);
}
this.SendPropertyChanged("RssFeed");
}
}
}
As you can see the generated code is establishing the link by saying "value.RssFeedItems.Add(this);".
In case you have many entities for wich you would need many DTOs you could code-generate the DTO classes by using reflection.
I´m still having a hard time with Linq.
I need to write a Update Function tat receives an object that has a list. Actually, A region has a list of cities. I want to pass an object "Region" that has a name filed and a list of cities. The problem, is the city objects came from another context and I am unable to attach them to this context. I have been trying several functions, and always get an error like "EntitySet was modified during enumeration" or other. I am tring to make the code below work, but if anyone has a different approach please help.
public int Updateregion(region E)
{
try
{
using (var ctx = new AppDataDataContext())
{
var R =
(from edt in ctx.regiaos
where edt.ID == E.ID
select edt).SingleOrDefault();
if (R != null)
{
R.name = R.name;
R.description = E.description;
}
R.cities = null;
R.cities.AddRange(Edited.Cities);
ctx.SubmitChanges();
return 0 //OK!
}
}
catch (Exception e)
{
......
}
You can't attach objects retrieved from one datacontext to another, it's not supported by Linq-to-SQL. You need to somehow dettach the objects from their original context, but this isn't supported either. One can wonder why a dettach method isn't available, but at least you can fake it by mapping the list to new objects:
var cities = Edited.Cities.Select(city => new City {
ID = city.ID,
Name = city.Name,
/* etc */
});
The key here is to remember to map the primary key and NOT map any of the relation properties. They must be set to null. After this, you should be able to attach the new cities list, and have it work as expected.
Is it possible to apply a WHERE clause on a SubSonic query?
For example, I get get a single based on id...
db.Single<Storage>(id);
But how can I get a single based on a simple WHERE clause?
db.Single<Storage>(WHERE columnname == "value");
that's possible:
// Will return a Storage instance with property IsNew = true, if record does not exist
// since an object created with new never can be null
var storage1 = new Storage(1); // id = 1
var storage1 = new Storage(Storag.Columns.ColumnName, "value");
// Will return 0 if record not found (subsonic3 only)
var storage3 = (from s in Storage
where s.ColumnName == "value"
select s).SingleOrDefault();
// Will throw an exception if record not found (subsonic3 only)
var storage3 = (from s in Storage
where s.ColumnName == "value"
select s).Single();
Since db is a partial class you can extend it. Just create a new File within the same namespace (but another folder in your solution). This applies to subsonic 2 but will be similar to subsonic 3, I think.
public static partial class DB
{
public static T Single<T>(String columName, Object columnValue) where T: RecordBase<T>, new()
{
return Select().From<T>()
.Where(columnName).IsEqualTo(columnValue)
.ExecuteSingle<T>();
}
}
Thanks for the above, this was a help and eventually I simplified this to the below...
db.Single<Storage>(s => s.ColumnName == "value");
After going through Entity Framework I have a couple of questions on implementing auditing in Entity Framework.
I want to store each column values that is created or updated to a different audit table.
Right now I am calling SaveChanges(false) to save the records in the DB(still the changes in context is not reset). Then get the added | modified records and loop through the GetObjectStateEntries. But don't know how to get the values of the columns where their values are filled by stored proc. ie, createdate, modifieddate etc.
Below is the sample code I am working on it.
// Get the changed entires( ie, records)
IEnumerable<ObjectStateEntry> changes = context.ObjectStateManager.GetObjectStateEntries(EntityState.Modified);
// Iterate each ObjectStateEntry( for each record in the update/modified collection)
foreach (ObjectStateEntry entry in changes)
{
// Iterate the columns in each record and get thier old and new value respectively
foreach (var columnName in entry.GetModifiedProperties())
{
string oldValue = entry.OriginalValues[columnName].ToString();
string newValue = entry.CurrentValues[columnName].ToString();
// Do Some Auditing by sending entityname, columnname, oldvalue, newvalue
}
}
changes = context.ObjectStateManager.GetObjectStateEntries(EntityState.Added);
foreach (ObjectStateEntry entry in changes)
{
if (entry.IsRelationship) continue;
var columnNames = (from p in entry.EntitySet.ElementType.Members
select p.Name).ToList();
foreach (var columnName in columnNames)
{
string newValue = entry.CurrentValues[columnName].ToString();
// Do Some Auditing by sending entityname, columnname, value
}
}
Here you have two basic options:
Do it at the database level
Do it in the c# code
Doing it at the data base level, means using triggers. In that case there is no difference if you are using enterprise library or another data access technology.
To do it in the C# code you would add a log table to your datamodel, and write the changes to the log table. When you do a save changes both the changes to the data and the information which you wrote to the log table would be saved.
Are you inserting the new record using a stored proc? If not (i.e. you are newing up an object, setting values, inserting on submit and then saving changes the new object id will be automatically loaded into the id property of the object you created. If you are using a stored proc to do the insert then you need to return the ##IDENTITY from the proc as a return value.
EX:
StoreDateContext db = new StoreDataContext(connString);
Product p = new Product();
p.Name = "Hello Kitty Back Scratcher";
p.CategoryId = 5;
db.Products.Add(p);
try
{
db.SaveChanges();
//p.Id is now set
return p.Id;
}
finally
{
db.Dispose;
}